Interaction between carbamazepine and propoxyphene in man

Area of Science:

• Pharmacology
• Clinical Toxicology
• Neuropharmacology

Background:

• Clinical suspicion of drug interaction between Propoxyphene hydrochloride (PRX) and Carbamazepine (CBZ).
• Carbamazepine is commonly used for epilepsy and trigeminal neuralgia.
• Propoxyphene hydrochloride is an analgesic agent.

Purpose of the Study:

• To investigate the potential drug interaction between Propoxyphene hydrochloride and Carbamazepine.
• To assess the effect of Propoxyphene hydrochloride on Carbamazepine plasma levels in patients.

Main Methods:

• Seven outpatients (epilepsy/trigeminal neuralgia) on Carbamazepine treatment received Propoxyphene hydrochloride (65 mg TID).
• Monitoring for side effects and drug intoxication symptoms.
• Plasma Carbamazepine levels were analyzed using thin-layer chromatography.

Main Results:

• Two patients discontinued Propoxyphene hydrochloride due to severe side effects.
• Three patients exhibited symptoms of drug intoxication.
• A 45-77% increase in Carbamazepine plasma levels was observed in all patients co-treated with Propoxyphene hydrochloride.

Conclusions:

• Simultaneous administration of Carbamazepine and Propoxyphene hydrochloride leads to a significant increase in Carbamazepine plasma levels.
• Propoxyphene hydrochloride appears to inhibit the metabolism of Carbamazepine.
• This interaction poses a risk of Carbamazepine toxicity in patients using both drugs.