Effects of nicorandil and verapamil, antianginal agents, on plasma digoxin concentrations in rats and dogs

Evaluation of the effect of isobutyl paraben and 2-ethyl hexyl paraben on p-glycoprotein functional expression in rats: a pharmacokinetic study

BACKGROUND

Pharmaceutical excipients have been shown to influence drug disposition through modulating transport protein.

OBJECTIVES

This study assessed the effect of single dose administration of parabens on the pharmacokinetics (PK) of digoxin, a probe substrate of p-glycoprotein (p-gp), in vivo. Also, the effect of multiple dosing of parabens on p-gp expression was examined.

METHODS

Rats were randomized into four groups that received either the vehicle, 25mg/kg verapamil, 100mg/kg isobutyl paraben, or 100mg/kg 2-ethyl hexyl paraben, which was followed by giving 0.2mg/kg digoxin via oral gavage. Blood samples were collected at different time points, digoxin concentration was measured using LC/MS-MS, and digoxin PK parameters were estimated. Another set of rats received multiple doses of parabens for 14 days which was followed by measuring intestinal and hepatic mRNA expression of p-gp using qRT-PCR.

RESULTS

Single dose administration of verapamil significantly increased Cmax (by 60.4%) and AUC0-t (by 61.7%) of digoxin compared to the control group, while the PK parameters of digoxin in rats exposed to parabens were not significantly different from the control. Consistently, the mRNA expression of p-gp in intestine and liver was not affected by parabens treatment.

CONCLUSIONS

The lack of isobutylparaben and 2-ethylhexyl paraben effect on p-gp may suggest the insignificant interaction of parabens with p-gp drug substrates, which could be of safety considerations when designing pharmaceutical formulations.

Pharmacology and therapeutic effects of nicorandil

Nicorandil, a nicotinamide derivative, is an orally efficacious antianginal drug possessing a nitrate moiety in its chemical structure. This drug is an effective and well-tolerated treatment for various types of angina pectoris. Its general efficacy is similar to that of nitrates, with several unique effects on the cardiovascular system. Nicorandil causes sustained dilation of both the arterial resistance and conductive vessels, thus markedly dilating the coronary artery and increasing coronary blood flow. In addition, nicorandil, unlike nitroglycerin or isosorbide dinitrate, possesses little hemodynamic effect on heart rate, blood pressure, or cardiac contractility with clinical doses yielding antianginal effects. The mechanism causing coronary vasodilation has not been completely clarified but appears to be associated partly with increases in c-GMP, as well as the hyperpolarization of the smooth muscle membrane. Nicorandil, in single oral doses of 10-30 mg, has been shown to be effective in chronic stable angina, as assessed objectively by increases in exercise duration and/or the time to onset of ST-segment depression during treadmill exercise. In open studies and controlled efficacy evaluations, nicorandil in daily oral doses of 15-40 mg demonstrated significant effectiveness in the treatment of various types of angina pectoris. Headaches due to vasodilation may occur, and some side effects occurred in 5.1-34% of patients receiving nicorandil, but were generally minor in nature. There was no depressant effect on atrioventricular conduction, which occurs frequently in patients treated with calcium antagonists of the verapamil and diltiazem type. Nicorandil may be effective even in patients with rest and effort angina who do not respond to combination therapy with calcium antagonists and oral nitrates. Thus, nicorandil appears to be a valuable addition to the arsenal of antianginal drugs due to its low incidence of serious side effects.

Effects of AN-132 and quinidine, antiarrhythmic agents, on plasma digoxin concentrations in rats

The effects of AN-132, 3-(diisopropylaminoethyl-amino)-2',6'-dimethylpropionanilide.2H 3PO4, on chloroform-induced arrhythmias and plasma digoxin concentrations have been compared with those of quinidine in rats. AN-132 (0.01-3 mg kg-1) administered orally significantly inhibited the incidence of cardiac arrhythmias in a dose-related fashion. A single dose of digoxin (1 mg kg-1) given orally for 7 consecutive days was followed, on day 8, orally by digoxin alone, or together with AN-132 (50, 100 and 200 mg kg-1) or quinidine (25 and 50 mg kg-1). The AUC0-24 and Cmax of plasma digoxin were enhanced significantly by co-administration of quinidine, but not by AN-132.