Drug Interaction Report

MONITOR: Coadministration of opioids with anticholinergic agents may result in additive central nervous system (CNS), gastrointestinal, and genitourinary effects. The risk and/or severity of adverse effects such as sedation, dizziness, confusion, cognitive and psychomotor impairment, dry mouth, constipation, and urinary retention may increase. Severe constipation may lead to paralytic ileus in some cases.

MANAGEMENT: Caution and close monitoring of central nervous system, gastrointestinal, and genitourinary adverse effects are recommended when opioids are used with anticholinergic agents. Ambulatory patients should be counseled to avoid hazardous activities requiring mental alertness and motor coordination until they know how these agents affect them, and to notify their physician if they experience excessive or prolonged CNS effects that interfere with their normal activities.

Anticholinergic agents may increase the absorption and oral bioavailability of some digoxin formulations. The proposed mechanism involves increased gastrointestinal transit time due to reduction of stomach and intestinal motility by anticholinergic agents. In one study, coadministration with propantheline (15 mg three times a day for 10 days) led to a 30% mean increase in serum digoxin levels in 9 of 13 elderly women receiving a slow-dissolution formulation of digoxin. The interaction has also been reported with formulations containing large particle size digoxin. Other studies have found no significant effect of propantheline on digoxin elixir, solution in capsules, rapid-dissolution tablets, and micronized digoxin tablets. Therefore, the interaction is not expected to occur with most digoxin products used today in industrialized countries (e.g., Lanoxin). Due to the drug's narrow therapeutic index, however, clinicians may consider monitoring patients more closely for digoxin side effects and toxicity during coadministration with anticholinergic agents. Patients should be advised to notify their physician if they experience potential signs and symptoms of digoxin toxicity such as nausea, anorexia, visual disturbances, slow pulse, and irregular heartbeats.

GENERALLY AVOID: Ethanol may potentiate the central nervous system (CNS) depressant effects of opioid analgesics. Concomitant use may result in additive CNS depression and impairment of judgment, thinking, and psychomotor skills. In more severe cases, hypotension, respiratory depression, profound sedation, coma, or even death may occur.

MANAGEMENT: Concomitant use of opioid analgesics with ethanol should be avoided.

GENERALLY AVOID: Use of anticholinergic agents with alcohol may result in sufficient impairment of attention so as to render driving and operating machinery more hazardous. In addition, the potential for abuse may be increased with the combination. The mechanism of interaction is not established but may involve additive depressant effects on the central nervous system. No effect of oral propantheline or atropine on blood alcohol levels was observed in healthy volunteers when administered before ingestion of a standard ethanol load. However, one study found impairment of attention in subjects given atropine 0.5 mg or glycopyrrolate 1 mg in combination with alcohol.

MANAGEMENT: Alcohol should generally be avoided during therapy with anticholinergic agents. Patients should be counseled to avoid activities requiring mental alertness until they know how these agents affect them.

Administration of digoxin with a high-fiber meal has been shown to decrease its bioavailability by almost 20%. Fiber can sequester up to 45% of the drug when given orally. Patients should be advised to maintain a regular diet without significant fluctuation in fiber intake while digoxin is being titrated.

Grapefruit juice may modestly increase the plasma concentrations of digoxin. The mechanism is increased absorption of digoxin due to mild inhibition of intestinal P-glycoprotein by certain compounds present in grapefruits. In 12 healthy volunteers, administration of grapefruit juice with and 30 minutes before, as well as 3.5, 7.5, and 11.5 hours after a single digoxin dose (0.5 mg) increased the mean area under the plasma concentration-time curve (AUC) of digoxin by just 9% compared to administration with water. Moreover, P-glycoprotein genetic polymorphism does not appear to influence the magnitude of the effects of grapefruit juice on digoxin. Thus, the interaction is unlikely to be of clinical significance.