Clozapine – Mechanism of Action
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Clozapine has a mechanism of action that is unique to other second generation antipsychotics. (SGAs)
- Clozapine is a dopamine and serotonin antagonist (5HT2A) with a few unique differences compared to other SGAs.
- Clozapine has much higher antagonistic activity on cortical and limbic dopamine D4 than D2 receptors.
- It also antagonizes 5HT2 serotonergic receptor subtypes (5HT2A & 5HT2C) and adrenergic (α1), histamine (H1), and muscarinic receptors (M1).
- The combination of relatively high D1, low D2, and very high 5-HT2 receptor occupancy rates is unique to Clozapine and may explain its lower propensity for Extrapyramidal side effects.
- Clozapine is hypothesised to have some anti-inflammatory properties as demonstrated in rats exposed to an inflammatory challenge, with response measured through activated microglia. Clozapine administration reversed microglial activation and iNOS increase, but not the alterations of oxidative stress parameters. [Ribeiro B et al.,2013 ]
- Clozapine and its two major metabolites, clozapine-N-oxide (CNO) and N-desmethylclozapine (NDC) exhibit neuroprotective and anti-inflammatory properties. [Regen F et al., 2020]
- Endogenous retinoid acid (RA) signalling is involved in the pathophysiology of schizophrenia. Patients with schizophrenia have lower levels of all-trans RA; at-RA (The biologically most active metabolite of vitamin A). Clozapine and its metabolites potently inhibit RA catabolism thus increasing levels of at-RA. [Regen F et al., 2020]
- Clozapine is also postulated to increase the GABAergic neuroactive steroid (NS) allopregnanolone which has anxiolytic and antidepressant properties.[Marx C et al., 2006]; [Zorumski C et al., 2013]