After a 150-mg dose, the half-life of CMI ranges from 19 hours to 37 hours (mean, 32 hr) and that of DMI ranges from 54 hours to 77 hours (mean, 69 hr). Steady-state levels after multiple dosing are typically reached within 7 to 14 days for CMI. Plasma concentrations of the metabolite exceed the parent drug on multiple dosing. After multiple dosing with 150 mg/day, the accumulation factor for CMI is approximately 2.5 and for DMI is 4.6. Importantly, it may take two weeks or longer to achieve this extent of accumulation at constant dosing because of the relatively long elimination half-lives of CMI and DMI (see DOSAGE AND ADMINISTRATION). The effects of hepatic and renal impairment on the disposition of Anafranil have not been determined.

Interactions - Co-administration of haloperidol with CMI increases plasma concentrations of CMI. Co-administration of CMI with phenobarbital increases plasma concentrations of phenobarbital (see PRECAUTIONS: DRUG INTERACTIONS). Younger subjects (18 to 40 years of age) tolerated CMI better and had significantly lower steady-state plasma concentrations, compared with subjects over 65 years of age. Children under 15 years of age had significantly lower plasma concentration/dose ratios, compared with adults. Plasma concentrations of CMI were significantly lower in smokers than in nonsmokers.

Animal Toxicology

Phospholipidosis and testicular changes, commonly associated with tricyclic compounds, have been observed with Anafranil. In chronic rat studies, changes related to Anafranil consisted of systemic phospholipidosis, alterations in the testes (atrophy, mineralization) and secondary changes in other tissues. In addition cardiac thrombosis and dermatitis/keratitis were observed in rats treated for 2 years at doses which were 24 and 10 times the maximum recommended human daily dose (MRHD), respectively, on a mg/kg basis, and 4 and 1.5 times the MRHD, respectively, on a mg/m² basis.

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