Each week we will aim to bring out a concise email that provides 4-5 key pieces of information addressing a specific issue in clinical therapeutics.
This week: Drugs and Thrombocytopaenia
Duncan Yorkston, Clinical Pharmacist, Ward MM
Thrombocytopaenia is a common clinical condition characterised by low levels of platelets in the blood. Together with a low platelet count, other signs and symptoms may include easy bruising, fatigue and prolonged or unusual bleeding. Thrombocytopaenia may be caused by a variety of commonly prescribed medications which may either decrease platelet production or increase platelet destruction.
- Cytotoxics may commonly cause a decrease in platelet production via medication induced bone marrow suppression. Examples include methotrexate, hydroxycarbamide (hydroxyurea) and many types of chemotherapy.
- Increased platelet destruction is typically attributable to a mechanism known as drug induced immunologic thrombocytopenia (DITP). This condition is characterised by drug-dependent antibodies (DDAbs) that bind to platelets and cause their destruction.
- Many medications have been known to cause DITP including heparin, quinine, quinidine, penicillin, sulfonamides, sulfonylureas, NSAIDs, anticonvulsants, anti-rheumatic medications, gold salts, diuretics, rifampicin and ranitidine.
- Heparin is the most common cause of DITP and this situation requires prompt medical treatment due to the very high incidence of potentially life-threatening thrombosis.
- Treatment of suspected drug induced thrombocytopenia involves removal of the offending medication which typically results in a rapid rise in platelet count. In the case of heparin induced thrombocytopenia, danaparoid is recommended as an alternative. Low molecular weight heparins (LMWH) are not suitable as they may cross react with the implicated antibody.
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