15 December 2010

French study shows torsade rare to vanishing.

Perrin-Terrin A, Pathak A, Lapeyre-Mestre M. QT interval prolongation: prevalence, risk factors and pharmacovigilance data among methadone-treated patients in France. Fundam Clin Pharmacol. 2010 Sep 6;

Dear Colleagues,

These French authors have done our field a great service by replicating Anchersen’s national study from Norway which was so reassuring concerning the use of methadone in addiction treatment.

This study examined QT intervals in a small sample of methadone patients and then compared the results with national reports on adverse events involving methadone and/or cardiac issues including sudden death. These authors found a mean QT interval of 414 ± 29ms with no readings over 500ms, the level at which the risk of arrhythmia is believed to become significant. We are told that analysis of the 42 cases showed that longer QT intervals were associated with recent increases in methadone dose, tobacco smoking, the use of other medications and pre-existing cardiac disease. These findings are consistent with most other work published on this matter, with the notable exception of Wedam. The authors quote QT ‘dispersion’ which is the difference between the shortest and longest QT interval among the twelve leads readings on the standard cardiograph. Despite some initial promise, the significance of ‘dispersion’ has been questioned more recently and its relevance to methadone treatment is uncertain. Even normal values are not agreed upon by cardiologists.

The 550 reports to the official French ‘pharmcovigilence’ centre regarding methadone are of great interest and relevance to the current debate over supposed cardiac effects of methadone. In the ten years to 2007 only 5 reports (0.9%) involved QT problems, three of these with torsade de pointes including one death, a 19 year old who died after unsuccessful resuscitation. This case is not tabulated as having torsade but if he did, as implied in the text, he would represent the first confirmed death from torsade de pointes in the literature to my knowledge.

Over the ten years there were also 7 sudden deaths (1.3%) which the authors tabulate in detail. For some reason they postulate that some or all might be ascribed to arrhythmia. They state: “it is conceivable that serious toxicity might be mediated in part through cardiac effects rather than solely via respiratory depression.” Almost anything is ‘conceivable’ yet the real quesion is whether it is likely or even ‘credible’. In fact the data presented make it highly unlikely that torsade is involved to any significant degree, if at all. Were torsade the cause of just half of these deaths, and considering a reported mortality well under 10% (some say zero) then one would expect hundreds of non-fatal cases of torsade across France - yet only two were ever reported in the whole country over a ten year period. The expected under-reporting in such a voluntary scheme would apply to some extent to both mortality and torsade, even though the latter has become almost ‘notorious’ and was originally described in France and with a French name.

Further, these authors state of several deceased cases: ‘no overdose of methadone’. This is largely based on drug levels found at post-mortem. However, these are now known to be most unreliable alone in determining cause of death. Indeed, serious toxicity and death from narcotism have frequently been found with post-mortem blood methadone in the ‘therapeutic’ range while some patients in normal treatment have levels in or near the toxic range. Also, there are major changes in the levels of measurable methadone following death.

It seemed extraordinary that five of the deceased patients were being treated for psychosis so I wrote to the authors. I have now learned that certain antipsychotics are used commonly in France as alternatives to benzodiazepines, hence not all of these patients were schizophrenic. Each of these 5 patients who were prescribed anti-psychotics died in the first 5 days of methadone maintenance treatment for addiction and two were taking doses which were in excess of current guidelines. Nearly all were receiving four or more prescribed medications apart from the methadone. HIV drugs were involved in two cases. Hence these well-documented deaths also make it clear that polypharmacy is a major factor and the patients would have been self-evident as extremely high risk candidates for treatment.

This study makes it hard to understand the findings of Krantz who found more cases in his own small district than in the whole of France in a decade. Suffice it to say that the findings are even more reassuring than the national figures from Norway published by Anchersen and colleagues.

Comments by Andrew Byrne ..

Related article (includes one of the same authors): Molokhia M, Pathak A, Lapeyre-Mestre M, et al. Case ascertainment and estimated incidence of drug-induced long-QT syndrome: study in Southwest France. Br. J. Clin. Pharmacol. 2008 66:386–395

In this exhaustive paper using a rational methodology an estimate is made of the incidence of drug induced long QT syndrome (LQTS) at 11 per million per year. The literature shows that over 50% are due to class III antiarrhythmics (presumably in those with existing cardiac rhythm disturbances), closely followed by anti-infective drugs and antihistamines (with presumably some antipsychotics). The drug methadone is not even mentioned in the entire paper so we presume that in 2008 it was not even on the radar for these experienced and thorough researchers. This casts yet further doubt of the contention of Dr Mori Krantz that cardiac problems constitute a public health priority in methadone treatment in America.