Clozapine

Test ID: 

703617

CPT code:

80159

Synonyms:

Clozapine, Serum or Plasma

Clozaril®

FazaClo®

Clinical Use:

Evaluate toxicity; monitor therapeutic levels

Test Information:

Clozapine is absorbed rapidly, with peak plasma concentrations occurring within 30 minutes to six hours. Terminal half-life in humans is in the range of 5.5 to 33 hours. Determination of clozapine in plasma is needed to correlate efficacy with plasma concentration. However, pharmacogenomics and coadministration of other agents can complicate the correlation between dose and plasma concentration. Changes in the activity of the cytochrome P450 mixed-function oxidases, especially CYP1A2 and CYP3A4 can affect clozapine levels. These oxidases can be induced by drugs such as carbamazepine, with the resulting increase in activity causing 50% decrease in clozapine concentration. An additional report has indicated some patients may be ultrarapid metabolizers of clozapine due to genetically induced CYP1A2 activity levels. Conversely, clozapine plasma (serum) concentrations may be increased by inhibitors of the P450 oxidases. Amiodarone, cimetidine, ciprofloxacin, fluoxetine, fluvoxamine, indinavir, paroxetine, quinidine, ritonavir, and saquinavir are examples of inhibiting drugs which may cause increases in clozapine levels when coadministered.
A review of adverse metabolic effects has indicated clozapine can significantly increase mean levels of glucose and C-peptide, as well as increase in triglyceride levels. Additionally, the Federal Drug Administration and drug provider have issued the following: Patients being treated with clozapine must have a baseline white blood cell (WBC) count and absolute neutrophil count (ANC) before initiation of treatment as well as regular WBC counts and ANCs during treatment and for at least four weeks after discontinuation of treatment.

Specimen Type:

Serum or plasma

Requested Volume: 

1 mL

Minimum Volume: 

0.3 mL

Container Type: 

Red-top tube, lavender-top (EDTA) tube, or green-top (heparin) tube. Do not use a gel-barrier tube. The use of gel-barrier tubes is not recommended due to slow absorption of the drug by the gel. Depending on the specimen volume and storage time, the decrease in drug level due to absorption may be clinically significant.

Collection:

Transfer separated serum or plasma to a plastic transport tube.

Storage Instructions:

Room temperature

Stability Requirements:

Temperature

Period

Room temperature

14 days

Refrigerated

14 days

Frozen

14 days

Freeze/thaw cycles

Stable x3

Rejection Criteria

Gel-barrier tube

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