Drug Interactions between cannabidiol and macitentan / tadalafil

MONITOR: Coadministration of cannabidiol with other agents known to induce hepatotoxicity may potentiate the risk of liver injury. Cannabidiol causes dose-related elevations of liver transaminases, both alanine aminotransferase (ALT) and aspartate aminotransferase (AST). In controlled studies, the incidence of ALT elevations above 3 times the upper limit of normal (ULN) was 13% with cannabidiol versus 1% with placebo, and 17% in patients taking cannabidiol 20 mg/kg/day compared to 1% taking 10 mg/kg/day. Less than 1% of cannabidiol-treated patients had ALT or AST levels greater than 20 times the ULN. Some cases required hospitalization. In clinical trials, serum transaminase elevations typically occurred within the first two months of treatment initiation, but up to 18 months were reported in some cases, particularly in patients taking concomitant valproate. Resolution occurred with discontinuation or dosage reduction of cannabidiol and/or concomitant valproate in about two-thirds of the cases. In about one-third of the cases, transaminase elevations resolved during continued cannabidiol treatment, without dose reduction. The majority of ALT elevations occurred in patients taking concomitant valproate. Concomitant use of clobazam also increased the incidence of transaminase elevations, but to a lesser extent. In cannabidiol-treated patients, the incidence of ALT elevations greater than 3 times the ULN was 30% in patients taking both concomitant valproate and clobazam, 21% in patients taking concomitant valproate (without clobazam), 4% in patients taking concomitant clobazam (without valproate), and 3% in patients taking neither drug. Insufficient data are available to assess the risk of concomitant administration of other hepatotoxic drugs. Finally, patients with baseline transaminase levels above the ULN also had higher rates of transaminase elevations during cannabidiol treatment. In patients taking 20 mg/kg/day in controlled trials, the frequency of treatment-emergent ALT elevations greater than 3 times the ULN was 30% when ALT was above the ULN at baseline, compared to 12% when ALT was within the normal range at baseline. No patient taking cannabidiol 10 mg/kg/day experienced ALT elevations greater than 3 times the ULN when ALT was above the ULN at baseline, compared with 2% of patients in whom ALT was within the normal range at baseline.

MANAGEMENT: Caution is advised if cannabidiol is used in patients who are currently receiving or have recently received treatment with other hepatotoxic agents, and vice versa. Serum transaminases and total bilirubin levels should be obtained prior to initiating cannabidiol, and patients with elevated baseline transaminase levels above 3 times the ULN accompanied by elevations in bilirubin above 2 times the ULN should be evaluated. Repeat levels should be obtained at 1 month, 3 months, and 6 months after initiation of cannabidiol treatment, and periodically thereafter or as clinically indicated (e.g., within 1 month following changes in cannabidiol dosage or addition of/changes in medications that are known to impact the liver). Consider more frequent monitoring of serum transaminases and bilirubin in patients who are taking valproate or who have elevated liver enzymes at baseline. Patients who develop clinical signs or symptoms suggestive of hepatic dysfunction (e.g., unexplained nausea, vomiting, right upper quadrant abdominal pain, fatigue, anorexia, jaundice, dark urine) should have serum transaminases and total bilirubin measured promptly, and cannabidiol treatment interrupted or discontinued as appropriate. Cannabidiol should be discontinued in patients with elevations of transaminase levels greater than 3 times the ULN and bilirubin levels greater than 2 times the ULN. Patients with sustained transaminase elevations of greater than 5 times the ULN should also have treatment discontinued. Patients with prolonged elevations of serum transaminases should be evaluated for other possible causes. Also consider dosage adjustment or discontinuation of any coadministered medication that is known to affect the liver.

Based on their pharmacology, phosphodiesterase-5 (PDE5) inhibitors may conceivably potentiate the hypotensive effect of antihypertensive medications or effects of agents with hypotensive properties. These agents inhibit PDE5-mediated degradation of cyclic guanosine monophosphate (cGMP), which in vascular smooth muscles can cause peripheral vasodilation. However, clinical pharmacology studies of tadalafil (administered as a 10 mg dose except in studies with angiotensin II receptor (AR) blockers and amlodipine, which used a dose of 20 mg) have demonstrated no clinically significant interaction with various antihypertensive drugs from major classes including calcium channel blockers, ACE inhibitors, beta blockers, thiazide diuretics, and AR blockers. Tadalafil 10 mg and 20 mg also had no clinically significant effect on blood pressure changes due to tamsulosin, an alpha-1a blocker. In addition, analysis of data from Phase 3 clinical trials showed no difference in adverse events in patients taking tadalafil with or without antihypertensive medications. In patients receiving concomitant antihypertensive medications, tadalafil 20 mg may induce a blood pressure decrease that is, in general, minor and not likely to be clinically relevant. In a clinical study of healthy male subjects 45 to 78 years of age, administration of silodosin with a single 20 mg dose of tadalafil resulted in increased frequency of positive orthostatic test results during a 12-hour period following concomitant dosing compared to administration with placebo. No events of symptomatic orthostasis or dizziness were reported in subjects receiving silodosin with tadalafil. Nevertheless, patients should be advised of the potential for interaction and to contact their doctor if they experience symptoms of hypotension such as dizziness, lightheadedness, or fainting.