Advanced spectrophotometric methods for quantitative assessment of two antihypertensive drugs in mixture with hydrochlorothiazide in pure form and pharmaceutical formulations

Labetalol (Lab) and nebivolol (Neb) are β-adrenoceptor blocking agents that are employed for control of hypertension alone or co-administered with hydrochlorothiazide (HCTZ) as a potent diuretic for synergistic antihypertensive effect. Advanced, accurate and simple spectrophotometric methods with minor manipulation of zero-order spectra were suggested for simultaneous quantitation of Lab or Neb in mixture with HCTZ for quality control purpose in pure form and pharmaceutical formulations. These methods include (a) constant center method, (b) advanced absorbance subtraction method for Lab and HCTZ, (c) absorption factor method (AFM) and (d) the ratio subtraction method. The established methods were successfully applied over concentration ranges 10–100 µg/mL, 10–75 µg/mL and 2.5–25 µg/mL of Lab, Neb and HCTZ, respectively. Results were compared statistically to those of official and reported methods revealing no remarkable difference. Validation of methods followed international conference of harmonization guidelines. Suggested methods require minor processing of zero-order spectra with accurate results that facilitate the quantitative estimation of studied mixtures in quality control laboratories.