Drug Interactions between digoxin and Elspar

MONITOR: Concomitant use of asparaginase with other hepatotoxic agents may potentiate the risk of liver injury. Asparaginase-associated hepatotoxicity has been reported more commonly in adults than in children and has been strongly associated with obesity. Hepatomegaly, acute severe hepatotoxicity, and fatal liver failure have been reported with asparaginase treatment in adults. Also, asparaginase may increase the toxicity of drugs bound to plasma proteins or metabolized by the liver.

MANAGEMENT: The risk of additive hepatotoxicity should be considered when asparaginase is used with other hepatotoxic agents (e.g., alcohol, androgens, antituberculosis agents, azole antifungal agents, ACE inhibitors, macrolide antibiotics, nonsteroidal anti-inflammatory agents, nucleoside reverse transcriptase inhibitors, sulfonamides, thiazolidinediones, and statins). Liver function tests should be monitored at regular intervals during asparaginase treatment with or without other hepatotoxic drugs. Patients should be advised to seek medical attention if they experience potential symptoms of hepatotoxicity such as right upper quadrant pain, increasing abdominal size, fever, rash, itching, anorexia, nausea, vomiting, fatigue, malaise, dark urine, pale stools, and jaundice.

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.