Adverse hematologic effects of drugs

Drug-induced immune thrombocytopenia

Thrombocytopenia can have several causes, including the use of certain drugs. The mechanism behind drug-induced thrombocytopenia is either a decrease in platelet production (bone marrow toxicity) or an increased destruction (immune-mediated thrombocytopenia). In addition, pseudothrombocytopenia, an in vitro effect, has to be distinguished from true drug-induced thrombocytopenia. This article reviews literature on drug-induced immune thrombocytopenia, with the exception of thrombo-haemorrhagic disorders such as thrombotic thrombocytopenic purpura and heparin-induced thrombocytopenia and thrombosis. A literature search in PubMed combined with a check of the reference lists of all the retrieved articles resulted in 108 articles relevant to the subject. The drug classes that are most often associated with drug-induced immune thrombocytopenia are cinchona alkaloid derivatives (quinine, quinidine), sulfonamides, NSAIDs, anticonvulsants, disease modifying antirheumatic drugs and diuretics. Several other drugs are occasionally described in case reports of thrombocytopenia; an updated review of these case reports can be found on the internet. A small number of epidemiological studies, differing largely in the methodology used, describe incidences in the magnitude of 10 cases per 1 000 000 inhabitants per year. No clear risk factors could be identified from these studies. The underlying mechanism of drug-induced immune thrombocytopenia is not completely clarified, but at least three different types of antibodies appear to play a role (hapten-dependent antibodies, drug-induced, platelet-reactive auto-antibodies and drug-dependent antibodies). Targets for drug-dependent antibodies are glycoproteins on the cell membrane of the platelets, such as glycoprotein (GP) Ib/IX and GPIIb/IIIa. Diagnosis of drug-induced immune thrombocytopenia may consist of identifying clinical symptoms (bruising, petechiae, bleeding), a careful evaluation of the causal relationship of the suspected causative drug, general laboratory investigation, such as total blood count and peripheral blood smear (to rule out pseudothrombocytopenia), and platelet serology tests. The sensitivity of these tests is dependent on factors such as the concentration of the drug in the test and the potential sensitisation of the patient by metabolites instead of the parent drug. Drug-induced immune thrombocytopenia can be treated by withholding the causative drug and, in severe cases associated with bleeding, by platelet transfusion. Although drug-induced thrombocytopenia is a relatively rare adverse drug reaction, its consequences may be severe. Therefore it is important to extend our knowledge on this subject. Future research should focus on the identification of potential risk factors, as well as the exact mechanism underlying drug-induced thrombocytopenia.

The effect of lithium on platelet count

The effect of lithium on platelet count was studied by examining 12 patients treated with lithium carbonate without any additional medication, 13 patients treated with lithium carbonate with additional psychotropic medication, 25 patients with major affective disorder prior to any treatment, 25 patients with panic disorder prior to any treatment and 25 healthy controls. The platelet counts were increased in the group of subjects treated with lithium carbonate without any additional psychotropic medication. The increase was not clinically significant.

Immunology of adverse drug reactions

Adverse reactions to drugs often include an immunologic response. An understanding of immunologic mechanisms is useful in understanding the clinical manifestations of drug allergy. Predisposing factors to the development of allergic reactions to drugs include host factors as well as drug factors. Immune response relates to what we know about the components of the immune system as well as their differentiation and maturation processes. Immunologic reactions are often classified as Type I, Type II, Type III or Type IV, and these reaction types often correlate with clinical manifestations. For each reaction type the mechanism, drugs implicated, clinical manifestations, and treatment can be described.

Graft-versus-host reaction: a pathogenetic principle for the development of drug allergy, autoimmunity, and malignant lymphoma in non-chimeric individuals. Hypothesis

It is proposed that the same diseases as those induced by the graft-versus-host reaction (GVHR) will arise in nonchimeric individuals, if structures of the major histocompatibility complex (MHC) on lymphocytes are altered, either by viral infection or by chemicals, in such a way that autologous T lymphocytes react against them as the react in the GVHR to semiallogeneic (F1) lymphocytes differing at the MHC. Diseases in which a GVHR-like pathogenesis is suspected will be discussed.

Diphenylhydantoin-induced serum sickness with fibrin-platelet thrombi in lymph node microvasculature

In this 16 year old boy a syndrome, characterized by high fever, generalized lymphadenopathy, splenomegaly, diffuse skin rash, facial and periorbital edema, neutropenia, thrombocytopenia, elevated serum glutamic oxaloacetic transaminase (SGOT) levels and transient electrocardiographic changes, appeared 2 weeks after the institution of diphenylhydantoin therapy. Lymph node biopsy, performed at the height of the illness, revealed widespread subendothelial fibrin exudation and fibrin-platelet thrombi in the lymph node microvasculature, a finding most consistent with thrombotic thrombocytopenic purpura. Although many types of abnormal lymph node histology have been described with diphenylhydantoin, this appears to be the first instance of this histologic picture. This syndrome may be related to a serum sickness-like illness which triggered an episode of localized coagulopathy.