Propoxyphene pharmacokinetics

Enantiomers may interact with one another at both pharmacokinetic and pharmacodynamic levels." One of the earlier and more interesting examples of such interactions was that of propoxyphene enantiomers. The analgesic activity of propoxyphene is due mainly to the d enantiomer. However, at least in the rat, the racemate is more potent than an equimolar dose of i/-propoxyphene due to a reduced clearance of the latter caused by the presence of / enantiomer in the racemate. 

Musa MN, Lyons LL. Effect of food and liquid on the pharmacokinetics of propoxyphene. Curr TherRes (1976) 19, 669-74. 

Cimetidine 1.2 g daily for 5 days had no effect on the pharmacokinetics of a single 120-mg dose of terfenadine in 12 healthy subjects. Another study in two groups of 6 healthy subjects confirmed that cimetidine 600 mg every 12 hours or ranitidine 150 mg every 12 hours had no effect on the pharmacokinetics of terfenadine 60 mg every 12 hours. No adverse ECG changes were seen. However, an isolated case report describes a 63-year-old woman who had 8 episodes of syncope (later identiiied as being due to torsade de pointes) and a convulsion 2 days after starting terfenadine 60 mg twice daily and cimetidine 400 mg twice daily. She was also taking chiorphenamine and co-proxamol (paracetamol (acetaminophen) and dextropropoxyphene (propoxyphene)). ... 

Determination of Unlabeled and Deuterium-Labeled Propoxyphene in Plasma. Measurement of Steady-State Pharmacokinetics in Dogs... 

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