Drug interactions, between verapamil

McLean AJ, Knight R, Harrison PM, Harper RW. Clearance-based oral drug interaction between verapamil and metoprolol and comparison with atenolol. Am J Cardiol (1985) 55, 1628-9. 

There are reports of interactions between lithium and carbamazepine, haloperidol, digoxin, and verapamil resulting in a variety of neurotoxic and cardiotoxic effects. These are not common interactions but clearly indicate a need for caution if such drug combinations are unavoidable. Anticonvulsants... 

Multiple drug interactions have been discribed (decreased serum concentrations of phenobarbital, phenytoin, sulfinpyrazone and rifampin, increased serum concentrations of quinidine, carbamazepine, cyclosporin). Important in this setting is that a marked interaction exists between digoxin and verapamil, increasing the serum concentrations of the former due to decreased renal excretion,... 

Holtzman JL, Finley D, Mottonen L, Berry DA, Ekholm BP, Kvam DC, McQuinn RL, Miller AM. The pharmacodynamic and pharmacokinetic interaction between single doses of flecainide acetate and verapamil effects on cardiac function and drug clearance. Clin Pharmacol Ther 1989 46(l) 26-32. 

Because finasteride and dutasteride are metabolized primarily by CYP3A4, the CYP3A4 inhibitors, such as ritonavir, ketoconazole, verapamil, diltiazem, cimetidine, and ciprofloxacin, may increase the drugs blood levels and, possibly, cause drug-drug interactions. Clinical drug interaction studies have shown no pharmacokinetic or pharmacodynamic interactions between dutasteride and tamsulosin or terazosin, warfarin, digoxin, and cholestyramine. 

Wayne VS, Harper RW, Laufer E, Federman J, Anderson ST, Pitt A. Adverse interaction between beta-adrenergic blocking drugs and verapamil-report of three cases. Aust N Z J Med (1982) 12, 285-9. 

Evidence for a direct correlation between the turnover number for vinblastine-stimulated ATP hydrolysis and vinblastine transport rate was provided by Ambudkar and Stein [43]. Since compounds that interact with P-gp often exhibit a high lipid-water partition coefficient and can cross the lipid bilayer by passive diffusion, the stoichiometry between ATP hydrolysis and drug transport is difficult to assess. Using a permanently charged spin-labeled analogue of verapamil that cannot cross the membrane by passive diffusion [44], a direct correlation between ATP hydrolysis and drug transport was demonstrated [45]. 

How are these allosteric interactions brought about between the different classes of calcium channel blocking drugs Verapamil increases the dissociation constant (ATD) for binding of [3H]nitrendipine [91, 102, 127, 132] that is, the affinity of the binding site for [3H]nitrendipine is reduced. This reduced... 

No clinically relevant interactions appear to occur between sildenafil, tadalafil or vardenafil and most antihypertensive drugs. The exceptions may be diltiazem and verapamil. The potentially serious interactions of sildenafil, tadalafil and vardenafil with the alpha blockers and nitrates are discussed elsewhere. See Phosphodiesterase type-5 inhibitors + Alpha blockers , p.l268 and Phosphodiesterase type-5 inhibitors -I- Nitrates , p.l272. 

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