Cialis drug interactions
Potential for Pharmacodynamic Interactions with Cialis
Cialis and Nitrates — Administration of Cialis to patients who are using any form of organic nitrate, is contraindicated. In clinical pharmacology studies, Cialis was shown to potentiate the hypotensive effect of nitrates. In a patient who has taken Cialis, where nitrate administration is deemed medically necessary in a life-threatening situation, at least 48 hours should elapse after the last dose of Cialis before nitrate administration is considered. In such circumstances, nitrates should still only be administered under close medical supervision with appropriate hemodynamic monitoring.
Cialis andAlpha Blockers — Caution is advised when PDE5 inhibitors are coadministered with alpha blockers. PDE5 inhibitors, including Cialis, and alpha-adrenergic blocking agents are both vasodilators with blood-pressure-lowering effects. When vasodilators are used in combination, an additive effect on blood pressure may be anticipated. Clinical pharmacology studies have been conducted with coadministration of Cialis with doxazosin or tamsulosin.
Cialis and Antihypertensives — PDE5 inhibitors, including Cialis, are mild systemic vasodilators. Clinical pharmacology studies were conducted to assess the effect of Cialis on the potentiation of the blood-pressure-lowering effects of selected antihypertensive medications (amlodipine, angiotensin II receptor blockers, bendrofluazide, enalapril, and metoprolol). Small reductions in blood pressure occurred following coadministration of Cialis with these agents compared with placebo.
Cialis and Alcohol — Both alcohol and Cialis, a PDE5 inhibitor, act as mild vasodilators. When mild vasodilators are taken in combination, blood-pressure-lowering effects of each individual compound may be increased. Substantial consumption of alcohol (e.g., 5 units or greater) in combination with Cialis can increase the potential for orthostatic signs and symptoms, including increase in heart rate, decrease in standing blood pressure, dizziness, and headache. Cialis did not affect alcohol plasma concentrations and alcohol did not affect Cialis plasma concentrations.
Potential for Other Drugs to Affect Cialis
Cialis and Antacids — Simultaneous administration of an antacid (magnesium hydroxide/aluminum hydroxide) and Cialis reduced the apparent rate of absorption of Cialis without altering exposure (AUC) to Cialis.
Cialis and H2Antagonists (e.g. Nizatidine) — An increase in gastric pH resulting from administration of nizatidine had no significant effect on pharmacokinetics.
Cialis and Cytochrome P450 Inhibitors — Cialis is a substrate of and predominantly metabolized by CYP3A4. Studies have shown that drugs that inhibit CYP3A4 can increase Cialis exposure.
Cialis and CYP3A4 (e.g., Ketoconazole) — Ketoconazole (400 mg daily), a selective and potent inhibitor of CYP3A4, increased Cialis 20 mg single-dose exposure (AUC) by 312% and Cmax by 22%, relative to the values for Cialis 20 mg alone. Ketoconazole (200 mg daily) increased Cialis 10-mg single-dose exposure (AUC) by 107% and Cmax by 15%, relative to the values for Cialis 10 mg alone.
Although specific interactions have not been studied, other CYP3A4 inhibitors, such as erythromycin, itraconazole, and grapefruit juice, would likely increase Cialis exposure.
Cialis and HIV Protease inhibitor — Ritonavir (500 mg or 600 mg twice daily at steady state), an inhibitor of CYP3A4, CYP2C9, CYP2C19, and CYP2D6, increased Cialis 20-mg single-dose exposure (AUC) by 32% with a 30% reduction in Cmax, relative to the values for Cialis 20 mg alone. Ritonavir (200 mg twice daily), increased Cialis 20-mg single-dose exposure (AUC) by 124% with no change in Cmax, relative to the values for Cialis 20 mg alone. Although specific interactions have not been studied, other HIV protease inhibitors would likely increase Cialis exposure.
Cialis and Cytochrome P450 Inducers — Studies have shown that drugs that induce CYP3A4 can decrease Cialis exposure.
Cialis and CYP3A4 (e.g., Rifampin) — Rifampin (600 mg daily), a CYP3A4 inducer, reduced Cialis 10-mg single-dose exposure (AUC) by 88% and Cmax by 46%, relative to the values for Cialis 10 mg alone. Although specific interactions have not been studied, other CYP3A4 inducers, such as carbamazepine, phenytoin, and phenobarbital, would likely decrease Cialis exposure. No dose adjustment is warranted. The reduced exposure of Cialis with the coadministration of rifampin or other CYP3A4 inducers can be anticipated to decrease the efficacy of Cialis for once daily use; the magnitude of decreased efficacy is unknown.
Potential for Cialis to Affect Other Drugs
Cialis and Aspirin — Cialis did not potentiate the increase in bleeding time caused by aspirin.
Cialis and Cytochrome P450 Substrates — Cialis is not expected to cause clinically significant inhibition or induction of the clearance of drugs metabolized by cytochrome P450 (CYP) isoforms. Studies have shown that Cialis does not inhibit or induce P450 isoforms CYP1A2, CYP3A4, CYP2C9, CYP2C19, CYP2D6, and CYP2E1.
Cialis and CYP1A2 (e.g. Theophylline) — Cialis had no significant effect on the pharmacokinetics of theophylline. When Cialis was administered to subjects taking theophylline, a small augmentation (3 beats per minute) of the increase in heart rate associated with theophylline was observed.
Cialis and CYP2C9 (e.g. Warfarin) — Cialis had no significant effect on exposure (AUC) to S-warfarin or R-warfarin, nor did Cialis affect changes in prothrombin time induced by warfarin.
Cialis and CYP3A4 (e.g. Midazolam or Lovastatin) — Cialis had no significant effect on exposure (AUC) to midazolam or lovastatin.
Cialis and P-glycoprotein (e.g. Digoxin) — Coadministration of Cialis (40 mg once per day) for 10 days did not have a significant effect on the steady-state pharmacokinetics of digoxin (0.25 mg/day) in healthy subjects.
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