Drug Induced Thrombocytopenia

64 Drug induced thrombocytopenia can be caused by dozens of different medications and should be suspected in any patient who presents with acute thrombocytopenia of unknown origin. Typically, a patient will have taken the sensitizing drug for about 1 week or intermittently over a longer period of time before presenting with petechial hemorrhages and ecchymoses. Platelet inhibitors are the exception to this general rule because petechiae may occur within 1 or 2 days after an apparent first exposure. Systemic symptoms such as lightheadedness, chills, fever, nausea, and vomiting often precede bleeding. Severely affected individuals have florid purpura and bleeding from nose, gums and gastrointestinal or urinary tract. In adults, the presence of severe thrombocytopenia, with a platelet count < 20,000/uL, increases the likelihood that a patient has drug induced thrombocytopenia. If the causative medication is promptly discontinued, symptoms often resolve within 2 days and the platelet count returns to normal within a week. The medications most commonly associated with drug induced thrombocytopenia are listed below.

Analgesics

Acetaminophen
Diclofenac
Ibuprofen
Naproxen
Propoxyphene

Anticonvulsant & sedatives

Carbamazepine
Diazepam
Fentanyl
Phenytoin
Trimipramine
Valproic acid

Antimicrobial

Cephalosporins
Linezolid
Penicillins
Rifampin
Sulfonamides
Trimethoprim
Vancomycin

Cardiac

Amrinone
Beta blockers
Digoxin
Procainamide

Chemotherapeutic

Fludarabine
Oxaliplatin

Cinchona alkaloids

Quinine
Quinidine

Diuretics

Chlorothiazide
Furosemide
Hydrochlorothiazide

Heparins

Unfractionated
Low molecular weight

Histamine Receptor Antagonists

Cimetidine
Ranitidine

Immune Modulators

Cyclosporine
Interferon alpha & beta
Rituximab

Platelet Inhibitors

Abciximab
Clopidogrel
Dipyridamole
Eptifibatide
Tirofiban

Rheumatic

D-penicillamine
Gold salts
Infliximab

Many cases of drug induced thrombocytopenia are immune mediated and it is often possible to identify antibodies that react with normal platelets in the presence of the drug but not in its absence. In other cases with a high index of suspicion for drug induced thrombocytopenia, antibody tests are negative, probably because a drug metabolite produced in vivo, rather than the parent drug, is the sensitizing agent. Testing for drug induced platelet antibodies, with the exception of heparin, is technically demanding and only available at a few reference laboratories. Therefore, it is not useful in the immediate care of a patient.

When there is uncertainty about the causative drug, all medications should be discontinued, and pharmacologic equivalents with different chemical structures substituted as necessary. Patients who present with severe thrombocytopenia and wet purpura should be treated with platelet transfusions because of the risk of fatal intracranial and intrapulmonary hemorrhage. The therapeutic benefit of corticosteroids and intravenous immune globulin has not been proven. Once established, drug sensitivity probably persists indefinitely and patients should be advised to avoid permanently the suspected medication.

Last Updated on Monday, 18 July 2011