Fluvoxamine increases the clozapine serum levels significantly

Area of Science:

• Pharmacology
• Psychiatry
• Clinical Toxicology

Background:

• Clozapine is an atypical antipsychotic used for treatment-resistant schizophrenia.
• Fluvoxamine is a selective serotonin reuptake inhibitor (SSRI) antidepressant.
• Drug interactions can alter the efficacy and safety of psychiatric medications.

Observation:

• Two physically healthy patients with paranoid schizophrenia were treated with clozapine.
• Fluvoxamine was co-administered to both patients.
• Significant elevations in clozapine serum levels were observed.

Findings:

• The co-administration of fluvoxamine with clozapine resulted in a 5-10 fold increase in clozapine serum concentrations.
• This interaction suggests a pharmacokinetic mechanism, likely involving inhibition of clozapine metabolism by fluvoxamine.

Implications:

• Clinicians must be vigilant for potential clozapine toxicity when initiating or adjusting fluvoxamine dosage in patients on clozapine.
• Therapeutic drug monitoring of clozapine levels is recommended during co-administration.
• Dosage adjustments of clozapine may be necessary to mitigate the risk of adverse events associated with elevated serum levels.