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Fluoxetine

Fluoxetine is a selective serotonin reuptake inhibitor approved for treatment of bulimia, obsessive-compulsive behavior, panic, premenstrual dysphoria, and major depressive disorder. Both fluoxetine and its major metabolite, norfluoxetine, are pharmacologically active. Due to the long half-lives of parent and metabolite (1-6 days), it may take several weeks for patients to reach steady-state concentrations. Significant interindividual variability in fluoxetine pharmacokinetics has been reported. Fluoxetine is a potent inhibitor of CYP2D6 and is subject to numerous drug interactions.

The most common side effects of fluoxetine therapy include nausea, nervousness, anxiety, insomnia, and drowsiness. Anticholinergic and cardiovascular side effects are markedly reduced compared to tricyclic antidepressants. Fatalities from fluoxetine overdose are extremely rare.

Therapeutic drug monitoring is useful when patients are taking other medications that may be inhibitory, dose or formulation changes, and assessment of compliance Since both fluoxetine and its metabolite are pharmacologically active, both concentrations should be measured. Fluoxetine and norfluoxetine are measured by liquid chomatography/tandem mass spectrometry. Most individuals respond optimally when combined serum concentrations for both parent and metabolite are in the therapeutic range of 120-300 ng/mL. A toxic range has not been well established.

Specimen requirement is a red top tube of blood.

References

Wille SM, Cooreman SG, Neels, HM, Lambert WE: Relevant issues in the monitoring and toxicology of antidepressants. Crit Rev Clin Lab Sci 2008;45(1):25-89

Baumann P, Hiemke C, Ulrich S, et al: The AGNP-TDM expert group consensus guidelines: therapeutic drug monitoring in psychiatry. Pharmacopsychiatry 2004;37:243-265

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