Tolbutamide Dextropropoxyphene

Noninterfering acetaminophen, acyclovir, allopurinol, amoxicillin, amphotericin B, am-picillin, aspirin, azlocillin, bendrofluazide, bumetanide, buprenorphine, carbenidllin, cefazolin, cefotaxime, cefoxitin, ceftazidime, cefuroxime, cephalexin, chlorambucil, chloramphenicol, chlordiazepoxide, chlorpheniramine, chlorpropamide, cyclophosphamide, cyclosporin, C5d arabine, daunorubicin, dextropropoxyphene, dihydrocodeine, domperidone, flucytosine, furosemide, gentamicin, griseofulvin, melphalan, methotrexate, metochlo-pramide, metronidazole, miconazole, nabilone, netilmicin, nicotinamide, nitrazepam, penicillin G, piperacillin, prednisolone, procarbeizine, prochlorperazine, riboflavin, rifampin, sulfamethoxazole, thioguanine, tobramycin, tolbutamide, trimethoprim... 

Not understood. The effect dextropropoxyphene has on the metabolism of the warfarin enantiomers does not appear to have been studied. Dextropropoxyphene does not interact with other cytochrome P450 isoenzyme CYP2C9 substrates such as tolbutamide , (p.486), although it does interact with the CYP3A4 substrate carbamazepine , (p.527). There is also the possibility that the paracetamol component had some part to play (see also Coumarins + Paracetamol (Acetaminophen) , p.438). Alternatively, these eases may just represent idiosyncratic reactions. 

Dextropropoxyphene doe not appear to affect the pharmacokinetics of tolbutamide. Hypoglycaemia was seen in a patient taking an unnamed sulphonylurea with co-proxamol, and has also been reported in non-diabetic patients given dextropropoxyphene alone. 

Robson RA, Miners JO, Whitehead AG, Birkett DJ. Specificity of the inhibitory effect of dextropropoxyphene on oxidative drug metabolism in man effects on dieophylline and tolbutamide disposition. BrJ Clin Pharmacol ( 9S7) 23, 772-5. 

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