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Letter to the editor
Editor, – In writing on the dental implications of the management of the post-infarct patient (Aust Prescr 1996;19:13), Dr R. Woods appears to have selectively quoted from his reference1 regarding antibiotics and warfarin. He states 'If antibiotics are employed, dentists should be aware that some antibiotics may inhibit the action of warfarin.' This is true for rifampicin, nafcillin, dicloxacillin1 and griseofulvin.2 Dr Woods has not mentioned that Buckley and Dawson1 also reported potentiation of warfarin by erythromycin, metronidazole, chloramphenicol, quinolones, trimethoprim/sulfamethoxazole, sulfonamides, the imidazole antifungals, some cephalosporins and high intravenous dose penicillin. This latter group includes antibiotics more likely to be prescribed by dentists as the former drugs are not on the Schedule of Pharmaceutical Benefits for dentists.3 Antibiotic potentiation of warfarin has also been referred to in the dental literature.4,5
A recent review concluded there was probable potentiation of warfarin by paracetamol and by dextropropoxyphene,6 and potentiation by aspirin was referred to by Buckley and Dawson.1 These are common drugs in dentistry. Given the number of patients on long-term anticoagulants, Dr Woods may care to elaborate on these important interactions.
Dentists should be mindful of both potentiation and inhibition of warfarin. The former is a potential dental emergency with respect to haemorrhage, the latter a potential medical emergency. I feel the evidence would lead dentists to be more concerned about potentiation of warfarin rather than inhibition and suspect this is by far the more likely problem that dentists may cause or have cause to deal with.
Lecturer in Periodontology
Faculty of Dentistry
University of Queensland
- Buckley NA, Dawson AH. Drug interactions with warfarin. Med J Aust 1992;157:479-83.
- Okino K, Weibert RT. Warfarin-griseofulvin interaction. Drug Intell Clin Pharm 1986;20:291-3.
- Commonwealth Department of Health and Family Services. Pharmaceutical benefits for dental use. In: Schedule of pharmaceutical benefits. Canberra:Australian Government Publishing Service, 1996:137-58.
- Wood GD, Deeble T. Warfarin: dangers with antibiotics. Dent Update 1993;20:350, 352-3.
- Wood GD. Antibiotic prescribing and warfarin enhancement [letter]. Br Dent J 1993;175:241.
- Wells PS, Holbrook AM, Crowther NR, Hirsh J. Interactions of warfarin with drugs and food. Ann Intern Med 1994;121:676-83.
- Majerus PW, Broze GJ Jr, Miletich JP, Tollefsen DM. Anticoagulant, thrombolytic and antiplatelet drugs. In: Goodman Gilman A, Rall TW, Nies AS, Taylor P, editors. Goodman and Gilman's the pharmacological basis of therapeutics. 8th ed. New York: Pergamon Press, 1990: 1311-31.