Sildenafil interactions
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Sildenafil Interactions: A Comprehensive Overview
Introduction to Sildenafil and Its Mechanism of Action
Sildenafil, a selective inhibitor of cyclic guanosine monophosphate (cGMP)-specific phosphodiesterase type 5 (PDE5), is widely used for the treatment of erectile dysfunction (ED) and pulmonary arterial hypertension (PAH) 27. Its mechanism involves the enhancement of the nitric oxide (NO)-cGMP pathway, leading to smooth muscle relaxation and increased blood flow .
Sildenafil and Blood Pressure Medications
Interaction with Organic Nitrates
Sildenafil significantly potentiates the hypotensive effects of organic nitrates, such as glyceryl trinitrate. Studies have shown that coadministration of sildenafil with glyceryl trinitrate leads to a substantial decrease in blood pressure, making this combination contraindicated due to the risk of severe hypotension .
Interaction with Calcium Channel Blockers
In patients taking the calcium antagonist amlodipine, sildenafil has been shown to produce additive reductions in blood pressure. However, these effects are not synergistic and are comparable to the blood pressure reductions observed in healthy men taking sildenafil alone .
Sildenafil and Endothelin Receptor Antagonists
Macitentan
The pharmacokinetics of macitentan, an endothelin receptor antagonist, are not significantly affected by sildenafil. However, sildenafil's plasma concentrations are increased when coadministered with macitentan, suggesting a minor pharmacokinetic interaction that does not necessitate dose adjustments .
Bosentan
Bosentan, another endothelin receptor antagonist, decreases the plasma concentration of sildenafil significantly. Conversely, sildenafil increases the plasma concentration of bosentan. This mutual pharmacokinetic interaction suggests that dosage adjustments may be necessary when these drugs are used in combination .
Sildenafil and Antiepileptic Drugs
Sildenafil has been reported to enhance the anticonvulsant action of several antiepileptic drugs (AEDs) in animal models. This interaction appears to be both pharmacodynamic and pharmacokinetic, particularly with drugs like levetiracetam and valproic acid .
Sildenafil and CYP3A Inhibitors
Fluconazole
Fluconazole, a CYP3A inhibitor, significantly increases the plasma concentration of sildenafil in infants, necessitating a dose reduction of sildenafil by approximately 60% to avoid potential toxicity .
Clarithromycin and Itraconazole
Both clarithromycin and itraconazole, moderate CYP3A inhibitors, double the systemic exposure of sildenafil. This interaction underscores the importance of monitoring and potentially adjusting sildenafil doses when coadministered with these inhibitors .
Sildenafil and Antipsychotic-Induced Erectile Dysfunction
Sildenafil has been shown to be effective and well-tolerated in treating erectile dysfunction induced by antipsychotic medications. Patients reported significant improvements in erectile function without major side effects or adverse drug interactions .
Visual Side Effects of Sildenafil
High doses of sildenafil can cause transient and reversible visual side effects, including changes in color vision, blurred vision, and photophobia. These effects are generally mild and do not result in permanent damage to the visual system when taken as prescribed .
Conclusion
Sildenafil interacts with a variety of medications, including blood pressure drugs, endothelin receptor antagonists, antiepileptic drugs, and CYP3A inhibitors. These interactions can significantly alter the pharmacokinetics and pharmacodynamics of sildenafil, necessitating careful monitoring and potential dose adjustments. Despite these interactions, sildenafil remains a highly effective treatment for erectile dysfunction and pulmonary arterial hypertension when used appropriately.
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