Reversal of evoked gamma oscillation deficits is predictive of antipsychotic activity with a unique profile for clozapine. (2016)

Reversal of evoked gamma oscillation deficits is predictive of antipsychotic activity with a unique profile for clozapine.

Recent heuristic models of schizophrenia propose that abnormalities in the gamma frequency cerebral oscillations may be closely tied to the pathophysiology of the disorder, with hypofunction of N-methyl-d-aspartate receptors (NMDAr) implicated as having a crucial role. Prepulse inhibition (PPI) is a behavioural measure of sensorimotor gating that is disrupted in schizophrenia. We tested the ability for antipsychotic drugs with diverse pharmacological actions to (1) ameliorate NMDAr antagonist-induced disruptions to gamma oscillations and (2) attenuate NMDAr antagonist-induced disruptions to PPI. We hypothesized that antipsychotic-mediated improvement of PPI deficits would be accompanied by a normalization of gamma oscillatory activity. Wistar rats were implanted with extradural electrodes to facilitate recording of electroencephalogram during PPI behavioural testing. In each session, the rats were administered haloperidol (0.25 mg kg(-1)), clozapine (5 mg kg(-1)), olanzapine (5 mg kg(-1)), LY379268 (3 mg kg(-1)), NFPS (sarcosine, 1 mg kg(-1)), d-serine (1800 mg kg(-1)) or vehicle, followed by the NMDAr antagonists MK-801(0.16 mg kg(-1)), ketamine (5 mg kg(-1)) or vehicle. Outcome measures were auditory-evoked, as well as ongoing, gamma oscillations and PPI. Although treatment with all the clinically validated antipsychotic drugs reduced ongoing gamma oscillations, clozapine was the only compound that prevented the sensory-evoked gamma deficit produced by ketamine and MK-801. In addition, clozapine was also the only antipsychotic that attenuated the disruption to PPI produced by the NMDAr antagonists. We conclude that disruptions to evoked, but not ongoing, gamma oscillations caused by NMDAr antagonists are functionally relevant, and suggest that compounds, which restore sensory-evoked gamma oscillations may improve sensory processing in patients with schizophrenia.

That said, I really want to avoid using clozapine again! Would have been interesting to see if other SGAs augmented with NMDAR glycine site agonists etc  performed any better.


Clozapine discontinuation – some experiences and a new animal model of schizophrenia

It’s four days today since I stopped clozapine (50mg at night). Some rebound insomnia was expected but it’s proving to be more problematic than I’d hoped. That, coupled with the activating effects of aripiprazole (30mg) has left me quite sleep deprived but thankfully not psychotic. It’s a fine line though… one I don’t want to cross yet another time. I attempted to sleep on doxylamine (25mg) but even that was ineffective, giving me a fragmented drowsiness but no proper sleep.

A case of rebound insomnia (on ceasing 75mg) has been reported [1]:

“Rebound insomnia has been reported upon discontinuation of benzodiazepines. We describe the first case of a sleep polygraphically documented rebound insomnia with an unusual somatic fatigue syndrome after long-term use of clozapine in a 30-year-old schizophrenic male. The withdrawal symptoms occurred the first day after drug discontinuation and could be stopped by readministering clozapine. In our opinion, the sudden occurrence of the withdrawal symptoms cannot be explained by a dopaminergic hypersensitivity or a cholinergic rebound, but indicates an involvement of GABAergic and perhaps antiglutamatergic properties of clozapine.”

The whole aim was to avoid getting back on any sedating/weight gaining antipsychotics (which is the next step if I can’t sleep) so I’ll persist with doxylamine for a few nights and maybe see if melatonin can help ‘reset’ things.

Update: Doxylamine (50mg) on the fourth night was slightly more effective but I still only had a broken sleep. Doxylamine (50mg) and melatonin (10mg) on the fifth night resulted in a more solid sleep.

More severe withdrawal symptoms have also been reported  “withdrawal symptoms for clozapine can be severe with rapid onset of agitation, abnormal movements, and psychotic symptoms” [2] The authors in this article concluded: “The severe agitation and psychotic symptoms after clozapine withdrawal in these three patients were due to delirium, perhaps the result of central cholinergic rebound. The withdrawal symptoms and delirium resolved rapidly with resumption of low doses of clozapine. Severe withdrawal symptoms can probably be avoided by slowly tapering clozapine and/or simultaneously substituting another psychotropic with high anticholinergic activity”.


Diurnal neurobiological alterations after exposure to clozapine in first-episode schizophrenia patients.

Irregular circadian rhythm and some of its most characteristic symptoms are frequently observed in patients with schizophrenia. However, changes in the expression of clock genes or neuropeptides that are related to the regulation of circadian rhythm may influence the susceptibility to recurrence after antipsychotic treatment in schizophrenia, but this possibility has not been investigated. Blood samples were collected from 15 healthy male controls and 13 male schizophrenia patients at 4h intervals for 24h before and after treatment with clozapine for 8 weeks. The outcome measures included the relative expression of clock gene mRNA PERIOD1 (PER1), PERIOD2 (PER2), PERIOD3 (PER3) and the levels of plasma cortisol, orexin, and insulin. Compared with healthy controls, schizophrenia patients presented disruptions in diurnal rhythms of the expression of PER1, PER3, and NPAS2 and the release of orexin, accompanied by a delayed phase in the expression of PER2, decreases in PER3 and NPAS2 expression, and an increase in cortisol levels at baseline. Several of these disruptions (i.e., in PER1 and PER3 expression) persisted after 8 weeks of clozapine treatment, similar to the decreases in the 24-h expression of PER3 and NPAS2. Clozapine treatment for 8 weeks significantly decreased the 24-h levels of PER2 and increased the 24-h levels of insulin. These persistent neurobiological changes that occur after 8 weeks of clozapine treatment may contribute to the vulnerability to recurrence and efficacy of long-term maintenance treatment in schizophrenia.

It’s interesting to see an animal model of schizophrenia using abrupt clozapine withdrawal, this one implicating changes in GABA release on discontinuation of clozapine [3 [full text]]:

“Schizophrenia disease models are necessary to elucidate underlying changes and to establish new therapeutic strategies towards a stage where drug efficacy in schizophrenia (against all classes of symptoms) can be predicted. Here we summarise the evidence for a GABA dysfunction in schizophrenia and review the functional neuroanatomy of five pathways implicated in schizophrenia, namely the mesocortical, mesolimbic, ventral striopallidal, dorsal striopallidal and perforant pathways including the role of local GABA transmission and we describe the effect of clozapine on local neurotransmitter release. This review also evaluates psychotropic drug-induced, neurodevelopmental and environmental disease models including their compatibility with brain microdialysis. The validity of disease models including face, construct, etiological and predictive validity and how these models constitute theories about this illness is also addressed. A disease model based on the effect of the abrupt withdrawal of clozapine on GABA release is also described. The review concludes that while no single animal model is entirely successful in reproducing schizophreniform symptomatology, a disease model based on an ability to prevent and/or reverse the abrupt clozapine discontinuation-induced changes in GABA release in brain regions implicated in schizophrenia may be useful for hypothesis testing and for in vivo screening of novel ligands not limited to a single pharmacological class.”

Hopefully my experiences will be transient and resolve on their own but management of clozapine discontinuation is an area that needs careful consideration.  If anyone has any experiences with clozapine discontinuation and how they managed any rebound phenomena, please feel free to share.

Adjunctive Minocycline in Clozapine-Treated Schizophrenia Patients With Persistent Symptoms (2015)

Adjunctive Minocycline in Clozapine-Treated Schizophrenia Patients With Persistent Symptoms (2015)

Clozapine is the most effective antipsychotic for treatment refractory people with schizophrenia, yet many patients only partially respond. Accumulating preclinical and clinical data suggest benefits with minocycline. We tested adjunct minocycline to clozapine in a 10-week, double-blind, placebo-controlled trial. Primary outcomes tested were positive, and cognitive symptoms, while avolition, anxiety/depression, and negative symptoms were secondary outcomes. Schizophrenia and schizoaffective participants (n = 52) with persistent positive symptoms were randomized to receive adjunct minocycline (100 mg oral capsule twice daily; n = 29) or placebo (n = 23). Brief Psychiatric Rating Scale (BPRS) psychosis factor (P = 0.098; effect size [ES], 0.39) and BPRS total score (P = 0.075; ES, 0.55) were not significant. A change in total BPRS symptoms of more than or equal to 30% was observed in 7 (25%) of 28 among minocycline and 1 (4%) of 23 among placebo participants, respectively (P = 0.044). Global cognitive function (MATRICS Consensus Cognitive Battery) did not differ, although there was a significant variation in size of treatment effects among cognitive domains (P = 0.03), with significant improvement in working memory favoring minocycline (P = 0.023; ES, 0.41). The Scale for the Assessment of Negative Symptoms total score did not differ, but significant improvement in avolition with minocycline was noted (P = 0.012; ES, 0.34). Significant improvement in the BPRS anxiety/depression factor was observed with minocycline (P = 0.028; ES, 0.49). Minocycline was well tolerated with significantly fewer headaches and constipation compared with placebo. Minocycline’s effect on the MATRICS Consensus Cognitive Battery composite score and positive symptoms were not statistically significant. Significant improvements with minocycline were seen in working memory, avolition, and anxiety/depressive symptoms in a chronic population with persistent symptoms. Larger studies are needed to validate these findings.

“There are no evidence-based treatments available for people who are partially or completely nonresponsive to CLZ and continue to have persistent symptoms. Lamotrigine is 1 medication that has some positive data adjunctive to CLZ on psychotic symptoms. However, its efficacy has been demonstrated in only 1 study and recently not been replicated; thus it remains questionable if it is an effective strategy. It is notable that lamotrigine added to other antipsychotics have not been effective, thus, if it has efficacy as an adjunct may possibly work synergistically through glutamatergic pathways. It is believed that lamotrigine functions as an ionotropic α-amino-3-hydroxy-5-methyl-4-isoxazol-propionate (AMPA) glutamate receptor modulator.”


  • crosses the blood-brain barrier and has recently been found to have an effect on the GluR1 AMPA receptor subtype
  • is known to have anti-inflammatory actions and inhibits inflammatory enzymes
  • directly inhibits the proliferation of, as well as attenuates, microglia activation

“Preliminary human studies in schizophrenia suggest potential benefits from minocycline. Initial case reports of minocycline-associated improvements in persistent psychotic symptoms led to an open-label 4-week study, which linked minocycline to mean reductions of over 50% in the Positive and Negative Syndrome Scale general psychopathology scale scores.A handful of recent clinical trial publications and a meta-analysis have report benefits (mostly negative symptoms) of minocycline, mostly in early episode and with medications other than CLZ.

Three small case reports, including one from our own group, have specifically reported symptom benefits from minocycline added to CLZ.The current study is the first double-blind, randomized controlled trial of adjunctive minocycline to CLZ in schizophrenia with persistent symptoms. We hypothesized that we would observe a significant improvement in positive and cognitive symptoms as well as that minocycline might have effects on negative symptoms (particularly avolition) and anxiety/depressive symptoms.”

“To date, there have been 4 published randomized, double-blind trials with minocycline, all finding some positive effects in cognitive function, negative symptoms, or positive symptoms but with differing inclusion and exclusion criteria and primary outcomes. In the first study published, Levkovitz et al studied minocycline as an adjunct treatment to treatment as usual for negative and cognitive symptoms in patients within the first 5 years of illness. The study of Chaudhry et al was a 2-site study with adjunct treatment of minocycline to treatment as usual in patients in the first 5 years of their illness but with both positive and negative symptoms as the primary outcomes. Liu et al studied adjunct minocycline to risperidone in patients in the first 5 years of illness but with negative symptoms as the primary outcome. Lastly, Khodaie-Ardakani et al also added minocycline to risperidone and with negative symptoms as the primary outcome but in a chronic population. This study that we present is different in that it is the first study with minocycline treatment as adjunct to CLZ, the first to have positive and cognitive symptoms as the primary outcomes and only the second to test in a chronic population. Our study failed to find significant results in positive and global cognitive symptoms and may not have been powered to find a difference in global negative symptoms. In secondary analyses, we did find significant improvements in the areas of avolition, working memory, and anxiety/depression.

Our prior case series of CLZ patients treated openly with adjunct minocycline reported improved positive symptoms but also improvements in motivation for social and school interactions and activities. Avolition is a core symptom of schizophrenia, which leads to a decrease in spontaneous, self-initiated, and purposeful behaviors observed in daily life activities. A unique domain within the negative symptom syndrome, avolition is often associated with poorer functional outcome. The domain of amotivation or avolition has been found to be a strong predictor of interpersonal relations and personal and social function. Avolition is thought to be due to aberrant cortical-striatal interactions that facilitate reward processing. Negative symptoms more generally have been found to be associated with higher levels of inflammation. Similarly, evidence of inflammation is more common in deficit versus nondeficit schizophrenia. Glutamate dysfunction may also underlie negative symptoms. The anti-inflammatory effects of minocycline and/or its modulation of glutamatergic pathways could underlie the avolition benefits we have observed. Although we observed a positive finding for avolition, the study may not have been powered to detect improvements in global negative symptoms.

Working memory is also regarded as a core deficit in schizophrenia.The improvements in working memory seen here are consistent with Levkovitz et al who also found improvements in working memory in early-phase schizophrenia patients, some of whom were taking CLZ. Working deficits have been found to be connected to inflammation. Liaury et al found that microglial activation was attenuated with related improvements in memory related to inflammation during minocycline treatment. Microglial cells are known to contribute to synaptic modulation, learning, and memory processes. Many other animal studies have found minocycline to reduce memory and working memory deficits in animal models.The relevance of this literature to the current results should be viewed with tempered enthusiasm given that the clinical importance of the modest but statistically significant improvement in working memory we observed is questionable”


“Minocycline was well tolerated in this 10-week study. As noted, beneficial effects were noted in headache, constipation, and HDL levels. Changes in skin pigmentation were seen in a few participants; however, no one discontinued the study because of skin pigmentation. We also did not see gastrointestinal adverse effects or differences in weight gain, suggesting that minocycline could be tolerable as an adjunctive medication in a schizophrenia population. Other minocycline studies in schizophrenia also have had very good tolerability; however, in a few clinical trials, there have been gastrointestinal complaints such as nausea, diarrhea, and constipation that occurred more frequently with minocycline than in the placebo group, but most of these studies have used doses of up to 400 mg/d. In addition, it is important to point out that minocycline has been identified as a causative agent of drug-induced lupus (DIL), which has a similar presentation to systemic lupus erythematosus”


“Our study is limited by small sample size, lack of power for negative symptoms, and the fact that change in functional outcomes from negative symptoms and cognitive improvements generally take longer than 10 weeks, as seen in longer term studies and case reports with minocycline,which have reported functional improvements. Nonetheless, our moderate effects in some treatment domains in a chronically ill and treatment-resistant population are worth noting. Our sample of CLZ-treated participants had undergone at least 6 months and commonly years of CLZ treatment, with partial improvement, but continued moderate to severe symptoms. This is a difficult to treat population with little evidence for efficacious adjunctive treatments. The current data and other published data continue to suggest that minocycline is a possible adjunctive medication. Future analyses of these data will examine inflammatory markers and imaging data to better evaluate biomarkers for treatment response. These data add to the growing evidence suggesting that minocycline is a worthwhile adjunct treatment to consider when first-line agents are not enough.”

See also:

Effects of minocycline add-on treatment on brain morphometry and cerebral perfusion in recent-onset schizophrenia.

Augmenting in clozapine non/partial responders

Levothyroxine Augmentation in Clozapine Resistant Schizophrenia: A Case Report and Review (2015)

Levothyroxine Augmentation in Clozapine Resistant Schizophrenia: A Case Report and Review

There are many reports that show different thyroid abnormalities in schizophrenia without clear establishment of their role in etiology and treatment outcome of schizophrenia. Among these reports, there are only a few that consider a role for thyroid hormones as augmenting agents in the treatment with antipsychotic drugs. This case report outlines symptom subsidence of a patient with clozapine refractory paranoid schizophrenia and normal thyroid function who added levothyroxine to clozapine and found that symptoms of psychosis returned once levothyroxine was discontinued. Although this observation needs to be confirmed in controlled clinical trials, we aimed to discuss possible hypothesized mechanisms underlying this observation.

“The patient was hospitalized with a confirmed diagnosis of refractory paranoid schizophrenia, and clozapine was administered with a gradually increasing dose, up to 600 mg per day. After six weeks, she was significantly calmer with lower anxiety and aggression, her sleep quality had improved, and her appetite had increased. However, she was still experiencing social withdrawal, persecutory and reference delusions, and visual hallucinations. Despite good drug adherence, psychosis continued four months after discharge. Afterwards, without our knowledge, the mother, who had hypothyroidism, advised the patient to use levothyroxine (at a dose of 0.1 mg per day) in addition to clozapine. After two weeks with this treatment, hallucinations and delusions completely subsided, and the patient’s social relations improved. When we were informed, discontinuation of levothyroxine was advised, given her normal thyroid tests. About three weeks after the removal of levothyroxine, psychosis symptoms gradually reappeared (despite still taking clozapine). The patient was again experiencing hallucinations and delusions.”

“About 30–36% of patients with chronic schizophrenia have abnormal thyroid tests, but, in clinical terms, they are euthyroid. These abnormalities may disappear following successful treatment of schizophrenia and may also have a correlation with treatment response to antipsychotics. For instance, it has been observed that higher T3 serum levels in patients with chronic schizophrenia are related to their better cognitive functions and lower extrapyramidal drug side effects. It has also been seen that high basal TSH is associated with poorer response and blunted TSH response to thyrotropin releasing hormone (TRH) and a high level of T4 before treatment with better response to treatment. T4 levels before treatment are also positively correlated with severity of the disorder. Although the results of studies are contradictory, they mostly cite increased total and free T4 in patients with schizophrenia before treatment and their normalization after treatment”

Tailoring ratios of clozapine to N-desmethylclozapine (norclozapine)

A meta-analysis of the effects of SGAs on cognition has recently been published, with clozapine performing poorly in some domains [1]

Interestingly, other research has hinted at the possible benefits of tailoring clozapine to norclozapine (N-desmethylclozapine, NDMC) ratios:

Prediction of Working Memory Performance in Schizophrenia by Plasma Ratio of Clozapine to N-Desmethylclozapine.

Clozapine’s potent antagonism of muscarinic M1 receptors is thought to worsen working memory deficits associated with schizophrenia. In contrast, its major metabolite, N-desmethylclozapine (NDMC), is thought to enhance working memory via its M1 receptor agonist activity. The authors hypothesized that the ratio of serum clozapine and NDMC concentrations would be inversely associated with working memory performance in schizophrenia. Thirty patients with schizophrenia or schizoaffective disorder who were receiving clozapine monotherapy at bedtime completed the MATRICS Consensus Cognitive Battery (MCCB) on the day their blood was collected to assess concentrations of clozapine and NDMC as well as serum anticholinergic activity. The clozapine/NDMC ratio was significantly and negatively associated with working memory performance after controlling for age, gender, education, and symptom severity. No significant associations were found between individual clozapine and NDMC concentrations and working memory performance. Serum anticholinergic activity was significantly associated with clozapine concentration, but not with working memory performance or NDMC concentration. No significant associations were found between any pharmacological measure and performance on other MCCB cognitive domains. This hypothesis-driven study confirms that clozapine/NDMC ratio is a strong predictor of working memory performance in patients with schizophrenia. This finding suggests that manipulating the clozapine/NDMC ratio could enhance cognition in patients with schizophrenia treated with clozapine. It also supports the study of procholinergic agents, such as M1 receptor-positive allosteric modulators, to enhance cognition in schizophrenia.

A patent has been filed: “Use of N-desmethylclozapine to treat human neuropsychiatric disease

“Administration of clozapine to human subjects results in the formation of two major metabolites N-desmethylclozapine (NDMC) and clozapine-N-oxide. However, clozapine-N-oxide is a polar metabolite that is rapidly excreted and likely does not contribute to the biological activity of the parent compound. A correlation exists between the dose of clozapine administered to a subject, and the serum levels of total clozapine moieties, yet the levels of NDMC can vary widely between individual subjects. Generally, NDMC constitutes 40-75% of the total serum clozapine concentrations during steady state kinetics in humans… observations demonstrate that NDMC has been routinely administered to human subjects, and is well tolerated.

Surprisingly, and unlike the closely related compound clozapine, it has been found that the compound N-desmethylclozapine (NDMC) possesses heretofore unappreciated functional activity as a muscarinic receptor agonist. Ex vivo experiments have demonstrated that NDMC crosses the blood brain barrier and acts as an agonist at central muscarinic receptors in rats. These observations have practical applications that support the use of NDMC as an antipsychotic, antimania agent, antidementia agent, and as a therepeutic agent to treat glaucoma or neuropathic pain.”

Pharmacological profile of NDMC:

“NDMC is a metabolite of clozapine with a similar receptor profile as clozapine; it has partial agonist activity at the dopamine 2 (D2) receptor family, but is non-reactive at D3. N-desmethylclozapine (NDMC) is an allosteric partial agonist at the M1 receptor, where clozapine is a functional antagonist or partial agonist. NDMC has high agonist efficacy at M1 (partial), M4, and M5, but antagonist activity at M3; this would lead to fewer adverse side effects. NDMC-induced phosphorylation of mitogen-activated protein kinase, which was dose-dependent, was blocked by scopolamine; this action is consistent with M1 activation. NDMC also crosses the blood-brain barrier and induces c-fos expression in rat forebrain in a manner similar to clozapine and other SGAs.

NDMC activates the M1 receptor in vivo, not just in vitro. It is unknown whether NDMC shares its parent compound’s risk for agranulocytosis. One study that measured NDMC plasma levels in patients taking clozapine found that a high NDMC:clozapine ratio predicts better enhancement of cognition in patients; however, other studies have not replicated this result. In rats, NDMC did not induce catalepsy or increase prolactin, but also only partially inhibited amphetamine-induced locomotion (a stand-in for psychosis) and inhibited conditioned avoidance response only at the highest dose of 100 mg/kg (whereas antipsychotics inhibited as early as 20 minutes).

Another study showed that NDMC did inhibit amphetamine-induced hyperactivity. NDMC was also noted to decrease errors in an eight-arm maze test (in which clozapine induced errors); this effect was reversed by an M1 antagonist. NDMC had no effect on a novel object recognition task, whereas clozapine and other antipsychotics worsened performance. Early human studies of NDMC have demonstrated safety and tolerability in oral formulation and outcomes consistent with antipsychotic actions. However, studies of this drug focused on cognitive dysfunction in schizophrenia remain to be done. NDMC appears to be a good candidate to test the therapeutic potential of M1 muscarinic stimulation on cognition in schizophrenia because of its agonist potency at the M1 and M5 receptors.”

A comprehensive functional pharmacological screen of nearly all known antipsychotics, and many of their metabolites, at a majority of the known biogenic amine G-protein-coupled receptors (GPCRs) identified NDMC as pharmacologically unique. NDMC is a potent inverse agonist of 5HT2A receptors. However, unlike any other compound tested, NDMC is a potent and efficacious muscarinic receptor agonist. Specifically, NDMC is a potent partial agonist of M1 (K,=50nM) and M5 receptors (K,=25nM). NDMC also displays agonism of M2, M3, and M4 receptors, however this interaction is 10-fold less potent than the interaction with other subtypes and indeed, under physiological conditions NDMC is able to competitively antagonize M3 receptors. In comparison, clozapine is a potent competitive antagonist of M1, M3, and M5 receptors, a weak agonist of M2 receptors, and a potent partial agonist of M4 receptors. Furthermore, olanzapine, an antipsychotic structurally related to NDMC and clozapine is an antagonist of all 5 muscarinic subtypes. Haloperidol, risperidone, and ziprasidone do not interact with any of these receptors at concentrations up to 1 μM. Thus, the agonist activity of NDMC at muscarinic receptors, particularly M1 and M5 receptors, is unique among antipsychotic drugs.

In addition to its activity at D2, 5HT2A, and muscarinic receptors, NDMC has affinity for α1, α2, D1, H1, δ2, 5HT1A, 5HT1B, 5HT3, 5HT6, and 5HT7 receptors, and Ca2+ channels in ligand binding assays. Functionally it is a potent competitive antagonist of 5HT2c, H1, and α1A receptors and an inverse agonist of 5HT6A and 5HT7A receptors.

Like clozapine, NDMC attenuates both MK-801 -induced and amphetamine-induced hyperactivity in mice at doses lower or similar to those that reduce spontaneous activity. Unlike clozapine and haloperidol, NDMC does not attenuate apomorphine-induced climbing in mice. This may reflect the reduced affinity of NDMC for D2 receptors compared to these other antipsychotics. NDMC administration results in a dose-dependent activation of mitogen-activated protein kinase (MAPK) in the CA1 region of hippocampus and this activation can be blocked by the non-selective muscarinic antagonist scopolamine. Given that M1 receptors are the predominant subtype of muscarinic receptor responsible for MAPK activation in the CA1 region of the hippocampus, this finding supports the in vivo agonism of M1 receptors by NDMC. Clozapine administration does not result in MAPK activation. Additional evidence of pharmacological activity of NDMC comes from the observation that NDMC administration increases cFOS expression in the prefrontal cortex and nucleus accumbens, but not in the striatum. The lack of cFOS expression in the striatum suggests that NDMC is unlikely to produce extrapyramidal side effects.

Muscarinic agonism on the cortex by NDMC has been disputed:

“Clozapine, an atypical antipsychotic medication that demonstrates efficacy against the positive and negative symptoms of patients with chronic and/or treatment-resistant schizophrenia (Kane et al., 1988, Meltzer, 1997 and Volavka et al., 2002), was the first atypical medication to show nootropic attributes (Hagger et al., 1993). Clozapine was found to induce mild improvements across a number of cognitive functions, including learning and memory (Bilder et al., 2002 and Meltzer and McGurk, 1999), which was eventually attributed to the drugs capacity to manipulate the muscarinic system. N-Desmethylclozapine (NDMC), the major metabolite of clozapine, was found to act as a potent M1 receptor allosteric agonist and promote the release of ACh in animal analogues of brain regions key to cognition, including the prefrontal cortex and hippocampus ( Li et al., 2005, Sur et al., 2003 and Weiner et al., 2004). It was subsequently documented that the ratio of NDMC/clozapine in the plasma of patients with schizophrenia was a better predictor of cognitive function and quality of life compared to clozapine plasma levels ( Weiner et al., 2004). This led to the hypothesis that NDMC was driving the cognitive improvements documented in patients after treatment with clozapine and could potentially be administered in isolation to help improve cognitive function.

Unfortunately it was discovered that, in contrast to its agonistic attributes in rat cortex, in human cortex NDMC acts as a M1 receptor antagonist (Thomas et al., 2010) and was documented as failing to cause any significant improvements in patient symptom severity in a double-blind, placebo-controlled phase IIB clinical trial (Anon, 2014). Despite this unfavourable NDMC finding, the muscarinic system is still considered a target for the development of novel treatments aimed at improving the symptoms of schizophrenia.” [2]

On the contrary, increasing the clozapine to norclozapine ratio via CYP1A2 inhibition has been suggested:

Increasing the clozapine: norclozapine ratio with co-administration of fluvoxamine to enhance efficacy and minimize side effects of clozapine therapy.

Although clozapine is the only antipsychotic agent to have demonstrated superior efficacy in treatment-refractory schizophrenia, one- to two-thirds of patients do not respond adequately despite acceptable dosages and plasma levels. Moreover, a significant number of patients stop the therapy for various reasons, including its side effects, many of which are thought to be related to its active metabolite, norclozapine. However, combining clozapine with the SSRI antidepressant fluvoxamine decreases norclozapine formation by inhibiting the CYP450 1A2 isoenzyme. Lowering norclozapine levels in this way while maintaining therapeutic clozapine levels increases the clozapine: norclozapine ratio; the potential benefits include both a reduction of such side effects as sedation, weight gain, metabolic disturbances, and neutropenia, and an increase in efficacy. The optimal ratio of clozapine to norclozapine has not yet been defined, but a ratio of two or more implies that saturation of clozapine metabolism has been reached. We hypothesize that co-administration of clozapine and fluvoxamine at dosages that will produce therapeutic plasma levels of clozapine and a clozapine: norclozapine ratio of two or more will increase efficacy and tolerability of clozapine therapy in treatment-resistant schizophrenic patients.

“N-desmethylclozapine (norclozapine), clozapine’s main active metabolite, is formed by the oxidative metabolism of clozapine by CYP1A2, and to a lesser extent, by CYP2C19, CYP3A4, CYP2C9, and CYP2D6. Norclozapine is also metabolized by CYP1A2. It is thought to have less antipsychotic activity than its parent compound and may be responsible for many of the side effects attributed to clozapine therapy

…some studies have found that the clozapine: norclozapine ratio can predict clinical outcome better than either the clozapine or norclozapine level alone. Norclozapine levels usually range between 65% and 90% of total clozapine levels. A clozapine: norclozapine ratio greater than two suggests that clozapine metabolism has become saturated. Several studies and case reports have shown that if norclozapine plasma levels are increased while adequate clozapine plasma levels are maintained and the clozapine: norclozapine ratio is thus increased (mainly through the use of concomitant fluvoxamine), many patients display an increased clinical response and/or decreased side effects to clozapine therapy. It should be noted, though, that at least two studies have concluded that low clozapine: norclozapine ratios are positively correlated with clinical response…

…in animal models, agonism of M1 muscarinic receptors by norclozapine has been linked to improved cognition, which may be a factor in the unique efficacy of clozapine. The decrease in norclozapine plasma levels brought on by co-administration might thus result in the loss of the cognitive benefits of clozapine therapy. One study has concluded, though, that the lower norclozapine levels generated by combined therapy, as compared to the higher levels associated with clozapine monotherapy, do not alter global functioning in schizophrenic patients…”

Higher clozapine+ norclozapine concentrations have been associated with depression-anxiety symptom dimensions: “high clozapine concentrations were associated with depression-anxiety symptoms, but the causality remains unknown.” [3]

Interestingly, diet may play a role in the metabolism of clozapine: see ‘Effect of various diets on the expression of phase-I drug-metabolizing enzymes in livers of mice.’

See also: Muscarinic Agonists for the Treatment of Cognition in Schizophrenia

Augmenting in clozapine non/partial responders

Pharmacological Augmentation Strategies for Schizophrenia Patients With Insufficient Response to Clozapine: A Quantitative Literature Review

Clozapine [also via norclozapine] has a unique pharmacological profile (below) that is extensively detailed elsewhere.clozapine

ECT is an often effective adjunct in clozapine-resistant patients [1]

One RCT (n=18) indicated that the combination of clozapine with ECT was superior to monotherapy with either clozapine or ECT alone in patients with TRS. In a recent RCT, 10 of 20 patients (50%) responded to ECT along with clozapine when using a 40% reduction in symptoms criterion, although no responders were found in the clozapine monotherapy group (n=19). Nonresponders from the clozapine group subsequently received an 8-week open trial of ECT and 47% of patients responded. Although sample sizes in these trials were small, ECT may be a promising option for the short-term treatment of patients with clozapine resistant TRS. [2]

recommendations for treatment resistant schz
From: New therapeutic approaches for treatment-resistant schizophrenia: A look to the future

From Augmentation strategies in partial responder and/or treatment resistant schizophrenia patients treated with clozapine (2014) and Schizophrenia: when clozapine fails. (2015)

Addition of atypical antipsychotics to clozapine (CLZ):

“[the] data do not support the addition of an atypical antipsychotic with high-potency D2 [blockade] to CLZ, and this is confirmed by the observation that risperidone, the SGA with the strongest D2 blockade, demonstrated poor efficacy and high risk of side effects when added to CLZ. When drugs such as aripiprazole, a partial D2 agonist, and amisulpride, a D3/5-HT7 antagonist, have been added to CLZ, a certain degree of symptoms improvement was seen, thus it seems that increasing the D2 occupation might be ineffective or deleterious rather than beneficial”

Augmentation of CLZ with amisulpride in treatment-resistant schizophrenia has been evaluated in open-label trials that reported a significant reduction of primary and secondary outcome measures. A significant improvement of residual depressive symptoms, global functioning and quality of life, but not positive and negative symptoms, was shown in a randomized, double-blind, placebo-controlled trial on a small sample of partial responder schizophrenia patients treated with CLZ; however, high rates of adverse effects, such as increase in prolactin serum levels, tremor, akathisia and bradykinesia were documented

Aripiprazole add-on to CLZ did not offer statistically significant advantage over placebo treatment for total symptom severity, although it was superior to placebo in improving negative, positive symptoms and overall clinical state, whereas no significant effect on cognitive symptoms was observed. Concerning metabolic effects, the combination of aripiprazole plus CLZ resulted in significant reduction in body weight, body mass index, fasting cholesterol and triglycerides levels

There is only limited evidence for the combination of clozapine with a second antipsychotic and no combination strategy is superior to the other.

Antidepressant augmentation

The antidepressant augmentation of CLZ remains unclear with inconsistencies reported:

– Antidepressants with predominant serotonergic effects, such as fluoxetine, have not shown beneficial effects, whereas mirtazapine and duloxetine add-on showed better results.

– Only one RCT showed that citalopram was effective on total symptoms severity.

– The positive effect reported with fluvoxamine add-on may be due to its activity towards sigma receptors or through the inhibition of CYP1A2 metabolism of CLZ, thus increasing CLZ and reducing norclozapine levels:

The increase of CLZ plasma levels might partially explain the positive effects reported with fluvoxamine augmentation; moreover, the risk of side effects also proportionally increases. Fluvoxamine added to CLZ has also been shown to decrease plasma levels of norclozapine, a toxic metabolite of CLZ, which is mainly associated with side effects, such as weight gain and metabolic syndrome in CLZ-treated patients

-Agomelatine augmentation was associated with improvement in clinical symptoms, overall psychopathological state and cognitive functioning; however, the small sample size, the lack of a control group, the open design and the non-blinded mode of rating do not allow for firm conclusions to be drawn.

In 2014, Bruno et al. conducted a 16-week, open-label, preliminary study, on 20 outpatients (9 men and 11 women) with a diagnosis of schizophrenia, who were stable on clozapine monotherapy at the highest tolerable dose (mean dose 430 mg/day) for at least one year. However, according to the Brief Psychiatric Rating Scale (BPRS) total scores >25, patients were considered partial responders to clozapine, due to the presence of residual symptoms. Concerning psychotic symptoms, at week 8, agomelatine augmentation of clozapine significantly improved Positive and Negative Syndrome Scale (PANSS) subscales “negative”, “general psychopathology”, as well as total score and overall clinical symptoms (measured by BPRS). At week 16, significant differences emerged in all PANSS domains, depressive symptoms (measured with the Calgary Depression Scale for Schizophrenia) and overall clinical symptoms. Regarding cognitive performances, at week 8, significant differences emerged only at Wisconsin Card Sorting Test (WCST) “perseverative errors”, whereas, at week 16, agomelatine treatment significantly improved performances on Stroop task and increased improvement on WCST “perseverative errors”. At endpoint, 9 subjects (64.3%) of the 14 completers responded to the coadministration of agomelatine (defined as a reduction in PANSS total score >25% between the baseline and follow-up ratings) and no patients worsened in clinical symptoms vs. baseline. The combination of agomelatine−clozapine was generally well tolerated and the most common adverse effects were gastrointestinal symptoms, headache and somnolence.

However, the small sample size, the lack of a control group, the open design, and the non-blinded mode of rating, the lack of clozapine therapeutic drug monitoring in addition to the need of longer-term, randomized, controlled studies do not allow for firm conclusions to be drawn. This may be a starting point for further research in this area as the improvement of cognitive performances in this trial was remarkable and warrants further investigations.

– See more here

Mood stabilisers:

– Lithium plus CLZ shows efficacy in schizoaffective disorder, it appears to be rather ineffective and potentially unsafe in schizophrenia

– Augmentation of valproate with CLZ has been evaluated in a single retrospective study; although it was reported as effective during the first month of treatment compared to CLZ monotherapy and CLZ associated with lithium on several symptom clusters (mood, anxiety and hostility), there is no sufficient evidence to advise the use of this augmentation strategy before further investigation in randomized clinical trials.

– Lamotrigine have shown more encouraging results, although evidence regarding its effective role in ameliorating symptoms in patients with inadequate response to CLZ is still a matter of debate.

A meta-analysis of five double-blind RCTs (total n=161), evaluating the effect of lamotrigine as an augmentor of clozapine, demonstrated that lamotrigine was superior to placebo in a total score for symptoms of psychosis (effect size=0.57,P<0.001), positive (effect size=0.34, P=0.04) and negative (effect size=0.43, P=0.008) symptoms of schizophrenia. However, two recent meta-analyses, in which an outlier study by Zoccali et al. with high effect size and small sample size was excluded, demonstrated that augmentation of clozapine with lamotrigine was not superior to placebo. Consistent with this result, Vayısog˘lu et al. found no beneficial effects of lamotrigine augmentation on psychopathology or cognitive functions in 34 patients with partial response to

See: When Clozapine is not enough: Augment with lamotrigine?


Four double-blind RCTs have investigated topiramate as an adjunct to clozapine treatment, yielding discordant results. A meta-analysis of three of these trials  found a trend towards a superior effect over placebo in reducing total symptom severity (n=89, effect size=0.75, P=0.07). However, the trend disappeared after exclusion of an outlier study by Afshar et al. with a relatively short follow-up period (8 weeks). Similar negative results of topiramate augmentation were obtained by Behdani et al. in a 17-week study in 80 patients. Topiramate augmentation of clozapine did not significantly decrease any of the three Positive and Negative Syndrome Scale (PANSS) subscales compared with placebo.


– Glutamatergic agents (glycine, D-serine, D-cycloserine etc) added to CLZ have not been effective or have worsened psychotic symptoms, suggesting that glycinergic drugs may interfere with the mechanism of action of CLZ.

NOTE: “Relative to effects in combination with typical or newer atypical antipsychotics, glycine site agonists have proved less effective when combined with clozapine. In double blind, placebo-controlled studies in which glycine (Evins et al., 2000) or D-serine (Tsai et al., 1999) has been added to clozapine, no significant beneficial response has been observed, while D-cycloserine is reported to lead to the worsening of symptoms when used in combination with clozapine (Goff et al., 1996).”

– The Ampakine CX516 showed improvement on negative symptoms and total symptom severity, although, as an experimental drug, it may not be suitable as augmentation strategy in clinical practice.

CX516, a positive modulator of the AMPA receptor, demonstrated superior efficacy for total symptom severity (effect size =1.35) and  negative symptom severity (effect size =1.43) to placebo.However, the sample size of this study was very small (n=18) and the large improvement in negative symptoms with CX516 compared with placebo appears to reflect deterioration in the placebo group; thus, these findings should be interpreted with caution.

– In a double-blind, randomized, placebo-controlled trial, the NMDA antagonist memantine add-on to CLZ was associated with a significant improvement of both positive and negative symptoms; however, results need to be interpreted with caution due to the small sample size

 In a double-blind RCT, memantine, a nonselective weak N-methyl-D-aspartate (NMDA) receptor antagonist, added to clozapine was associated with significant improvement of both positive and negative symptoms. Again, the sample size in this study was small (n=21), calling for a cautious interpretation.

– CLZ with ethyl eicosapentaenoic acid (E-EPA) has been encouraging (although controversial) thus further studies should clarify the real effectiveness and the best dose of E-EPA add-on.

EPA may be beneficial:

In one RCT, Eicosapentaenoic acid (EPA) showed better efficacy for total symptom severity than placebo in patients treated with clozapine

Estrogen may also be beneficial in women:

In a recent large-scale RCT in women with TRS (n=183), transdermal estradiol (200mcg), given as an adjunct to the ongoing antipsychotic therapy, showed superior efficacy for total symptom severity (effect size=0.31, P<0.01) and positive symptom severity (effect size=0.44, P<0.01) to placebo. Oestrogen may be a useful adjunctive treatment for women with TRS, but its therapeutic potential in men with schizophrenia remains unknown

– Minocycline add-on to CLZ  has shown promise:

Minocycline, a second-generation tetracycline characterized by anti-inflammatory and neuroprotective properties, showed beneficial effects on negative symptoms, general outcome and executive functions in a longitudinal RCT on a sample of early phase schizophrenia patients treated with SGAs, including CLZ. Recently, minocycline add-on to CLZ in two treatment-resistant schizophrenia patients was effective in reducing residual positive and negative symptoms. In both studies, minocycline was well tolerated and safe, and these results warrant further investigation of add-on treatment for patients with schizophrenia.

Non-pharmacological interventions:

Early studies with rTMS and tDCS demonstrated short-term improvements in verbal auditory hallucinations and/or negative symptoms of schizophrenia.

Barretto et al. conducted a controlled trial of CBT (n=21) in patients with clozapine-resistant TRS and found that CBT significantly improved general psychopathology compared with nonspecific psychosocial support (befriending) and that this effect persisted for 6 months. However, the sample size of this trial was small and it was not randomized. A recent meta-analysis of 12 RCTs (n=639) examining the effectiveness of CBT among outpatients with medication-resistant psychosis demonstrated beneficial effects of CBT on positive symptoms (effect size=0.47) and general symptoms (effect size=0.52)

From Clozapine augmented with glutamate modulators in refractory schizophrenia: a review and metaanalysis.

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negative symptoms.JPGA recent review found:

“…the most effective drug combinations were clozapine augmentation with 1) sodium valproate, 2) lithium, 3) amisulpride, and 4) quetiapine.”

See the next post for NMDA/glycinergic/AMPA augmentation.