Mebhydrolin induced agranulocytosis

Drug-induced agranulocytosis

Agranulocytosis is a rare but potentially serious adverse side effect of many drugs. Although it was recognised as an idiosyncratic type of drug reaction more than 50 years ago, its pathogenesis is still not fully understood. Drug-related antibodies are responsible for the neutropenia in the so-called 'immune' or 'aminopyrine' type of agranulocytosis. In contrast to former assumptions, the disappearance of leucocytes is not only due to rapid destruction of circulation cells, but it can result also from failure of the production of granulopoetic cells. In some other groups of drugs there is no evidence of immune-mediated disease, but direct toxicity to bone marrow cells has been observed using biochemical methods or inhibition of the growth of granulopoetic colonies in semisolid culture media. Until now it has not been possible to define the enzymatic abnormality which could explain this metabolic type of idiosyncrasy. The quantification of the incidence of potentially drug-induced agranulocytosis in general, and in particular its association with single drugs, requires studies on large populations and the use of strict epidemiological methodology to prevent reporting of grossly biased results. Data from recent case control studies show definitely lower risks for some relevant groups of drugs than formerly appreciated. As expected, agranulocytosis has been observed in association with some recently introduced drugs. This underlines the necessity for continued postmarketing monitoring of potential haematological side effects and for further case control studies to furnish data to aid prescribing physicians and health authorities in decision-making.

The CFU-C assay in patients with neutropenia and, in particular, drug associated neutropenia

One-hundred and four patients with a diagnosis of aplastic anaemia (28) or neutropenia (76) referred to our laboratory for assessment of granulopoiesis were studied. Bone marrow myeloid progenitor cell (CFU-C) frequency was measured and in 85 patients, inhibitor studies with either in-vitro drug addition or plasma co-culture were performed. Of 28 patients with aplastic anaemia, 22 (79%) had low numbers of CFU-C, while four (14%) had numbers within the normal range and two (7%) had elevated progenitor cell frequency. In contrast, of the 76 patients with neutropenia who were studied only 29 (38%) had low CFU-C numbers, 33 (43%) had a CFU-C frequency within the normal range and 14 (18%) had elevated CFU-C numbers. Thirty-nine patients had ingested potentially myelotoxic drugs and in eight of these it was possible to demonstrate drug associated inhibition of CFU-C proliferation in vitro. The drugs most commonly associated on a historical basis with myelosuppression were chloramphenicol, antimalarials, sulphonamides, anticonvulsants and nonsteroidal anti-inflammatory agents.

Drug-induced aplastic anaemia and agranulocytosis. Incidence and mechanisms

Aplastic anaemia and agranulocytosis are uncommon but serious adverse effects of drug therapy. They result from an adverse interaction between the drug and the haemopoietic pathway in certain susceptible individuals. The nature of this idiosyncratic interaction differs for different drugs and possibly for different individuals. In some instances an immune mechanism might be implicated, in others the patient's cells might carry a genetic susceptibility to the drug, while yet other patients might metabolise the drug abnormally. The idiosyncratic nature of these effects has made their investigation difficult, but experimental studies have allowed some progress in our understanding. In a practical sense, however, responsibility for preventing these problems will remain with clinicians, who should be alert to the risks and revise their prescribing habits accordingly.