Clozapine (Clz), an atypical antipsychotic, is the reference medication for patients with treatment-resistant schizophrenia. Due to the high inter-individual variability of its pharmacokinetics and its narrow therapeutic index, a close therapeutic drug monitoring (TDM) of Clz is highly recommended.

Several factors can cause a variation in the pharmacokinetics as age, smoking habits, coffee consumption and drug interaction. Genetic factors related to hepatic expression levels of the cytochrome P450 (CYP), regulate the hepatic clearance of Clz, thereby determine its bioavailability.

The CYP1A2 and CYP2C19 isoenzymes are mainly responsible for the metabolism of several drugs including Clz. It has been demonstrated that there is an interethnic variation in the expression and function of these two isoenzymes. This variation is caused by single nucleotide polymorphisms (SNPs) of genes encoding these proteins.

While the Influence of the different polymorphisms related to CYP1A2 and CYP2C19 have been established especially in Asian and Caucasian populations, no study has examined the impact of these SNPs in the southern Mediterranean populations. Moreover, the impact of these SNPs is very controversial. The present study aims to investigate in Tunisian schizophrenic patients, the influence of genetic (CYP1A2 and CYP2C19 polymorphisms) and non-genetic factors on Clz pharmacokinetics.

Inclusion Criteria:

• Schizophrenic patients receiving clozapine
• Good adherence to the treatment (clozapine)

Exclusion Criteria:

• Patients who were co-prescribed drugs that affected the pharmacokinetics of Clozapine.
• Patients who presented gastrointestinal disorders disturbing absorption of clozapine.