Physicochemical and Spectroscopic Characterization of Some Selected Antihypertensive Drug Candidates for the Bilayer Tablet

Abstract

Hypertension is a major global public health concern and one of the leading causes of cardiovascular morbidity and mortality. The present work focuses on the preliminary characterization and formulation rationale for the development of a bilayer antihypertensive tablet containing an immediate-release layer of Hydrochlorothiazide (HCTZ) and a sustained-release layer of either Enalapril or Lisinopril. Comprehensive preformulation studies were carried out to evaluate the physicochemical properties of the selected active pharmaceutical ingredients. Organoleptic characteristics, melting point, solubility, partition coefficient (Log P), pKa, ultraviolet (UV) spectroscopy, Fourier Transform Infrared (FT-IR) spectroscopy, drug–excipient compatibility, and powder flow properties were investigated to establish the identity, purity, stability, and suitability of the drugs for bilayer tablet formulation. The characterization studies confirmed that all three drugs complied with pharmacopeial specifications and exhibited physicochemical properties appropriate for oral solid dosage form development. Overall, the findings support the feasibility of developing a bilayer tablet containing an immediate-release Hydrochlorothiazide layer and a sustained-release ACE inhibitor layer as a novel antihypertensive drug delivery system. The present preformulation studies establish a strong scientific foundation for subsequent formulation optimization, characterization, and in vitro evaluation of the proposed bilayer tablet.