AMIODARONE - plasma or serum

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Specimen: 5 mL blood in lithium heparin or plain tube. Gel tubes should not be used. The specimen should be collected £4 hours after the last dose.

Method: HPLC. Some laboratories measure an active metabolite, desethylamiodarone.

Therapeutic Interval: 1.5-3.9 mmol/L (1.0-2.5 mg/L).

Application: Monitoring amiodarone therapy.

Interpretation: The drug has an elimination half-life of approximately 40 days, so reassessment after a change in dose should not be done for approximately 3 months. Toxic effects may not become evident for some months after therapy is commenced (or altered) and can occur with levels within the therapeutic interval. TSH should be measured intermittently in all patients, as the drug can cause hypothyroidism or hyperthyroidism.

Reference: Freedman MD and Somberg JC. J Clin Pharmacol 1991; 31: 1061-1069.

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