Effects on Blood Pressure When Administered with Nitrates
In clinical pharmacology studies, tadalafil (5 to 20 mg) was shown to potentiate the hypotensive effect of nitrates.
Do not use tadalafil tablets in patients taking any form of nitrates [see Contraindications (4.1)]. A double–blind, placebo–controlled, crossover study in 150 male subjects at least 40 years of age (including subjects with diabetes mellitus and/or controlled hypertension) assessed the interaction between nitroglycerin and tadalafil. Subjects received daily doses of tadalafil 20 mg or matching placebo for 7 days and then were given a single dose of 0.4 mg sublingual nitroglycerin (NTG) at pre–specified timepoints following their last dose of tadalafil (2, 4, 8, 24, 48, 72, and 96 hours after tadalafil). A significant interaction between tadalafil and NTG was observed at each timepoint up to and including 24 hours. At 48 hours, by most hemodynamic measures, the interaction between tadalafil and NTG was not observed, although a few more tadalafil subjects compared to placebo experienced greater blood–pressure lowering effects at this timepoint. After 48 hours, the interaction was not detectable. [See Contraindications (4.1) and Warnings and Precautions (5.1)].
Effects on Blood Pressure
Tadalafil 20 mg administered to healthy male subjects produced no significant difference compared to placebo in supine systolic and diastolic blood pressure (difference in the mean maximal decrease of 1.6/0.8 mm Hg, respectively) and in standing systolic and diastolic blood pressure (difference in the mean maximal decrease of 0.2/4.6 mm Hg, respectively). In addition, there was no significant effect on heart rate.
Effects on Blood Pressure When Administered with Antihypertensives
Amlodipine — A study assessed the interaction between amlodipine (5 mg daily) and tadalafil 10 mg. There was no effect of tadalafil on amlodipine blood levels and no effect of amlodipine on tadalafil blood levels. The mean reduction in supine systolic/diastolic blood pressure because of tadalafil 10 mg in subjects taking amlodipine was 3/2 mm Hg, compared to placebo. In a similar study using tadalafil 20 mg, there were no clinically significant differences between tadalafil and placebo in subjects taking amlodipine.
Angiotensin II receptor blockers (with and without other antihypertensives) — A study assessed the interaction between angiotensin II receptor blockers and tadalafil 20 mg. Subjects in the study were taking any marketed angiotensin II receptor blocker, either alone, as a component of a combination product, or as part of a multiple antihypertensive regimen. Following dosing, ambulatory measurements of blood pressure revealed differences between tadalafil and placebo of 8/4 mm Hg in systolic/diastolic blood pressure.
Bendroflumethiazide — A study assessed the interaction between bendroflumethiazide (2.5 mg daily) and tadalafil 10 mg. Following dosing, the mean reduction in supine systolic/diastolic blood pressure because of tadalafil 10 mg in subjects taking bendroflumethiazide was 6/4 mm Hg, compared to placebo.
Enalapril — A study assessed the interaction between enalapril (10 to 20 mg daily) and tadalafil 10 mg. Following dosing, the mean reduction in supine systolic/diastolic blood pressure because of tadalafil 10 mg in subjects taking enalapril was 4/1 mm Hg, compared to placebo.
Metoprolol — A study assessed the interaction between sustained–release metoprolol (25 to 200 mg daily) and tadalafil 10 mg. Following dosing, the mean reduction in supine systolic/diastolic blood pressure because of tadalafil 10 mg in subjects taking metoprolol was 5/3 mm Hg, compared to placebo.
Effects on Blood Pressure When Administered with Alcohol
Alcohol and PDE5 inhibitors, including tadalafil, are mild systemic vasodilators. The interaction of tadalafil with alcohol was evaluated in three clinical pharmacology studies. In two of these, alcohol was administered at a dose of 0.7 g/kg, which is equivalent to approximately 6 ounces of 80–proof vodka in an 80–kg male, and tadalafil was administered at a dose of 10 mg in one study and 20 mg in another. In both these studies, all patients imbibed the entire alcohol dose within 10 minutes of starting. In one of these two studies, blood alcohol levels of 0.08% were confirmed. In these two studies, more patients had clinically significant decreases in blood pressure on the combination of tadalafil and alcohol as compared to alcohol alone. Some subjects reported postural dizziness, and orthostatic hypotension was observed in some subjects. When tadalafil 20 mg was administered with a lower dose of alcohol (0.6 g/kg, which is equivalent to approximately 4 ounces of 80–proof vodka, administered in less than 10 minutes), orthostatic hypotension was not observed, dizziness occurred with similar frequency to alcohol alone, and the hypotensive effects of alcohol were not potentiated.
Tadalafil did not affect alcohol plasma concentrations and alcohol did not affect tadalafil plasma concentrations.
Effects on Blood Pressure When Administered with Alpha-Blockers
Alpha-blockers and PDE5 inhibitors, including tadalafil, are systemic vasodilators. In subjects receiving concomitant tadalafil (20 mg single dose) and doxazosin (8 mg daily), an alpha-1 adrenergic receptor blocker, there was an augmentation of the blood pressure–lowering effect of doxazosin. This effect was still present at 12 hours postdose and had generally disappeared at 24 hours. The number of subjects with potentially clinically significant standing–blood– pressure decreases was greater for the combination.
An additional study was performed with tadalafil (20 mg single dose) and doxazosin (4 and 8 mg daily) using ambulatory blood pressure monitoring. The augmentation appeared unrelated to dosing times and resulted in a greater number of outliers for the combination than had been observed in the previous study. Both of these studies had some symptomatology associated with these blood pressure changes.
A further study was carried out with doxazosin (up to 4 mg daily) added to tadalafil (5 mg daily) and there was again an augmentation of response. In this clinical pharmacology study there were symptoms associated with the decrease in blood pressure, including syncope.
An interaction study with tadalafil (20 mg single dose) and alfuzosin, also an alpha-1 adrenergic receptor blocker, showed no clinically significant effect on blood pressure.
In two clinical pharmacology studies in healthy volunteers, tadalafil (5 mg daily, and 10 mg and 20 mg single dose) had no clinically significant effect on blood pressure changes because of tamsulosin, a selective alpha-1a adrenergic receptor blocking agent.
Effects on Cardiac Electrophysiology
The effect of a single 100 mg dose of tadalafil (2.5 times the recommended dose) on the QT interval was evaluated at the time of peak tadalafil concentration in a randomized, double–blinded, placebo, and active–controlled (intravenous ibutilide) crossover study in 90 healthy males aged 18 to 53 years. The mean change in QTc (Fridericia QT correction) for tadalafil, relative to placebo, was 3.5 milliseconds (two–sided 90% CI=1.9, 5.1). The mean change in QTc (Individual QT correction) for tadalafil, relative to placebo, was 2.8 milliseconds (two–sided 90% CI=1.2, 4.4). In this study, the mean increase in heart rate associated with a 100 mg dose of tadalafil compared to placebo was 3.1 beats per minute.
Effects on Exercise Stress Testing
The effects of tadalafil on cardiac function, hemodynamics, and exercise tolerance were investigated in a single clinical pharmacology study. In this blinded crossover trial, 23 subjects with stable coronary artery disease and evidence of exercise–induced cardiac ischemia were enrolled. The primary endpoint was time to cardiac ischemia. The mean difference in total exercise time was 3 seconds (tadalafil 10 mg minus placebo), which represented no clinically meaningful difference. Further statistical analysis demonstrated that tadalafil was similar to placebo with respect to time to ischemia. Of note, in this study, in some subjects who received tadalafil followed by sublingual nitroglycerin in the post– exercise period, clinically significant reductions in blood pressure were observed, consistent with the augmentation by tadalafil of the blood–pressure–lowering effects of nitrates.
Effects on Vision
Single oral doses of PDE inhibitors have demonstrated transient dose-related impairment of color discrimination (blue/green), using the Farnsworth–Munsell 100–hue test, with peak effects near the time of peak plasma levels. This finding is consistent with the inhibition of PDE6, which is involved in phototransduction in the retina. In a study to assess the effects of a single dose of tadalafil 40 mg on vision (N=59), no effects were observed on visual acuity, intraocular pressure, or pupillometry. Across all clinical studies with tadalafil, reports of changes in color vision were rare (<0.1% of patients).
Effects on Sperm Characteristics
Three studies were conducted in men to assess the potential effect on sperm characteristics of tadalafil 10 mg (one 6-month study) and 20 mg (one 6-month and one 9-month study) administered daily. There were no adverse effects on sperm morphology or sperm motility in any of the three studies. In the study of 10 mg tadalafil for 6 months and the study of 20 mg tadalafil for 9 months, results showed a decrease in mean sperm concentrations relative to placebo, although these differences were not clinically meaningful. This effect was not seen in the study of 20 mg tadalafil taken for 6 months. In addition there was no adverse effect on mean concentrations of reproductive hormones, testosterone, luteinizing hormone or follicle stimulating hormone with either 10 or 20 mg of tadalafil compared to placebo.
Dose-Response Relationship
Dose-response relationships, between 20 mg and 40 mg, were not observed for 6-minute walk distance or pulmonary vascular resistance (PVR) in subjects with PAH in the placebo-controlled study. Median change from baseline in 6-minute walk distance was 32 meters and 35 meters at 16 weeks in subjects receiving 20 mg and 40 mg daily, respectively. Mean change from baseline PVR was -254 dynes*sec*cm-5 and -209 dynes*sec*cm-5 at 16 weeks in patients receiving 20 mg and 40 mg daily, respectively.