[Syncope with long QT interval in a 39 day-old infant treated with cisapride]

Area of Science:

• Pediatric Pharmacology
• Clinical Toxicology
• Drug Safety

Background:

• Cisapride is a prokinetic agent used for gastrointestinal motility disorders.
• Ranitidine is a histamine H2 receptor antagonist.
• Potential drug interactions and adverse effects, particularly cardiotoxicity, require careful consideration.

Observation:

• A 37-day-old infant treated with high-dose cisapride (1.2 mg/kg/d) and ranitidine presented with malaise.
• The infant exhibited a prolonged QT interval and ventricular extrasystoles upon admission.
• Cardiac abnormalities resolved after discontinuation of cisapride.

Findings:

• The observed cardiotoxicity, including prolonged QT interval, was likely linked to cisapride.
• High dosage of cisapride and potential metabolism inhibition by ranitidine may have contributed to the adverse event.
• Plasma concentration of cisapride was not measured, limiting definitive pharmacokinetic conclusions.

Implications:

• This case highlights the critical importance of appropriate cisapride dosing in infants.
• The potential for a drug interaction between cisapride and ranitidine, leading to cardiotoxicity, warrants further investigation.
• Healthcare providers should exercise caution when co-prescribing these medications in pediatric populations.