Drug Interaction Report

MONITOR: Theoretically, concomitant use of taurine and antihypertensive agents, vasodilators, or agents with hypotensive properties may have additive blood pressure-lowering effects. The proposed mechanism has not been established but has been suggested, primarily through studies in animal models, that taurine has a homeostatic function on vascular smooth muscle and cardiac muscle. Several mechanisms by which taurine has been proposed to promote vasodilation include effects on the nitric oxide system, endothelial function, and inhibition of the renin-angiotensin-aldosterone and sympathetic systems. A 2018 meta-analysis reviewing the effects of orally administered taurine on resting systolic blood pressure (SBP) and diastolic blood pressure (DBP) in humans showed that, in the 7 studies that met the inclusion criteria, treatment with oral taurine led to a statistically significant improvement in SBP and DBP compared with placebo. The mean reduction in blood pressure was approximately 3 mmHg for both systolic and diastolic readings, with a range of 0 to 15 mmHg and 0 to 7 mmHg for SBP and DBP, respectively. The effects of taurine supplementation may also be more significant in those who are pre-hypertensive or hypertensive compared to those with normal or moderately low blood pressure, regardless of their health status. However, clinical data are limited.

MANAGEMENT: Caution and monitoring for hypotension are recommended if oral taurine supplements are used in combination with antihypertensives, or agents with hypotensive properties. Patients should be advised to contact their physician if they experience symptoms of hypotension such as dizziness, lightheadedness, or fainting.

GENERALLY AVOID: Additive hypotensive effects may occur when phosphodiesterase-5 (PDE5) inhibitors such as tadalafil are used with alcohol, as both are mild systemic vasodilators. In clinical pharmacology studies, more subjects administered alcohol at a dose of 0.7 g/kg (equivalent to approximately 6 ounces of 80-proof vodka in an 80-kg male; consumed within 10 minutes in study subjects, providing blood alcohol levels of 0.08%) in combination with tadalafil 10 or 20 mg single doses had clinically significant decreases in blood pressure than with alcohol alone. There were reports of postural dizziness, and orthostatic hypotension was observed in some. When tadalafil 20 mg was administered with alcohol at a lower dose of 0.6 g/kg (equivalent to approximately 4 ounces of 80-proof vodka in an 80-kg male), orthostatic hypotension was not observed, dizziness occurred with similar frequency relative to alcohol alone, and the hypotensive effects of alcohol were not potentiated. Neither tadalafil nor alcohol affected the plasma concentrations of the other.

GENERALLY AVOID: Coadministration with grapefruit juice is likely to increase the plasma concentrations of tadalafil, which is primarily metabolized by CYP450 3A4. However, the interaction has not been studied. The proposed mechanism is inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall by certain compounds present in grapefruit.

MANAGEMENT: Patients taking tadalafil should avoid consuming large amounts of alcohol (for example, 5 units or more), which may increase the potential for orthostatic signs and symptoms including increase in heart rate, decrease in standing blood pressure, dizziness, and headache. It may also be appropriate to avoid consuming large amounts of grapefruit juice.