Newcastle Laboratories

Clozapine and Norclozapine

Clinical Background:

Clozapine is an atypical antipsychotic used to treat schizophrenia resistant to conventional therapy. Because of the risk of agranulocytosis, white blood cell counts (WBC) are monitored weekly in t...

Clozapine is an atypical antipsychotic used to treat schizophrenia resistant to conventional therapy. Because of the risk of agranulocytosis, white blood cell counts (WBC) are monitored weekly in the early stages of therapy and monthly thereafter.
It is recommended that therapy is withheld if the WBC is less than 3,500 mm-3 and abandoned if the WBC falls below 3000 mm-3 or the granulocyte count below 1,500 mm-3. Side-effects of clozapine include lethargy, hypersalivation, constipation and somnolence. There is a risk of hypotension and seizure at higher doses. A single dose of 300-400 mg may be life-threatening in a clozapine naïve subject. Clozapine is metabolised by N-demethylation, hydroxylation and N-oxidation. The N-demethylated metabolite, norclozapine, is present in plasma at similar concentrations to the parent compound, but has a longer plasma half-life. Plasma clozapine concentrations of 0.35 mg/L and above have been associated with a good response, with the risk of convulsions increasing above 1.0 mg/L.

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Test Documents

Test Details

  • Discipline:

    Biochemistry

    Biochemistry

  • Specimen Container Adult:

    EDTA whole blood

    EDTA whole blood

  • Specimen Container Paediatric:

    EDTA whole blood

    EDTA whole blood

  • Minimum Volume Adult:

    2 mL blood

    2 mL blood

  • Minimum Volume Paediatric:

    2 mL blood

    2 mL blood

  • Special Requirement:

    Pre-dose or trough sample

    Pre-dose or trough sample

  • Transport Requirements:

    Post at ambient temperature

    Post at ambient temperature

  • Reference Ranges:

    0.35 - 0.50 mg/L

    0.35 - 0.50 mg/L

  • Other Info:

    Serum (plain tube only) or plasma samples also acceptable

    Serum (plain tube only) or plasma samples also acceptable

  • Routine Contact Name:

    Duty Biochemist

  • Routine Telephone:

    Freeman: 0191 244 8889

    RVI: 0191 282 9719

    Freeman: 0191 244 8889

    RVI: 0191 282 9719

  • Routine Email:

Availability:

Sample sent to King's College Hospital

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