Sildenafil citrate, the citrate salt of sildenafil, is a phosphodiesterase type 5 (PDE5) inhibitor used as an active pharmaceutical ingredient (API) in medications for erectile dysfunction (e.g., Viagra) and pulmonary arterial hypertension (e.g., Revatio). It works by enhancing blood flow through vasodilation in targeted tissues, particularly in the corpus cavernosum and pulmonary vasculature.

In pharmaceutical research, it serves as a reference compound for developing PDE5 inhibitor analogs with optimized pharmacokinetics, such as improved bioavailability, longer half-life, or reduced side effects. It is also employed in preformulation and formulation studies to evaluate stability, solubility (pH-dependent, better in acidic conditions), and compatibility with excipients for oral solid dosage forms like tablets and capsules.

As a specialty chemical, it is produced under strict GMP conditions for clinical and commercial use, with applications extending to investigational studies on novel delivery systems, including targeted nanoparticles for enhanced efficacy and specificity.