A 67 y/o male patient presents to your clinic for his annual check-up and refills on his prescriptions. As the appointment comes to an end, he mentioned he's having 'some trouble in the bedroom.' He'd like a prescription of Viagra to try out.

He's generally healthy except for very mild hypercholesterolemia and benign prostatic hyperplasia. His vital signs are normal and his labs are within normal limits except for slightly elevated cholesterol, controlled with lifestyle changes and diet. His only medication is terazosin 5mg po QHS for BPH.

Do you write the prescription for Viagra®? Why or why not?

No. Alpha blockers (ex terazosin, prazosin, doxazosin) are CONTRAindicated for use with PDE5 inhibitors, specifically vardenafil [Levitra®], and tadalafil [Cialis®]. The combination can cause clinically significant decreases in blood pressure. The combination of sildenafil [Viagra®] and tamsulosin [Flomax®] is not contraindicated but the package insert lists the combination as a "precaution". Hypotension may occur with this combination as well. I found no data on the combination on alfuzosin [Uroxatral®] and the PDE5 inhibitors different than that listed above.

A. ALPHA-1 ADRENERGIC BLOCKERS (with sildenafil - Viagra®)

        1. Summary: Symptomatic postural hypotension has occurred in patients receiving simultaneous doses of doxazosin 4 milligrams (mg) and sildenafil 25 mg. Mean reductions of supine systolic and diastolic blood pressure have been observed in patients treated concurrently with doxazosin and sildenafil (Prod Info Viagra(R), 2002).

        2. Adverse Effect: potentiation of hypotensive effects

        3. Clinical Management: If co-administration is required, sildenafil should not be given in doses exceeding 25 milligrams within 4 hours of receiving an alpha-1 adrenergic blocker.

        4. Severity: moderate

        5. Onset: rapid

        6. Documentation: fair

        7. Probable Mechanism: unknown

B. ALPHA-1 ADRENERGIC BLOCKERS (with vardenafil - Levitra®)

        1. Summary: Significant hypotension developed in a substantial number of subjects when vardenafil 10 or 20 mg was given to healthy volunteers either simultaneously or 6 hours after a single dose of terazosin 10 mg. When vardenafil 10 mg and terazosin 10 mg were simultaneously administered, 6 of 8 subjects experienced a standing systolic blood pressure of less than 85 mm Hg. When vardenafil 20 mg and terazosin 10 mg were simultaneously administered, 2 of 9 subjects experienced a standing systolic blood pressure of less than 85 mm Hg. Seven of 28 subjects who received vardenafil 20 mg experienced a decrease in standing systolic blood pressure below 85 mm Hg when vardenafil dosing was separated from terazosin 10 mg by 6 hours. In a similar study involving tamsulosin, 1 of 24 subjects receiving vardenafil 20 mg and tamsulosin 0.4 mg separated by 6 hours experienced a standing systolic blood pressure below 85 mm Hg. The administration of lower doses of vardenafil with alpha blockers has not been completely evaluated to determine if they can be safely administered together. Based on these data, vardenafil should not be used in patients on alpha-1 adrenergic blocker therapy (Sweetman, 2004; Prod Info Levitra(R), 2003; Prod Info Hytrin(R), 2002; Prod Info Minipress(R), 2000; Prod Info Dibenzyline(R), 2000; Prod Info Phentolamine mesylate for injection, 1999; Jardin et al, 1993; Yoshioka et al, 1990; van Zwieten et al, 1990; Rosenthal, 1987; Taylor et al, 1983).

        2. Adverse Effect: potentiation of hypotensive effects

        3. Clinical Management: Because the coadministration of alpha-1 adrenergic blockers and vardenafil can produce hypotension, vardenafil is contraindicated in patients taking alpha-1 adrenergic blockers.

        4. Severity: major

        5. Onset: rapid

        6. Documentation: fair

C. ALPHA-1 ADRENERGIC BLOCKERS (with tadalafil - Cialis®)

        1. Summary: Administration of tadalafil to patients taking alpha-adrenergic antagonists other than tamsulosin 0.4 mg once daily is contraindicated. In a drug-drug interaction study, healthy subjects taking tadalafil 20 mg in addition to doxazosin 8 mg daily, significant augmentation of the blood-pressure-lowering effect of doxazosin occurred. No significant decreases in blood pressure were observed when tadalafil 20 mg was administered to healthy subjects taking tamsulosin 0.4 mg once daily (Prod Info Cialis(R), 2003).

        2. Adverse Effect: potentiation of hypotensive effects

        3. Clinical Management: Because the coadministration of alpha-1 adrenergic blockers and tadalafil can produce hypotension, tadalafil is contraindicated in patients taking alpha-1 adrenergic blockers.

        4. Severity: major

        5. Onset: rapid

        6. Documentation: fair

        7. Probable Mechanism: unknown