Calcium channel blockers metabolism

Carbamazepine [P] Decreased carbamazepine metabolism with diltiazem and verapamil possible increase in calcium channel blocker metabolism. 

Hypertension Calcium channel blockers ACE inhibitors ARBs Diltiazem, verapamil inhibit CSA/TAC metabolism Dihydropyridines may potentiate CSA-gingival hyperplasia May exacerbate hyperkalemia monitor K+, SCr to assess for renal allograft vascular disease may be useful in posttranplant erythrocytosis (hematocrit greater than 55%)... 

Ma, B., Prueksaritanont, T. and Lin, J.H. (2000) Drug interactions with calcium channel blockers possible involvement of metabolite-intermediate complexation with CYP3A. Drug Metabolism and Disposition, 28 (2), 125-130. 

Cytochrome P450 inhibition Coadministration of delavirdine tablets with certain nonsedating antihistamines, sedative hypnotics, antiarrhythmics, calcium channel blockers, ergot alkaloid preparations, amphetamines, and cisapride may result in potentially serious or life-threatening adverse events caused by possible effects of delavirdine on the hepatic metabolism of certain drugs metabolized by CYP3A and... 

The calcium channel blockers are orally active agents and are characterized by high first-pass effect, high plasma protein binding, and extensive metabolism. Verapamil and diltiazem are also used by the intravenous route. 

Verapamil, diltiazem, and perhaps nicardipine (but not nifedipine) inhibit hepatic drug-metabolizing enzymes. Metabolism of diltiazem, nifedipine, verapamil, and probably other calcium channel blockers subject to induction and inhibition. 

Cimetidine [NP] Decreased metabolism of calcium channel blockers. 

A similar phenomenon has been observed with the well-established mechanism-based inhibitor, diltiazem (108). Diltiazem (Cardizem SR , 120 mg b.i.d. for 7 days) caused a decrease in small bowel CYP3A activity of 62% with no corresponding change in intestinal CYP3A mRNA or protein expression. Many clinical studies have shown that diltiazem, a calcium channel blocker, inhibits the metabolism of CYP3A substrates, such as triazolam (109), midazolam (110), and... 

In contrast, decreases in theophylline metabolism by selective inhibitors of CYP1A2, such as fluvoxamine and some quinolone antibiotics, or by selective and potent inhibitors of CYP3A4, such as the macrolide antibiotics, have resulted in serious theophylline toxicity (22). It is postulated that taken over time, the macrolide antibiotics act as mechanism-based inhibitors of CYP isoforms other than just CYP3A4. Some nonselective inhibitors of P450s, such as cimetidine, some p-blockers and calcium channel blockers, and others (19,22), also appear to inhibit the metabolism of theophylline enough to cause toxicity. 

---