Drug Interaction Report

A single case report suggests that the combination of cyclophosphamide and indomethacin may cause serious hyponatremia. It is well known that cyclophosphamide alone can cause hyponatremia by causing a renal tubular concentrating defect, as well as a syndrome that resembles the syndrome of inappropriate antidiuretic hormone secretion (SIADH). Indomethacin may contribute to acute water intoxication by inhibiting synthesis of prostaglandins (which are important in maintaining water and electrolyte homeostasis and renal blood flow). However, it is not known whether indomethacin or other nonsteroidal anti-inflammatory drugs (NSAIDs) potentiate any side effects from cyclophosphamide. More data are needed.

GENERALLY AVOID: The concurrent use of aspirin or nonsteroidal anti-inflammatory drugs (NSAIDs) and ethanol may lead to gastrointestinal (GI) blood loss. The mechanism may be due to a combined local effect as well as inhibition of prostaglandins leading to decreased integrity of the GI lining.

MANAGEMENT: Patients should be counseled on this potential interaction and advised to refrain from alcohol consumption while taking aspirin or NSAIDs.