Cimetidine CYP450 inhibition

Fluoxetine, paroxetine, bupropion, duloxetine, and other CYP450 2D6 inhibitors may increase TCA concentrations Cimetidine may increase plasma concentrations of TCAs and cause anticholinergic symptoms Phenothiazines or haloperidol may raise TCA blood concentrations May alter effects of antihypertensive drugs may inhibit hypotensive effects of clonidine Use of TCAs with sympathomimetic agents may increase sympathetic activity Methylphenidate may inhibit metabolism of TCAs... 

Drug interactions Cimetidine is a CYP450 inhibitor and can inhibit the metabolism of phenytoin, warfarin, and theophylline. Famotidine, nizatidine, and ranitidine are unlikely to cause clinically significant drug interactions. All antagonists have the potential to interact with other drugs that require gastric acid for absorption (e.g., ketoconazole, itraconazole). 

Drug Interactions. Phenobarbital is a potent enzyme inducer and may increase the elimination of any drug metabolized by CYP450-or UGT-mediated metabolism. Valproic acid, phenytoin, felbamate, cimetidine, and chloramphenicol inhibit phenobarbital metabolism, necessitating a decrease in dose. Ethanol increases the metabolism of phenobarbital. ... 

Warfarin Cimetidine R t S Inhibition of hepatic CYP450 isoenzymes Unclear 47... 

As discussed above, the analgesic effect of codeine depends greatly on its abihty to be metabolized to morphine. In patients in whom large amounts of codeine have been administered without relief, the possibility of a polymorphism of the CYP2D6 enzyme must be considered. Medications that inhibit CYP2D6 may reduce or even completely block the conversion of codeine to morphine. These include selective serotonin reuptake inhibitors (SSRls), cimetidine, and antidepressants such as buproprion. On the other hand agents that induce CYP450 isozymes, such as rifampin and dexamethasone, increase the conversion rate and increase the risk of adverse events. 

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