Drug interactions between isradipine and Levitra

MONITOR: Phosphodiesterase-5 (PDE5) inhibitors such as sildenafil and vardenafil may potentiate the hypotensive effect of calcium channel blockers. These agents inhibit PDE5-mediated degradation of cyclic guanosine monophosphate (cGMP), which in vascular smooth muscles can cause peripheral vasodilation that may be additive with that induced by calcium channel blockers. In addition, most calcium channel blockers are inhibitors and/or substrates of CYP450 3A4 and may increase the plasma levels of sildenafil and vardenafil by inhibiting their metabolism via the isoenzyme. In hypertensive patients, coadministration of sildenafil (100 mg) and amlodipine (5 mg or 10 mg) resulted in mean additional reductions of supine blood pressure of 8 mmHg systolic and 7 mmHg diastolic. Similarly, coadministration of vardenafil (20 mg) and nifedipine (slow-release 30 mg or 60 mg once daily) resulted in mean additional reductions of supine blood pressure of 6 mmHg systolic and 5 mmHg diastolic compared to placebo. However, no significant alterations in the pharmacokinetics of nifedipine or vardenafil were observed.

MANAGEMENT: Caution is advised if PDE5 inhibitors are prescribed to patients treated with calcium channel blockers. Patients receiving the combination should be advised to avoid rising abruptly from a sitting or recumbent position and to contact their physician if they experience symptoms of hypotension such as dizziness, lightheadedness, or fainting. In addition, patients should promptly notify their physician if they experience excessive adverse effects of PDE5 inhibitors such as pain or tightness in the chest or jaw, irregular heartbeat, nausea, shortness of breath, visual disturbances, syncope, or prolonged erection (greater than 4 hours).