Clozapine, Serum or Plasma

Casandra

Casandra Test Code LC72959Version 1 (DRAFT)

Performing Lab

Lab LabcorpLab Test ID 706440CPT Code 80159

Clozapine, Serum or Plasma

Clinical Use

Use

Clozapine is used primarily to evaluate toxicity and monitor therapeutic levels in patients. It is essential for correlating the efficacy of the drug with plasma concentration, particularly as the drug is absorbed rapidly with peak plasma concentrations occurring within 30 minutes to six hours. Therapeutic drug monitoring is crucial due to the variable metabolism of clozapine, which can be influenced by pharmacogenomics and coadministration of other agents that affect CYP1A2 and CYP3A4 activity, potentially leading to significant changes in drug levels.

Special Instructions

Patients treated with clozapine must have baseline white blood cell (WBC) count and absolute neutrophil count (ANC) before starting treatment and regularly during therapy and at least four weeks after discontinuation. The specimen should be collected using a red-top, lavender-top (EDTA), or green-top (heparin) tube. Transfer separated serum or plasma to a plastic transport tube. Avoid gel-barrier tubes as they can absorb the drug, affecting levels.

Limitations

The test has not been cleared or approved by the Food and Drug Administration. Pharmacogenomics and coadministration of other agents can complicate the dose and plasma concentration correlation. Cytochrome P450 oxidases, especially CYP1A2 and CYP3A4, can significantly influence clozapine levels. Enzyme inducers, like carbamazepine, can lead to decreased clozapine concentration, while inhibitors like amiodarone, fluvoxamine, and others may increase levels.

Test Details