Development and validation of alternative methods by non-aqueous acid-base titration and derivative ultraviolet spectrophotometry for quantification of sildenafil in raw material and tablets

Sildenafil citrate (SILC) is a potent phosphodiesterase-5 inhibitor used for erectile dysfunction and pulmonary hypertension. This study shows two simple, fast and alternative analytical methods for SILC determination by non-aqueous titration and by derivative ultraviolet spectrophotometry (DUS) in active pharmaceutical ingredient and/or dosage forms. The quantitation method of SILC active pharmaceutical ingredient by non-aqueous acid-base titration was developed using methanol as solvent and 0.1 mol/L of perchloric acid in acetic acid as titrant. The endpoint was potentiometrically detected. The non-aqueous titration method shows satisfactory repeatability and intermediate precision (RSD 0.70-1.09%). The neutralization reaction occurred in the stoichiometric ratio 1:1 in methanol. The determination of SILC active pharmaceutical ingredient or dosage forms by DUS was developed in the linear range from 10 to 40 µg/mL, in 0.01 mol/L HCl, using the first order zero-peak method at λ 256 nm. The DUS method shows selectivity toward tablets excipients, appropriate linearity (R2 0.9996), trueness (recovery range 98.86-99.30%), repeatability and intermediate precision in three concentration levels (RSD 1.17-1.28%; 1.29-1.71%, respectively). Therefore, the methods developed are excellent alternatives to sophisticated instrumental methods and can be easily applied in any pharmaceutical laboratory routine due to simple and fast executions.

Vasodilatadores orales en la insuficiencia cardíaca / Oral vasodilators in heart failure

Oral vasodilators have proved to be valuable drugs in the management of systolic or diastolic heart failure. They produce a clinical and hemodynamic relief of preload, afterload or both during the resting state or exercise. Although left ventricular hypertrophy is an adaptative response to myocardial stress, in the long run it becomes an independent risk factor leading to diastolic dysfunction. At present, pharmacological regression of ventricular hypertrophy has a prognostic importance. Of the large number of available vasodilators, angiotensin converting enzyme inhibitors have proved to be the most succesful drugs. They behave as afterload relievers, counteracting both the renin-angiotensin and adrenergic systems, but also are powerful inhibitors of cardiomyocite enlargement and interstitial connective tissue proliferation. This last structural change may revert the compromised diastolic function of the heart