Procainamide-induced agranulocytosis with reversible myeloid sensitivity

When should the clinician suspect a drug-induced blood dyscrasia, and how should he proceed?

Blood dyscrasias account for only a minor fraction of all adverse drug reactions (ADRs), but are relevant because of their relatively high morbidity and mortality. For the majority of drugs, the magnitude of risk is low enough to remain undetected until wider distribution of the drug takes place. Thus, only post-marketing studies, carried out with appropriate methodology and sufficient statistical power, will allow the risk of serious haematological side-effects of new drugs to be ascertained. Publication of carefully studied and thoroughly described single case studies and reports to registries are necessary to detect new associations between drugs and blood dyscrasias, while only large cohort or case-control studies are suited to quantify the risks. Physicians managing a newly detected blood dyscrasia should be aware that it may be drug-induced. They should assess the exact diagnosis, obtain and thoroughly document a detailed exposure history and follow the blood counts after withdrawal of all potentially relevant agents. The recognition and appropriate management of the problem in individual cases is the basis for both effective patient care and the quality of subsequent pharmaco-epidemiological evaluation.

Drug treatment for myotonia

BACKGROUND

Abnormal delayed relaxation of skeletal muscles, known as myotonia, can cause disability in myotonic disorders. Sodium channel blockers, tricyclic antidepressive drugs, benzodiazepines, calcium-antagonists, taurine and prednisone may be of use in reducing myotonia.

OBJECTIVES

To consider the evidence from randomised controlled trials on the efficacy and tolerability of drug treatment in patients with clinical myotonia due to a myotonic disorder.

SEARCH STRATEGY

We searched the Cochrane Neuromuscular Disease Group trials register (April 2004), MEDLINE (January 1966 to December 2003) and EMBASE (January 1980 to December 2003). Grey literature was handsearched and reference lists of identified studies and reviews were examined. Authors, disease experts and manufacturers of anti-myotonic drugs were contacted.

SELECTION CRITERIA

We considered all (quasi) randomised trials of participants with myotonia treated with any drug treatment versus no therapy, placebo or any other active drug treatment. The primary outcome measure was:reduced clinical myotonia using two categories: (1) no residual myotonia or improvement of myotonia or (2) No change or worsening of myotonia. Secondary outcome measures were:(1) clinical relaxation time; (2) electromyographic relaxation time; (3) stair test; (4) presence of percussion myotonia; and (5) proportion of adverse events.

DATA COLLECTION AND ANALYSIS

Two authors extracted the data independently onto standardised extraction forms and disagreements were resolved by discussion.

MAIN RESULTS

Nine randomised controlled trials were found comparing active drug treatment versus placebo or another active drug treatment in patients with myotonia due to a myotonic disorder. Included trials were double-blind or single-blind crossover studies involving a total of 137 patients of which 109 had myotonic dystrophy type 1 and 28 had myotonia congenita. The studies were of poor quality. Therefore, we were not able to analyse the results of all identified studies. Two small crossover studies without a washout period demonstrated a significant effect of imipramine and taurine in myotonic dystrophy. One small crossover study with a washout period demonstrated a significant effect of clomipramine in myotonic dystrophy. Meta-analysis was not possible.

AUTHORS' CONCLUSIONS

Due to insufficient good quality data and lack of randomised studies, it is impossible to determine whether drug treatment is safe and effective in the treatment of myotonia. Small single studies give an indication that clomipramine and imipramine have a short-term beneficial effect and that taurine has a long-term beneficial effect on myotonia. Larger, well-designed randomised controlled trials are needed to assess the efficacy and tolerability of drug treatment for myotonia.

Drug metabolism by leukocytes and its role in drug-induced lupus and other idiosyncratic drug reactions

This review presents a unifying hypothesis that provides a connection between several types of hypersensitivity reactions associated with several types of drugs and explains some of the therapeutic effects (antiinflammatory activity and antithyroid effects) of these same drugs. This hypothesis centers on the oxidation of these drugs to chemically reactive metabolites by peroxidases. The drugs of interest have functional groups that are easily oxidized. The major peroxidase involved in this hypothesis is MPO because of its critical location in leukocytes which play a key role in the function of the immune system. However, thyroid peroxidase can probably also oxidize many of the same drugs to reactive metabolites, and this may be responsible for the thyroid autoimmunity observed in connection with some hypersensitivity reactions. Peroxidases have also been described in the skin and in platelets, and their presence may be responsible for the high incidence of skin reactions in the hypersensitivity response and the occurrence of immune-mediated thrombocytopenia, respectively. Involvement of other peroxidases, such as prostaglandin peroxidase, may also be important for antiinflammatory effects of drugs. In addition, leukocytes contain prostaglandin synthetase, and the activation of leukocytes leads to the release of arachidonic acid and the production of prostaglandins. This process may also lead to the metabolism of drugs to reactive metabolites. In studies of the metabolism of procainamide and dapsone, aspirin and indomethacin did not inhibit the formation of the hydroxylamine by neutrophils and mononuclear leukocytes. This is evidence against the involvement of prostaglandin synthetase in these oxidation; however, preliminary studies with other drugs suggest that prostaglandin synthetase may contribute to the metabolism of some drugs by leukocytes. Furthermore, the metabolism of phenylbutazone, phenytoin, and tenoxicam, as well as our preliminary work with other drugs such as carbamazepine, suggests that the range of drugs that are metabolized to reactive metabolites by peroxidases may be broader than initially suspected. There are several other drugs that do not fit into the functional group classes covered in this review but have similar properties. A good example is alpha-methyldopa, which is associated with drug-induced lupus, immune-mediated hemolytic anemia, and other hypersensitivity reactions. Such drugs may also be metabolized to reactive metabolites by peroxidases. Another aspect of the hypothesis is that an infection, or other inflammatory condition, may be an important risk factor for a hypersensitivity reaction because such a stimulus leads to activation of leukocytes which can lead to formation of reactive metabolites from certain drugs.(ABSTRACT TRUNCATED AT 400 WORDS)

Idiosyncratic drug reactions: possible role of reactive metabolites generated by leukocytes

Idiosyncratic drug reactions represent a poorly understood problem with serious medical implications. Many idiosyncratic drug reactions appear to be hypersensitivity reactions that involve an immune mechanism. The initiating step appears to involve the formation of a chemically reactive metabolite which can act as a hapten. Although the major site of drug metabolism is the liver, we have found that leukocytes, which contain myeloperoxidase and can generate hydrogen peroxide when stimulated, can also generate reactive metabolites. This has obvious implications for such idiosyncratic reactions as agranulocytosis. Furthermore, because of the importance of monocytes in the processing of antigen and the presentation of antigen to T lymphocytes in the initiation of an immunological reaction, formation of reactive metabolites by monocytes may also have implications for other idiosyncratic reactions such as drug-induced lupus and generalized idiosyncratic reactions.