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STAXYN (VARDENAFIL): DRUG INTERACTIONS

The drug interaction studies described below were conducted using vardenafil film-coated tablets.

Potential for Pharmacodynamic Interactions with Staxyn (Vardenafil Hydrochloride)

Nitrates

Concomitant use of Staxyn and nitrates is contraindicated. The blood pressure lowering effects of sublingual nitrates (0.4 mg) taken 1 and 4 hours after vardenafil and increases in heart rate when taken at 1, 4 and 8 hours after vardenafil were potentiated by a 20 mg dose of vardenafil in healthy middle-aged subjects. These effects were not observed when vardenafil 20 mg was taken 24 hours before the nitroglycerin (NTG). Potentiation of the hypotensive effects of nitrates for patients with ischemic heart disease has not been evaluated, and concomitant use of Vardenafil HCl (Staxyn) and nitrates is contraindicated.

Alpha-Blockers

Patients taking alpha-blockers should not initiate vardenafil therapy with Staxyn. Patients treated with alpha-blockers who have previously used vardenafil film-coated tablets may be switched to Vardenafil HCl (Staxyn) tablets at the advice of their healthcare provider. Caution is advised when PDE5 inhibitors are co-administered with alpha-blockers. PDE5 inhibitors, including Staxyn 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 co-administration of vardenafil with terazosin or tamsulosin.

Antihypertensives

Staxyn (Vardenafil) may add to the blood pressure lowering effect of antihypertensive agents. In a clinical pharmacology study of patients with erectile dysfunction, single doses of 20 mg vardenafil caused a mean maximum decrease in supine blood pressure of 7 mmHg systolic and 8 mmHg diastolic (compared to placebo), accompanied by a mean maximum increase of heart rate of 4 beats per minute. The maximum decrease in blood pressure occurred between 1 and 4 hours after dosing. Following multiple dosing for 31 days, similar blood pressure responses were observed on Day 31 as on Day 1.

Alcohol

Vardenafil 20 mg did not potentiate the hypotensive effects of alcohol during the 4-hour observation period in healthy volunteers when administered with alcohol (0.5 g/kg body weight: approximately 40 mL of absolute alcohol in a 70 kg person). Alcohol and vardenafil plasma levels were not altered when dosed simultaneously.

Effect of Other Drugs on Vardenafil

In vitro studies

Studies in human liver microsomes showed that Staxyn (Vardenafil) tablets is metabolized primarily by cytochrome P450 (CYP) isoforms 3A4/5, and to a lesser degree by CYP2C9. Therefore, inhibitors of these enzymes are expected to reduce vardenafil clearance.

In vivo studies

Do not use Staxyn with moderate and potent CYP3A4 inhibitors such as clarithromycin, erythromycin, grapefruit juice, itraconazole, ketoconazole, indinavir, saquinavir, atazanavir, ritonavir as the systemic concentration of vardenafil is increased in their presence.

Potent CYP3A4 inhibitors

Ketoconazole (200 mg once daily) produced a 10-fold increase in vardenafil area under the curve (AUC) and a 4-fold increase in maximum concentration (Cmax) when co-administered with vardenafil 5 mg in healthy volunteers.

Indinavir (800 mg t.i.d.) co-administered with vardenafil 10 mg resulted in a 16-fold increase in vardenafil AUC, a 7-fold increase in vardenafil Cmax and a 2-fold increase in vardenafil half-life.

Ritonavir (600 mg b.i.d.) co-administered with vardenafil 5 mg resulted in a 49-fold increase in vardenafil AUC and a 13-fold increase in vardenafil Cmax. The interaction is a consequence of blocking hepatic metabolism of vardenafil by ritonavir, a highly potent CYP3A4 inhibitor, which also inhibits CYP2C9.

Moderate CYP3A4 inhibitors

Erythromycin (500 mg t.i.d.) produced a 4-fold increase in vardenafil AUC and a 3-fold increase in vardenafil Cmax when co-administered with vardenafil 5 mg in healthy volunteers.

Other Drug Interactions

No pharmacokinetic interactions were observed between vardenafil and the following drugs: warfarin, glyburide, digoxin, an antacid based on magnesium-aluminum hydroxide, and ranitidine. In the warfarin study, vardenafil had no effect on the prothrombin time or other pharmacodynamic parameters.

Cimetidine (400 mg b.i.d.) had no effect on AUC and Cmax of vardenafil when co-administered with 20 mg vardenafil in healthy volunteers.

Effects of Vardenafil on Other Drugs

In vitro studies

Vardenafil Hydrochloride (Staxyn) and its metabolites had no effect on CYP1A2, 2A6, and 2E1 (Ki >100 micromolar). Weak inhibitory effects toward other isoforms (CYP2C8, 2C9, 2C19, 2D6, 3A4) were found, but Ki values were in excess of plasma concentrations achieved following dosing. The most potent inhibitory activity was observed for vardenafil metabolite M1, which had a Ki of 1.4 micromolar toward CYP3A4, which is about 20 times higher than the M1 Cmax values after an 80 mg vardenafil dose.

In vivo studies

Nifedipine

Vardenafil 20 mg, when co-administered with slow-release nifedipine 30 mg or 60 mg once daily, did not affect the relative AUC or Cmax of nifedipine, a drug that is metabolized via CYP3A4. Nifedipine did not alter the plasma levels of vardenafil when taken in combination. In these patients whose hypertension was controlled with nifedipine, vardenafil 20 mg produced mean additional supine systolic/diastolic blood pressure reductions of 6/5 mmHg compared to placebo.

Ritonavir and Indinavir

Upon concomitant administration of 5 mg vardenafil with 600 mg b.i.d. ritonavir, the Cmax and AUC of ritonavir were reduced by approximately 20%. Upon administration of 10 mg of vardenafil (film-coated tablets) with 800 mg t.i.d. indinavir, the Cmax and AUC of indinavir were reduced by 40% and 30%, respectively.

Aspirin

Vardenafil Hydrochloride (Staxyn) tablets 10 mg and 20 mg did not potentiate the increase in bleeding time caused by aspirin (two 81 mg tablets).

Other Interactions

Vardenafil had no effect on the pharmacodynamics of glyburide (glucose and insulin concentrations) and warfarin (prothrombin time or other pharmacodynamic parameters).

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