POWERGRA 100

Indications

• Erectile dysfunction
• Pulmonary arterial hypertension

Dosage

Children: Sildenafil is not typically indicated for use in the paediatric population. Refer to the BNF for Children for any specific guidance.

Adults: Refer to the BNF for specific dosage recommendations based on the condition being treated, taking into account individual patient factors.

Mechanism of action

Sildenafil works by inhibiting the enzyme phosphodiesterase type 5 (PDE5), which is responsible for the degradation of cyclic guanosine monophosphate (cGMP). Increased levels of cGMP lead to relaxation of vascular smooth muscle, allowing for enhanced blood flow to specific areas, particularly the penis and lungs. This mechanism is contingent on sexual stimulation for its effects on erectile function.

Pharmacodynamics

The pharmacodynamics of sildenafil involves its ability to selectively inhibit PDE5, leading to increased concentrations of cGMP. This results in vasodilation and increased blood flow, which is clinically observed as improved erectile function in men and reduced pulmonary vascular resistance in patients with pulmonary arterial hypertension. The onset of action is generally within 30 to 60 minutes, with a peak effect around 1 hour post-administration.

Pharmacokinetics

Sildenafil is rapidly absorbed following oral administration, with a bioavailability of approximately 40%. Peak plasma concentrations are typically reached within 30 to 120 minutes, depending on food intake. The drug is primarily metabolized by the liver via cytochrome P450 enzymes, particularly CYP3A4 and CYP2C9, producing active metabolites. The elimination half-life of sildenafil is about 4 hours, and it is primarily excreted through feces and urine.

Contra-indications

• Severe cardiovascular disorders
• Recent history of stroke or myocardial infarction
• Concurrent use of nitrates or nitric oxide donors
• Known hypersensitivity to sildenafil or any of its components

Adverse effects

• Headache
• Flushing
• Dyspepsia
• Nasal congestion
• Visual disturbances, including blue tint to vision
• Priapism
• Hypotension

Interactions

• Nitrates - may cause severe hypotension
• Alpha-blockers - can lead to symptomatic hypotension
• CYP3A4 inhibitors (e.g., ketoconazole, erythromycin) - may increase sildenafil levels
• CYP3A4 inducers (e.g., rifampicin, carbamazepine) - may decrease sildenafil levels

Precautions

• Use with caution in patients with cardiovascular risk factors
• Monitor for potential drug interactions, especially with antihypertensives
• Consider potential effects on vision and hearing

Pregnancy

There are no adequate and well-controlled studies in pregnant women. Sildenafil should not be used during pregnancy unless clearly needed.

Breast-feeding

It is not known whether sildenafil is excreted in human milk. Caution is advised when administering to breastfeeding women.

Storage

Store at room temperature, away from light and moisture. Keep out of reach of children.

Formulations

• Tablets (25 mg, 50 mg, 100 mg)
• Oral suspension