Is thrombocytopenia a known adverse effect of trimethoprim or sulfamethoxazole? If so, how soon can

Fråga: Is thrombocytopenia a known adverse effect of trimethoprim or sulfamethoxazole? If so, how soon can it occur and is it reversible?

A 3-year-old girl has been prescribed trimethoprim-sulfamethoxazole (Bactrim) due to an urinary tract infection and otitis. After the second dose she had epistaxis during the night. Her hematological status is not available.

Sammanfattning: Thrombocytopenia is a very rare adverse effect of treatment with trimethoprim- sulfamethoxazole. The reaction can appear as early as after a few doses, even though it usually takes longer. The platelet count usually returns to normal after discontinuation of the drug and corticosteroid treatment.

Svar: Thrombocytopenia can be an adverse effect of the treatment with trimethoprim- sulfamethoxazole. There are 123 reports in the Swedish Drug Information System (1). There are also several reports in the literature (2). In a Danish study of drug-induced thrombocytopenia during 1968-1991, trimethoprim- sulamethoxazole was the most commonly reported drug (2). The relative risk in another, epidemiological study was estimated to be 38/1 miljon user-weeks (3). Thrombocytopenia associated with trimethoprim-sulfamethoxazole appears to be an immune-mediated reaction, resulting in destruction of platelets by drug-dependent platelet antibodies or hapten formation (4).

Thrombocytopenia usually occurs after 7-10 days of treament, but has been reported to appear already after a few doses (2, 4).

Usually the thrombocytopenia is reversible and the platelet counts return to normal soon after the trimethoprim- sulamethoxazole medication is withdrawn and corticosteroids given (1, 4). However in some cases platelet transfusion and intravenous immunoglobulin may be required (4, 5)

In the present case, where no platelet count is available, and where the nose-bleeding occurred already after the second dose, it is not possible to conclude whether the bleeding was related to either thrombocytopenia or trimethoprim-sulfamethoxazole treatment. 1 SWEDIS (the Swedish Drug Information System) 2 Pedersen-Bjergaard U, Andersen M, Hansen PB. Thrombocytopenia induced by noncytotoxic drugs in Denmark 1968-91. J Intern Med 1996;239(6):509-15. 3 Kaufman DW, Kelly JP, Johannes CB, Sandler A, Harmon D, Stolley PD, Shapiro S. Acute thrombocytopenic purpura in relation to the use of drugs. Blood 1993;82(9):2714-8. 4 Yamreudeewong W, Fosnocht BJ, Weixelman JM. Severe thrombocytopenia possibly associated with TMP/SMX therapy. Ann Pharmacother 2002;36(1):78-82. 5 Herrington A, Mahmood A, Berger R. Treatment options in sulfamethoxazole-trimethoprim-induced thrombocytopenic purpura. South Med J 1994;87(9):948-50.