ABSTRACT
INTRODUCTION: Sildenafil (Viagra®) is a selective phosphodiesterase type 5 (PDE5) inhibitor that block the breakdown of cyclic guanyl monophosphate (cGMP) leading to relaxation of the smooth muscles of the corpus cavernous and an increase in blood flow resulting in penile erection. It is hypothesized that sildenafil will increase the release of oxygen from erythrocytes and shift the oxygen-hemoglobin curve to the right. AIM: The aim of this study was to investigate the effect of varying doses of sildenafil on the p50 of the oxygen-hemoglobin dissociation curve in blood samples from eight (8) healthy adult male volunteers with normal hemoglobin HbAA. METHOD: The hemox-analyzer was used to generate the p50 and the oxygen-hemoglobin dissociation curves. MAIN OUTCOME MEASURES: The effect of different doses of sildenafil on the p50 values and shift of the oxygen-hemoglobin curve were the main outcome measures. RESULT: Sildenafil caused a statistically significant increase in the p50 values and rightward shift of the oxygen-hemoglobin dissociation curve. CONCLUSION: Sildenafil caused a dose-dependent increase in the release of oxygen from the erythrocytes as shown by the increased p50 values and rightward shift of the oxygen-hemoglobin dissociation curve. Ellis SS and Pepple DJ. Sildenafil increases the p50 and shifts the oxygen-hemoglobin dissociation curve to the right.