<p><strong>Cytochrome P450 Isozymes</strong>: Doxepin is primarily metabolized by hepatic cytochrome P450 isozymes CYP2C19 and CYP2D6, and to a lesser extent, by CYP1A2 and CYP2C9. Inhibitors of these isozymes may increase the exposure of doxepin. Doxepin is not an inhibitor of any CYP isozymes at therapeutically relevant concentrations. The ability of Doxepin to induce CYP isozymes is not known.<br />
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<strong>Cimetidine</strong>: Doxepin exposure is doubled with concomitant administration of cimetidine, a nonspecific inhibitor of CYP isozymes. A maximum dose of 3 mg is recommended in adults and elderly when cimetidine is co administered with Doxepin.<br />
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<strong>Alcohol</strong>: When taken with Doxepin, the sedative effects of alcohol may be potentiated.<br />
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<strong>CNS Depressants and Sedating Antihistamines</strong>: When taken with Doxepin, the sedative effects of sedating antihistamines and CNS depressants may be potentiated.<br />
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<strong>Tolazamide</strong>: A case of severe hypoglycemia has been reported in a type II diabetic patient maintained on tolazamide (1 g/day) 11 days after the addition of oral doxepin (75 mg/day).</p>