Development and Validation of a Novel Bioanalytical RP-HPLC Method for the Simultaneous Estimation of Nifedipine and Telmisartan in Rat Plasma: Application to Pharmacokinetic Studies

A simple, sensitive, and cost-effective bioanalytical method using reverse-phase high-performance liquid chromatography with UV detection was developed and validated for the simultaneous estimation of nifedipine and telmisartan in rat plasma. The protein precipitation technique was used for sample preparation, and isocratic elution was performed using acetonitrile, methanol, and phosphate buffer (60:20:20, v/v; pH 3.0) as the mobile phase. The analytes were separated using a C18 column and detected at a wavelength of 252 nm. The method was validated according to US FDA guidelines, demonstrating selectivity, linearity, accuracy, precision, recovery, and stability. The calibration curves were linear over the concentration ranges of 5-300 ng/mL for nifedipine and 10-600 ng/mL for telmisartan. The intra- and inter-day precision and accuracy were within the acceptable limits. The mean extraction recoveries were approximately 94% for both analytes, with no significant matrix effects. The validated method was successfully applied in a pharmacokinetic interaction study in Wistar rats. The pharmacokinetic parameters of nifedipine and telmisartan, alone and in combination, were determined using non-compartmental analysis. The results revealed no significant drug-drug interactions between nifedipine and telmisartan, suggesting their potential for use in fixed-dose combinations in patients with cardiovascular disease. This study provides a reliable bioanalytical method and pharmacokinetic evidence to support the rational use of nifedipine and telmisartan in combination therapy for hypertension.