Drug Interactions between OraVerse and sildenafil

Consumer information for this interaction is not currently available.

MONITOR: Concurrent use of a phosphodiesterase-5 (PDE5) inhibitor with phentolamine may result in additive adverse effects resulting from both medications acting as vasodilators. Additional factors may affect the severity of this interaction including the route of administration, dosing regimen, amount of each medication absorbed systemically, presence of intravascular depletion, and use of other medications with hypotensive effects. Reductions of systolic BP ranging from 2.5 mmHg to greater than 30 mmHg from baseline have been reported with alfuzosin, doxazosin, tamsulosin and/or terazosin. However, data are not available for all formulations of phentolamine. There are studies which evaluate the combination of intracavernosal injections (ICIs) containing phentolamine with an oral PDE5 inhibitor for erectile dysfunction (ED). In one case series, 93 patients were treated for ED with sildenafil monotherapy or sildenafil in combination with ICI triple-therapy after failing a trial of ICI (monotherapy or triple therapy). Those who received sildenafil in combination with ICI triple-therapy (n=41) reported an increase in adverse effects (e.g., dizziness, syncope) when compared to monotherapy (49% with combination therapy vs. 31% with ICI alone and 37% with sildenafil alone).

MANAGEMENT: Caution and clinical monitoring for adverse effects (e.g., hypotension, dizziness, syncope, priapism) are advised if phentolamine is used in combination with a PDE5 inhibitor. Some manufacturers (both of PDE5 inhibitors as well as of phentolamine) advise against combining treatments for ED due to a lack of safety and efficacy data. However, there are guidelines specific to the treatment of ED which contain guidance for using an oral PDE5 inhibitor with ICIs containing phentolamine (though this may be an off-label indication for phentolamine). The severity of this interaction may be affected by additional factors listed above. In general, most product labeling recommends stabilizing a patient on either alpha-blocker therapy or PDE5 inhibitor therapy first and then initiating the other medication with the knowledge that increases in dosage may result in further lowering of blood pressure. If combination therapy is used, consultation with product labeling and relevant treatment guidelines as well as counseling the patient on potential adverse effects is recommended.