A 43-year-old man, with several years´ anamnesis of suspected multiple sclerosis, has recently rece

Fråga: A 43-year-old man, with several years´ anamnesis of suspected multiple sclerosis, has recently received the diagnosis of antiphospholipid syndrome (an autoimmune disease). He is being treated with Waran (warfarin) because of multiple thrombotic events, and with Lioresal (baclofen) because of hemiparesis. According to FASS Lioresal should be prescribed with caution to elderly patients with spasticity of cerebral aetiology because of an increased risk of side-effects.

What is the background for the recommendation in FASS? Are there any documented interactions between warfarin and baclofen?

Sammanfattning: There are no documented interactions between warfarin and baclofen. Clinical data from a discontinued trial suggest that elderly stroke patients may be more prone to developing drowsiness during treatment with baclofen.

Svar: No documentation has been found in the literature concerning interactions between warfarin and baclofen. Baclofen is eliminated mainly (85 per cent) as unchanged compound and the rest is metabolised mainly by deamination (1).

The statement in FASS is according to the manufacturer (2) based on a study by Hulme and co-workers from 1985 (3). Seven of 10 elderly stroke patients with muscle spasticity experienced severe drowsiness while receiving baclofen (15-30 mg per day) in a double-blind crossover trial of baclofen against placebo. The trial was discontinued as they side-effects were considered unacceptable. In a subsequent pharmacokinetics study, reported in the same article, the pharmacokinetics of baclofen 10 mg given orally were studied in 12 elderly stroke patients and in 12 healthy younger subjects. No clear pharmacokinetic explanation was found for the increased drowsiness in the elderly. The mean elimination half-life of baclofen was, however, slightly longer in the elderly, which is consistent with the decreased renal function often seen in elderly individuals. An increased organ sensitivity to baclofen in the elderly was also suggested as a possible explanation for the increased drowsiness. 1 Brogden RN, Speight TM, Avery GS: Baclofen: a preliminary report of its pharmacological properties and therapeutic efficacy in spasticity. Drugs 1974; 8: 1-14 2 Personal communication, Mats Henning, Ciba-Geigy 3 Humle A, MacLennan WJ, Ritchie RT, John VA, Shotton PA: Baclofen in the Elderly Stroke Patient its Side-Effects and Pharmacokinetics. Eur J Clin Pharmacol 1985; 29: 467-469