Critical Drug Interactions with Sildenafil
Life-Threatening Interactions: Nitrates
The most serious interaction occurs between sildenafil and nitrate medications. This combination can cause a dangerous drop in blood pressure that may be life-threatening. Nitrates include glyceryl trinitrate (GTN) spray, isosorbide mononitrate, and isosorbide dinitrate commonly prescribed for chest pain or heart conditions. Patients taking any form of nitrates should not use sildenafil under any circumstances.
Blood Pressure Medications
Sildenafil can enhance the blood pressure-lowering effects of antihypertensive medications. This includes ACE inhibitors, calcium channel blockers, and diuretics. Whilst not always contraindicated, your prescriber may need to adjust dosages or monitor you more closely. The combination may cause dizziness, fainting, or excessive blood pressure reduction, particularly when standing up quickly.
Alpha-Blocker Interactions
Alpha-blockers such as doxazosin, tamsulosin, and alfuzosin are commonly prescribed for enlarged prostate or high blood pressure. When combined with sildenafil, these medications can cause symptomatic hypotension. If both medications are necessary, your doctor may recommend starting with the lowest sildenafil dose and ensuring your alpha-blocker dose is stable before beginning ED treatment.
CYP3A4 Enzyme Interactions
Sildenafil is metabolised by the CYP3A4 enzyme system. Medications that inhibit this enzyme can increase sildenafil levels in your body, potentially causing stronger effects or side effects. These include certain antibiotics like erythromycin and clarithromycin, antifungal medications such as ketoconazole and itraconazole, and HIV protease inhibitors. Your prescriber may need to reduce the sildenafil dose if you're taking these medications.
Other Considerations
Riociguat, used for pulmonary hypertension, is contraindicated with sildenafil. Certain recreational substances can also interact dangerously with ED medications. Always inform your prescriber about all medications, supplements, and substances you're using. Both branded Viagra and generic sildenafil have identical interaction profiles, so the choice between options at EverydayMeds doesn't affect safety considerations.
Food and Alcohol Interactions
Whilst not drug interactions, food and alcohol can affect sildenafil's effectiveness. High-fat meals may delay the medication's onset, whilst excessive alcohol can impair erectile function and increase the risk of side effects like dizziness or low blood pressure.
