RECENT MAJOR CHANGES

Cyclic guanosine monophosphate causes smooth muscle relaxation in the corpus cavernosum thereby allowing inflow of blood; the exact mechanism by which cGMP stimulates relaxation of smooth muscles has not been determined. PDE5 is responsible for degradation of cGMP in the corpus cavernosum.

• The onset of action is usually within 30 minutes.
• Peak effect occurs around 1 hour after ingestion.
• The duration of action can last up to 4-6 hours.

Sildenafil enhances the effect of NO by inhibiting PDE5 thereby raising concentrations of cGMP in the corpus cavernosum.

Usual Geriatric Dose for Erectile Dysfunction

Coadministration of saquinavir increased the sildenafil AUC by about 3-fold in a drug interaction study. Silodosin: (Moderate) Due to the potential for symptomatic hypotension, patients should be stable on silodosin therapy before initiating therapy with the lowest dose of sildenafil. Conversely, patients already receiving an optimized dose of sildenafil should be started on the lowest dose of silodosin; increases in the alpha-blocker dose should be done in a stepwise fashion. Other variables, such as intravascular volume depletion, concurrent antihypertensive therapy, or evidence of hemodynamic instability with alpha-blocker monotherapy, may affect the safety of concomitant use of sildenafil and silodosin. Sodium Phenylbutyrate; Taurursodiol: (Moderate) Monitor for decreased efficacy of sildenafil if coadministration with taurursodiol is necessary as concurrent use may decrease sildenafil exposure.

What should I know about sildenafil before taking it?

Sotorasib: (Moderate) Monitor for decreased efficacy of sildenafil if coadministration with sotorasib is necessary as concurrent use may decrease sildenafil exposure. St. John's Wort, Hypericum perforatum: (Moderate) Monitor for decreased efficacy of sildenafil if coadministration with St. John's Wort is necessary as concurrent use may decrease sildenafil exposure. Sildenafil is a sensitive CYP3A substrate and St. Sildenafil has no direct relaxant effect on isolated human corpus cavernosum and, at recommended doses, has no effect in the absence of sexual stimulation.

As reported by the manufacturer, the pharmacodynamic response to sildenafil was assessed in eight double-blind, placebo-controlled crossover studies of patients with either organic or psychogenic erectile dysfunction.

In these studies sexual stimulation resulted in improved erections, as assessed by penile plethysmography, after sildenafil administration compared with placebo. Most studies evaluated the efficacy of sildenafil approximately 60 minutes post dose.

2.3 Dosage Adjustments in Specific Situations

John's Wort is a strong CYP3A inducer. Stiripentol: (Moderate) Consider a dose adjustment of sildenafil when coadministered with stiripentol. Coadministration may alter plasma concentrations of sildenafil resulting in an increased risk of adverse reactions and/or decreased efficacy. In vitro data predicts inhibition or induction of CYP3A4 by stiripentol potentially resulting in clinically significant interactions. Tacrolimus: (Moderate) Consider initiating sildenafil at a low dose (25 mg) in kidney transplant recipients receiving tacrolimus.

Does sildenafil interact with foods or drinks?

In a study of renal transplant patients, coadministration of tacrolimus with a single 50 mg dose of sildenafil resulted in an increase in the AUC, Cmax, and half-life of sildenafil. Decreases in blood pressure were also observed. No significant effect on the pharmacokinetic parameters of tacrolimus were observed. Tamsulosin: (Moderate) Due to the potential for symptomatic hypotension, patients should be stable on tamsulosin therapy before initiating therapy with the lowest dose of sildenafil. Tazemetostat: (Moderate) Monitor for decreased efficacy of sildenafil if coadministration with tazemetostat is necessary as concurrent use may decrease sildenafil exposure. The erectile response, as determined by penile plethysmography, generally increased with increasing sildenafil dose and plasma concentration.

The time course of effect was examined in one study.

8.6 Renal Impairment

When sildenafil is used for erectile dysfunction, consider a starting dose of 25 mg for patients receiving tucatinib. Vemurafenib: (Moderate) Concomitant use of vemurafenib with sildenafil may increase sildenafil exposure. Sildenafil is cleared predominantly by CYP3A (major route) and CYP2C9 (minor route). Use caution and monitor patients for potential sildenafil-related side effects. Verapamil: (Moderate) Monitor for an increase in sildenafil-related adverse reactions if coadministration with verapamil is necessary; consider a starting dose of 25 mg of sildenafil when prescribed for erectile dysfunction.

Revatio for Oral Suspension

PDE5 inhibitors, including sildenafil, may potentiate the hypotensive effects of vericiguat. Vigabatrin: (Major) Vigabatrin should not be used with phosphodiesterase inhibitors, which is associated with serious ophthalmic effects (e.g., retinopathy or glaucoma) unless the benefit of treatment clearly outweighs the risks. Vonoprazan; Amoxicillin; Clarithromycin: (Major) Coadministration of clarithromycin is not recommended in patients receiving sildenafil for pulmonary arterial hypertension (PAH). Voriconazole: (Major) Coadministration of voriconazole is not recommended in patients receiving sildenafil for pulmonary arterial hypertension (PAH). When sildenafil is used for erectile dysfunction, consider a starting dose of 25 mg for patients receiving voriconazole. The effects of sildenafil were evident for up to 4 hours, but the response was diminished compared to 2 hours.In vitro studies show that sildenafil is selective for PDE5 and its effect is more potent on PDE5 than on other known phosphodiesterases.

• Store sildenafil tablets in a cool, dry place away from moisture.
• Keep out of reach of children and pets.
• Expiry date can be checked on the packaging.

The approximately 4,000-fold selectivity for PDE5 versus PDE3 is important because PDE3 is involved in control of cardiac contractility.

Route of administration

Sildenafil is a sensitive CYP3A4 substrate and tazemetostat is a weak CYP3A4 inducer. Telmisartan; Amlodipine: (Moderate) Monitor for additive hypotension if amlodipine is administered concurrently with sildenafil, as both agents act independently to reduce blood pressure. Telotristat Ethyl: (Moderate) Monitor for decreased efficacy of sildenafil if coadministration with telotristat is necessary as concurrent use may decrease sildenafil exposure. Terazosin: (Moderate) Due to the potential for symptomatic hypotension, patients should be stable on alpha-blocker therapy before initiating therapy with the lowest dose of sildenafil. Tezacaftor; Ivacaftor: (Moderate) Increased monitoring is recommended if ivacaftor is administered concurrently with CYP2C9 substrates, such as sildenafil.

Does sildenafil interact with other medicines (drug interactions)?

Tipranavir: (Major) Sildenafil is contraindicated for use with tipranavir when used for pulmonary arterial hypertension (PAH). Sildenafil is a sensitive CYP3A4 substrate; tipranavir is a strong CYP3A4 inhibitor. Trandolapril; Verapamil: (Moderate) Monitor for an increase in sildenafil-related adverse reactions if coadministration with verapamil is necessary; pfizer sildenafil 100 consider a starting dose of 25 mg of sildenafil when prescribed for erectile dysfunction. Tranylcypromine: (Moderate) Additive hypotensive effects may be seen when monoamine oxidase inhibitors (MAOIs) are combined with sildenafil. Tucatinib: (Major) Coadministration with tucatinib is not recommended in patients receiving sildenafil for pulmonary arterial hypertension (PAH). Sildenafil can also inhibit PDE5 present in esophageal smooth muscle, lung tissue, and brain tissue.

4.1 Nitrates

Voxelotor: (Moderate) Monitor for an increase in sildenafil-related adverse reactions if coadministration with voxelotor is necessary; consider a starting dose of 25 mg of sildenafil when prescribed for erectile dysfunction. Zafirlukast: (Moderate) Concomitant use of zafirlukast with sildenafil may increase sildenafil exposure. In vitro studies suggest zafirlukast inhibits CYP3A (weak) and CYP2C9 (moderate top potent). LiQrev Oral Susp: 1mL, 10mgRevatio/Sildenafil/Sildenafil Citrate Intravenous Inj Sol: 0.8mg, 1mLRevatio/Sildenafil/Sildenafil Citrate Oral Pwd F/Recon: 1mL, 10mgRevatio/Sildenafil/Sildenafil Citrate/Viagra Oral Tab: 20mg, 25mg, 50mg, 100mg 100 mg/day PO for erectile dysfunction; 240 mg/day PO or 30 mg/day IV for pulmonary arterial hypertension. 100 mg/day PO for erectile dysfunction; 240 mg/day PO or 30 mg/day IV for pulmonary arterial hypertension.

Platelet-aggregation Inhibitors

Weight 45 kg or more: 40 mg PO 3 times daily.Weight 21 to 44 kg: 20 mg PO 3 times daily. Weight 45 kg or more: 40 mg PO 3 times daily.Weight 21 to 44 kg: 20 mg PO 3 times daily.Weight 20 kg or less: 10 mg PO 3 times daily. Guidelines recommend 1 mg/kg/dose PO every 8 hours. Guidelines recommend 1 mg/kg/dose PO every 8 hours and 0.4 mg/kg IV as a loading dose followed by a continuous infusion of 0.067 mg/kg/hour. Nitric oxide then activates the enzyme guanylate cyclase, which results in increased levels of cGMP. Inhibition of PDE5 in lung tissue results in relaxation of pulmonary vascular smooth muscle and subsequently pulmonary vasodilation, thereby making sildenafil an effective agent in treating pulmonary hypertension.

What other drugs will affect sildenafil?

Monitor for signs and symptoms of hypotension during transition of therapy. PDE5 inhibitors, including sildenafil, may potentiate the hypotensive effects of riociguat. Ritlecitinib: (Moderate) Monitor for an increase in sildenafil-related adverse reactions if coadministration with ritlecitinib is necessary; consider a starting dose of 25 mg of sildenafil when prescribed for erectile dysfunction. Ritonavir: (Major) Coadministration of ritonavir is contraindicated in patients receiving sildenafil for pulmonary arterial hypertension (PAH). Sapropterin: (Moderate) Sapropterin acts as a cofactor in the synthesis of nitric oxide and may cause vasorelaxation.

What’s the youngest age for which Viagra is safe to use?

Caution should be exercised when administering sapropterin in combination with drugs that affect nitric oxide-mediated vasorelaxation such as phosphodiesterase inhibitors. When given together these agents may produce an additive reduction in blood pressure. The combination of sapropterin and a phosphodiesterase (PDE5) inhibitor did not significantly reduce blood pressure when administered concomitantly in animal studies. The additive effect of these agents has not been studied in humans. Saquinavir: (Major) Sildenafil is contraindicated for use with saquinavir when used for pulmonary arterial hypertension (PAH).

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