Erythromycin: Major Avoid coadministration of erythromycin genital tadalafil for the treatment of pulmonary. Tadalafil is metabolized predominantly by the hepatic cytochrome P 3A4 isoenzyme. Inhibitors of CYP3A4, such as ketoconazole, may reduce tadalafil clearance. Potent inhibitors of CYP3A4, such as erythromycin, may reduce tadalafil clearance. Erythromycin; Sulfisoxazole: Major Avoid coadministration of erythromycin and tadalafil for the treatment of pulmonary hypertension. Ethanol: Moderate Patients should limit the intake of alcohol while taking tadalafil, and not ingest alcohol to excess.