Drug Interactions between duloxetine and timolol

GENERALLY AVOID: Use of duloxetine in conjunction with chronic alcohol consumption may potentiate the risk of liver injury. Duloxetine alone can increase serum transaminase levels. In clinical trials, 0.3% of patients discontinued duloxetine due to liver transaminase elevations. The median time to detection was about two months. Three duloxetine-treated patients had liver injury as manifested by transaminase and bilirubin elevations, with evidence of obstruction. Substantial intercurrent ethanol use was present in each of these cases, which may have contributed to the abnormalities observed. Duloxetine does not appear to enhance the central nervous system effects of alcohol. When duloxetine and ethanol were administered several hours apart so that peak concentrations of each would coincide, duloxetine did not increase the impairment of mental and motor skills caused by alcohol.

MANAGEMENT: Due to the risk of liver injury, patients prescribed duloxetine should be counseled to avoid excessive use of alcohol. Duloxetine should generally not be prescribed to patients with substantial alcohol use.

MONITOR: Many psychotherapeutic and CNS-active agents (e.g., anxiolytics, sedatives, hypnotics, antidepressants, antipsychotics, opioids, alcohol, muscle relaxants) exhibit hypotensive effects, especially during initiation of therapy and dose escalation. Coadministration with antihypertensives and other hypotensive agents, in particular vasodilators and alpha-blockers, may result in additive effects on blood pressure and orthostasis.

MANAGEMENT: Caution and close monitoring for development of hypotension is advised during coadministration of these agents. Some authorities recommend avoiding alcohol in patients receiving vasodilating antihypertensive drugs. Patients should be advised to avoid rising abruptly from a sitting or recumbent position and to notify their physician if they experience dizziness, lightheadedness, syncope, orthostasis, or tachycardia. Patients should also avoid driving or operating hazardous machinery until they know how the medications affect them.

ADJUST DOSING INTERVAL: Concurrent administration with calcium salts may decrease the oral bioavailability of atenolol and possibly other beta-blockers. The exact mechanism of interaction is unknown. In six healthy subjects, calcium 500 mg (as lactate, carbonate, and gluconate) reduced the mean peak plasma concentration (Cmax) and area under the concentration-time curve (AUC) of atenolol (100 mg) by 51% and 32%, respectively. The elimination half-life increased by 44%. Twelve hours after the combination, beta-blocking activity (as indicated by inhibition of exercise tachycardia) was reduced compared to that with atenolol alone. However, during a 4-week treatment in six hypertensive patients, there was no difference in blood pressure values between treatments. The investigators suggest that prolongation of the elimination half-life induced by calcium coadministration may have led to atenolol cumulation during long-term dosing, which compensated for the reduced bioavailability.

MANAGEMENT: It may help to separate the administration times of beta-blockers and calcium products by at least 2 hours. Patients should be monitored for potentially diminished beta-blocking effects following the addition of calcium therapy.