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.

Sources and full results

Most relevant research papers on this topic

Investigation of mutual pharmacokinetic interactions between macitentan, a novel endothelin receptor antagonist, and sildenafil in healthy subjects.

A minor pharmacokinetic interaction was observed between macitentan and sildenafil, but no dose adjustment is necessary during concomitant treatment with these medications.

RCTRigorous Journal

2014·

27citations

·P. Sidharta et al.

Sildenafil citrate and blood-pressure-lowering drugs: results of drug interaction studies with an organic nitrate and a calcium antagonist.

Sildenafil citrate can potentiate the hypotensive effects of glyceryl trinitrate, an organic nitrate, without significantly affecting heart rate or heart rate variability.

RCTHighly Cited

1999·

324citations

·David J. Webb et al.

Intravenous sildenafil and inhaled nitric oxide: a randomised trial in infants after cardiac surgery

Intravenous sildenafil enhanced the pulmonary vasodilator effects of inhaled nitric oxide in infants early after cardiac surgery, but also produced systemic hypotension and impaired oxygenation, which were not improved by iNO.

RCTHighly Cited

2003·

180citations

·C. Stocker et al.

Mutual pharmacokinetic interactions between steady-state bosentan and sildenafil

In healthy volunteers, bosentan and sildenafil have a mutual pharmacokinetic interaction, potentially influencing the dosage of each drug in combination treatments.

RCTVery Rigorous JournalHighly Cited

2007·

170citations

·G. Burgess et al.

Effect of sildenafil, a selective phosphodiesterase 5 inhibitor, on the anticonvulsant action of some antiepileptic drugs in the mouse 6-Hz psychomotor seizure model

Sildenafil increases the threshold for 6-Hz-induced psychomotor seizures in mice and enhances the anticonvulsant action of various antiepileptic drugs, without significantly affecting motor coordination, muscular strength, or long-term memory.

Non-RCTAnimal Study

2013·

23citations

·D. Nieoczym et al.

Physiologically-Based Pharmacokinetic Modeling Characterizes the CYP3A-Mediated Drug-Drug Interaction Between Fluconazole and Sildenafil in Infants

PBPK modeling can effectively predict drug-drug interactions in infants, with the need to include CYP3A7 parameters for accurate predictions.

Rigorous Journal

2020·

27citations

·Sara N Salerno et al.

Sildenafil citrate: a therapeutic update.

Sildenafil is an effective first-line therapy for erectile dysfunction in men, but its use should consider cost, risk, and patient access.

Systematic ReviewHighly Cited

2001·

95citations

·E. Boyce et al.

The utility of CYP3A activity endogenous markers for evaluating drug-drug interaction between sildenafil and CYP3A inhibitors in healthy subjects.

Sildenafil has moderate pharmacokinetic interaction with clarithromycin and itraconazole, and endogenous markers can effectively reflect CYP3A inhibition in drug-drug interactions.

RCT

2020·

10citations

·Soyoung Lee et al.

Sildenafil in the treatment of antipsychotic-induced erectile dysfunction: a randomized, double-blind, placebo-controlled, flexible-dose, two-way crossover trial.

Sildenafil citrate is a safe and effective treatment for antipsychotic-induced erectile dysfunction, with no major side effects or adverse drug interactions.

RCTHighly Cited

2006·

72citations

·R. Gopalakrishnan et al.

Visual Side Effects Linked to Sildenafil Consumption: An Update

Sildenafil may cause transient and reversible visual side effects, but does not cause permanent toxic effects on chorioretinal tissue and photoreceptors when taken under physician guidance.

Systematic ReviewRigorous Journal

2021·

19citations

·Eva Ausó et al.

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