Deaths from paracetamol and dextropropoxyphene (Distalgesic) poisoning in England and Wales in 1979

Co-proxamol and suicide: preventing the continuing toll of overdose deaths

Restricting means for suicide is a key element in suicide prevention strategies of all countries where these have been introduced. Preventing deaths from analgesic overdoses is highlighted in the National Suicide Prevention Strategy for England. The problem of self-poisoning with the prescription-only drug co-proxamol (dextropropoxyphene plus paracetamol) has received attention in several countries. We have conducted a review of the international literature related to possible strategies to tackle this problem. In England and Wales in 1997-1999, 18% of drug-related suicides involved co-proxamol; these constituted 5% of all suicides. Death usually results from the toxic effects of dextropropoxyphene on respiration or cardiac function. Death from co-proxamol overdose may occur rapidly, the lethal dose can be relatively low, and the effects are potentiated by alcohol and other CNS depressants. The majority of co-proxamol overdose deaths occur before hospital treatment can be received. The risk can extend to others in the household of the person for whom the drug is prescribed. While there is limited evidence that educational strategies have been effective in reducing deaths from co-proxamol poisoning, initiatives in Scandinavia, Australia and the UK to restrict availability of co-proxamol have produced promising results. Given the paucity of evidence for superior therapeutic efficacy of co-proxamol over other less toxic analgesics, there are good reasons to question whether it should continue to be prescribed.

Alcohol exposure and paracetamol-induced hepatotoxicity

Most instances of hepatotoxicity due to paracetamol in the United Kingdom and Australia are the result of large overdoses of the drug taken with suicidal or parasuicidal intent. In contrast, serious hepatotoxicity at recommended or near-recommended doses for therapeutic purposes has been reported, mainly from the United States and in association with chronic alcohol use, leading to the widely held belief that chronic alcoholics are predisposed to paracetamol-related toxicity at relatively low doses. Yet the effects of alcohol on paracetamol metabolism are complex. Studies performed in both experimental animals and humans indicate that chronic alcohol use leads to a short-term, two- to threefold increase in hepatic content of cytochrome P4502E1, the major isoform responsible for the generation of the toxic metabolite from paracetamol, although increased oxidative metabolism of paracetamol at recommended doses has not been demonstrated clinically. A reduced hepatic content of glutathione, required to detoxify the reactive metabolite, has been documented in chronic alcoholics, due probably to associated fasting and malnutrition, providing a metabolic basis for any possible predisposition of this group to hepatotoxicity at relatively low paracetamol doses. Simultaneous alcohol and paracetamol ingestion reduces oxidative metabolism of paracetamol in both rodents and humans, predominantly as a consequence of depletion in cytosol of free NADPH. The possibilities that chronic alcohol use may predispose to paracetamol-related hepatotoxicity and that alcohol taken with paracetamol may protect against it, based on these metabolic observations, are examined in this review.

Correlation between prescription of various dextropropoxyphene preparations and their involvement in fatal poisonings

In Sweden, the frequency of fatal poisoning by dextropropoxyphene (DXP) ingestion is constantly high. There are seven preparations containing DXP on the Swedish market; in three of them DXP is the sole analgesic ingredient, while four of them are combinations of analgesics. In an attempt to assess the death rate attributable to each DXP preparation on the basis of toxicological analyses, altogether 834 cases of dextropropoxyphene-related death over a 5-year period (1992-1996) in Sweden have been reviewed. The ratio between number of fatal poisonings and prescription of defined daily dose/1000 inhabitants during a 12-month period (DDD) was determined. The highest ratio, 27, was attributed to unmixed preparations. The ratio for DXP + paracetamol-related deaths was 6.3, and for DXP + phenazone, 6.4, while the lowest ratio, 2, was found among the DXP + chlorzoxazone cases. The unmixed preparations, representing 26% of all DXP prescriptions during the study years, were implicated in 62% of the DXP fatalities, a considerable over-representation. Unmixed preparations, with their higher content of DXP, may be more attractive for many consumers because of their narcotic (euphoric) effects rather than for any analgetic superiority. Another possibility is that unmixed preparations may erroneously have been regarded as safer than when combined with paracetamol, as reports of poisoning with compounds containing DXP + paracetamol have been most frequently reported, probably due to their predominance on the market.

Fatal poisonings attributed to benzodiazepines in Britain during the 1980s

The fatal toxicity indices of benzodiazepines during the 1980s were calculated from national prescribing data and mortality statistics. The overall rate was 5.9 deaths per million prescriptions for benzodiazepines taken alone or with alcohol only, anxiolytics being less toxic than hypnotics. Diazepam appeared more toxic than average among anxiolytics (P < 0.05), and flurazepam and temazepam more toxic than average among hypnotics (both P < 0.001). It was shown that the finding for diazepam was probably explained by concurrent use of alcohol, which implies that other anxiolytics may be safer in cases where there is alcohol misuse; but the greater toxicity of flurazepam and temazepam remained unexplained. Benzodiazepines are indeed much less toxic than the barbiturates they superseded, but they are not innocuous and temazepam in particular requires further evaluation.

Acute ethanol administration reduces the antidote effect of N-acetylcysteine after acetaminophen overdose in mice

1. The combined antidote effect of N-acetylcysteine and ethanol on the toxicity of acetaminophen was investigated. 2. Fed male mice were given acetaminophen i.p. (600 mg kg-1) and after 5 min in addition ethanol i.p. (0.2 ml, 19% v/v), N-acetylcysteine i.p. (1.2 g kg-1, 0.2 ml), N-acetylcysteine + ethanol i.p. (same doses as given individually) or saline i.p. (0.4 ml). Survival rates were determined after 24, 48, 72 and 96 h. 3. In the N-acetylcysteine group the survival rate was 85%. This rate was significantly reduced to 43% in the N-acetylcysteine + ethanol group (P = 0.0001). In the groups given ethanol or saline alone only 7% and 3%, respectively, survived 96 h. 4. The data suggest that the protective effect of N-acetylcysteine on acetaminophen-induced toxicity in fed mice is reduced by concomitant administration of ethanol. This may explain the clinical observation that ingestion of ethanol worsens the prognosis after acetaminophen intoxication.

Consumption, overdose and death from analgesics during a period of over-the-counter availability of paracetamol in Denmark

During the period 1978-1986, annual sales of paracetamol in Denmark increased from 1 million defined daily doses (DDD) (3 g) to 47 million DDD, while the number of admissions and deaths from overdose increased from 26 to 202 and from 1 to 3-4, respectively. The corresponding figures for salicylates are a decrease in sales from 113 to 94 million DDD, an increase in admissions from 282 to 595, and an increase in deaths from 5 to 22. From 1 January 1984 paracetamol became available on an over-the-counter basis. The figures for 1983 and 1984 were an increase in sales from 14 to 28 million DDD, an increase in admissions from 114 to 198, and an increase in deaths from 0 to 4. The number of deaths from opioid overdose remained constant at a value of about fifty during this period, the mortality per dose being about 20-fold higher than for paracetamol and salicylates. Dextropropoxyphene-related deaths increased twofold to 121 in 1986, with unchanged sales figures. A campaign launched by the National Board of Health resulted in a reduction in the number of deaths from dextropropoxyphene to 66 in 1987. The main effect of over-the-counter release of paracetamol was a dramatic increase in sales, without the epidemic of deaths observed a decade ago in the UK. It is suggested that the higher mortality of paracetamol poisonings in the UK compared to Denmark is related to the dextropropoxyphene content of the combination product, which is not available in Denmark. From an epidemiological toxicological viewpoint such combinations are not justified.

Marked QRS complex abnormalities and sodium channel blockade by propoxyphene reversed with lidocaine

The opiate analgesic propoxyphene produces cardiac toxicity when taken in overdose. We recently observed a patient with propoxyphene overdose in whom marked QRS widening was reversed by lidocaine. The reversal is apparently paradoxical as both agents block the inward sodium current (INa). We examined possible mechanisms of the reversal by measuring INa in rabbit atrial myocytes during exposure to propoxyphene and the combination of propoxyphene and lidocaine (60 and 80 microM, respectively). Propoxyphene caused use-dependent block of INa during pulse train stimulation. Block recovered slowly with time constants of 20.8 +/- 3.9 s. Block during lidocaine exposure recovered with time constants of 2-3 s. During exposure to the mixture, block recovered as a double exponential. The half time for recovery during exposure to the mixture was 1.6 +/- .9 s compared with a half-time of 14.3 +/- 2.9 s during exposure to propoxyphene alone. During pulse train stimulation, less steady-state block was observed during exposure to the mixture than during exposure to propoxyphene alone when the interval between pulses was greater than 0.95 s. Both drugs compete for a common receptor during the polarizing phase. The more rapid dissociation of lidocaine during the recovery period leads to less block during the mixture than during exposure to propoxyphene alone. The experiments suggest a mechanism for reversal of the cardiac toxicity of drugs which have slow unbinding kinetics.

Dextropropoxyphene overdose. Epidemiology, clinical presentation and management

This paper comprehensively reviews the worldwide situation regarding acute overdosage of dextropropoxyphene (propoxyphene). The changing epidemiology of this type of poisoning over the last 20 years is described with discussion of concurrent trends and, in particular, the effects of different preventive measures adopted in various countries. The clinical pharmacology of dextropropoxyphene relevant to the clinical toxic effects resulting from acute overdosage is described, and the management is detailed. In particular, the importance of early diagnosis and treatment is stressed in view of the potentially lethal complications that may suddenly occur with this poisoning. Recommendations for the correct use of the specific narcotic antagonist, naloxone, are made, together with other intensive supportive measures. As dextropropoxyphene is frequently taken together with other toxic agents, the concomitant effects of alcohol and sedative drugs are described and the treatment of paracetamol (acetaminophen) in combination with dextropropoxyphene is emphasised. The most effective preventive measures for the future are suggested, but caution is advised regarding the prescription for 'at risk' patients of alternative analgesics, which may be no safer in overdosage.

Non-narcotic analgesics. Problems of overdosage

The first cases of fulminant hepatic failure due to paracetamol poisoning were reported in 1966, and in the United Kingdom this condition is now responsible for more cases of acute hepatic failure than any other cause. Adults account for the majority of serious and fatal cases of paracetamol poisoning and it is extremely rare for young children to ingest sufficient paracetamol to cause more than minimal liver damage. A single measurement of the plasma paracetamol concentration is an accurate predictor of liver damage provided that it is taken not earlier than 4 hours after ingestion of the overdose. Peak disturbance of liver function occurs 2 to 4 days after the overdose, often accompanied by mild jaundice, after which recovery is usually rapid and complete. In a few patients, fulminant hepatic failure, manifested by increasing jaundice and encephalopathy, may develop by the third to fifth day. Acute renal failure may complicate paracetamol poisoning, often in the context of severe liver damage. Renal failure, which is often non-oliguric, typically becomes apparent 24 to 72 hours after overdosage. The treatment of paracetamol intoxication should include gastric lavage, which has been shown to be of value for up to 6 hours after ingestion of a paracetamol overdose. Further general treatment may include parenteral fluid replacement and a prophylactic infusion of dextrose (5-10%) in patients at risk of hepatic failure. Specific protective agents in those patients at risk of paracetamol-induced liver damage include N-acetylcysteine and methionine which are most effective if given within 8 to 10 hours of ingestion of the overdose. Hepatic and renal failure should be managed conventionally. In recent years in the United Kingdom there has been a gradual decline in the number of hospital admissions and the number of deaths from aspirin poisoning. Salicylates in overdose directly stimulate the respiratory centre and so cause a respiratory alkalosis. Metabolic acidosis occurs in severe poisoning because of impairment of the oxidative metabolism of energy substrates. At very high salicylate concentrations respiratory depression may occur, possibly associated with neuroglycopenia, adding respiratory acidosis to the worsening metabolic acidosis. In addition to a mixed acid-base disturbance, hypokalaemia and hypoglycaemia may be present. Nausea and vomiting increase the fluid deficit. If dehydration is sufficiently severe, decreasing cardiac output may hasten development of lactic acidosis and acute renal failure.(ABSTRACT TRUNCATED AT 400 WORDS)