Viagra Hair and Skin Changes: What Sildenafil Actually Does to Your Body

What sildenafil does in the body

Viagra is a phosphodiesterase type 5 (PDE5) inhibitor indicated for erectile dysfunction [1]. During sexual stimulation, nitric oxide released in the corpus cavernosum raises cyclic GMP, which relaxes smooth muscle and lets blood flow in; sildenafil blocks the enzyme that breaks cyclic GMP down, so that response is stronger [1]. It has no effect without sexual stimulation and no direct relaxant effect on isolated corpus cavernosum tissue [1].

The label describes sildenafil as having systemic vasodilatory properties: a single 100 mg dose lowered supine blood pressure in healthy volunteers by a mean maximum of about 8.4/5.5 mm Hg [1]. Flushing is the skin reaction most often recorded in the trials [1].

Flushing: how common, and at which dose

In the fixed-dose trials that support approval, flushing was reported by 10% of men taking 25 mg, 19% taking 50 mg and 18% taking 100 mg, against 2% of men on placebo [1]. The 100 mg group did not report more flushing than the 50 mg group in that table, so flushing is not a clean dose ladder. In the flexible-dose trials, which reflect how the drug is usually prescribed, flushing was reported by 10% of men on sildenafil versus 1% on placebo [1].

After a fasting dose, sildenafil reaches peak blood levels in 30 to 120 minutes, with a median of 60 minutes, and its terminal half-life is about 4 hours [1]. A high-fat meal delays the peak by about 60 minutes and cuts peak concentration by 29% [1]. The label gives the usual dose as 50 mg as needed about 1 hour before sexual activity, adjustable to 25 or 100 mg, with a maximum of once per day [1]. It says to consider a 25 mg starting dose for men over 65, men with liver impairment, men with severe kidney impairment (creatinine clearance below 30 mL/min), men taking strong CYP3A4 inhibitors or erythromycin, and men starting while stable on an alpha-blocker [1].

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Rash and other skin reactions in the label

Rash is the second skin entry in the fixed-dose tables: 1% at 25 mg, 2% at 50 mg and 3% at 100 mg, against 1% on placebo [1]. In the flexible-dose trials rash was reported by 2% on sildenafil and 1% on placebo [1].

The label also lists reactions that occurred in under 2% of trial patients, where a causal relationship to sildenafil is uncertain. The skin entries in that list are urticaria, herpes simplex, pruritus, sweating, skin ulcer, contact dermatitis and exfoliative dermatitis; photosensitivity reaction appears in the general list of uncommon events [1]. Known hypersensitivity to sildenafil is a contraindication, and the label notes that hypersensitivity reactions including rash and urticaria have been reported [1].

In placebo-controlled studies, 2.5% of patients taking Viagra stopped because of adverse reactions, compared with 2.3% taking placebo [1]. More than 3,700 patients received Viagra in premarketing trials [1].

Hair loss: what the label shows

Hair loss does not appear in the Viagra label's fixed-dose table, its flexible-dose table, or its list of less common reactions [1]. The label also carries a post-marketing section, which is built from voluntary reports of uncertain population size; the label states that frequency and causality cannot be reliably estimated from such reports [1].

Viagra is indicated only for erectile dysfunction [1].

Drug and alcohol interactions that affect blood pressure

Nitrates. Nitrates and nitrites in any form, taken regularly or intermittently, are contraindicated with sildenafil because it potentiates their blood-pressure-lowering effect [1]. The label says it is unknown when nitrates can be given safely after a dose of Viagra: sildenafil levels at 24 hours are much lower than the peak, but the label states it is unknown whether nitrates are safe at that point [1].

Alpha-blockers. Sildenafil and alpha-blockers both lower blood pressure, and the effect is additive. The label says patients should be stable on the alpha-blocker before starting sildenafil, and that sildenafil should be started at 25 mg [1]. In a doxazosin study, sildenafil 25 mg produced a placebo-subtracted maximum standing systolic fall of 6.0 mm Hg, and one of the four men given 100 mg had severe postural hypotension [1].

Amlodipine. Sildenafil 100 mg with amlodipine 5 or 10 mg in hypertensive patients added a mean 8/7 mm Hg fall in supine blood pressure [1].

CYP3A4 inhibitors. Ritonavir raised sildenafil AUC 11-fold, and the label says not to exceed a single 25 mg dose in a 48-hour period with ritonavir [1]. Erythromycin raised peak concentration 160% and AUC 182%; saquinavir raised them 140% and 210%; the label advises considering a 25 mg starting dose with either [1].

Alcohol. Sildenafil 50 mg given with alcohol to a mean peak blood alcohol of 0.08% did not potentiate alcohol's blood-pressure-lowering effect in healthy volunteers [1].