Fatal self-poisoning in the UK and the paracetamol/dextropropoxyphene combination

The relative lethal toxicity of pharmaceutical and illicit substances: A 16-year study of the Greater Newcastle Hunter Area, Australia

AIMS

We aim to calculate 2 metrics of relative lethal toxicity; the fatal toxicity index (FTI; number of deaths per year of a daily dose) and the case fatality (CF; number of deaths per overdose) with a focus on opioids, antidepressants, antipsychotics, benzodiazepines and illicit drugs.

METHODS

This descriptive cohort study used the Australian National Coronial Information System (NCIS) to identify a population of individuals with drug-associated deaths in the Greater Newcastle Hunter Area between January 2002 and December 2016. This was combined with Australian medicine dispensing data and corresponding data from the Hunter Area Toxicology Service to calculate FTI and CF.

RESULTS

There were 444 drug-related deaths and 21,296 overdoses during the study period. FTI and CF were well correlated (Spearman's rho 0.64, P < .001). Of the classes of interest, opioids had the highest FTI (40.3 95% confidence interval [CI] 35.2-45.4 deaths per 100 years of use at the defined daily dose or deaths/DDD/100 years) and CF (12.4% 95%CI 11.0-13.9). Fentanyl, methadone and morphine had the highest relative fatal toxicity within this class. Tricyclic antidepressants had the highest relative fatal toxicity of all antidepressants (FTI 14.5 95%CI 9.7-19.3 deaths/DDD/100 years and CF 7.1% [95%CI 4.8-9.3]) and benzodiazepines appeared to be more associated with multiple agent deaths than single. Of the illicit drugs, heroin had the highest CF (26.4%, 95%CI 19.1-33.7).

CONCLUSION

Knowledge of relative lethal toxicity is useful to prescribers and medicines and public health policy makers in restricting access to more toxic drugs and may also assist coroners in determining cause of death.

Does restricting pack size of paracetamol (acetaminophen) reduce suicides?

The authors discuss a new study that examined the change in deaths attributed to paracetamol poisoning in England and Wales in the six years before and after a legislated reduction in the maximum pack size.

A multicentre study of coproxamol poisoning suicides based on coroners' records in England

AIMS

To examine in detail a series of coproxamol overdose deaths in order to provide information that will assist in the development of strategies to prevent such fatalities.

METHOD

Inquest records in 24 coroners' jurisdictions in England on deaths between January 2000 and December 2001 which received a verdict of either suicide or undetermined cause (with a high or moderate probability of suicide) were examined.

RESULTS

One hundred and twenty-three coproxamol poisoning suicides were identified. Alcohol was involved in 58.5% of the overdoses and these individuals generally had lower blood drug levels and consumed fewer tablets. Younger people were more likely to have consumed alcohol and to have lower levels of suicide intent. Nearly half the individuals had a history of self harm, and a third were under psychiatric care. The coproxamol had been prescribed for the individual in 81.5% of cases, although only in 55.0% of those aged 10-34 years. In other cases the source of the coproxamol was nearly always a family member or partner. Some deaths resulted from relatively small overdoses.

CONCLUSIONS

Strategies to reduce self poisoning deaths due to coproxamol should take account of the high toxicity of coproxamol in overdose, especially when combined with alcohol, and the fact that risk of death extends beyond the person for whom the drug is prescribed.

Can the fatal toxicity of antidepressant drugs be predicted with pharmacological and toxicological data?

Antidepressant drugs are among the most common drugs involved in fatal poisoning and large variations between antidepressant drugs have been noted. Despite the fact that a large number of studies have calculated a fatal toxicity index (FTI) for antidepressants, no serious attempts have been made to compare the differences in fatal toxicity against known pharmacological and toxicological differences in receptor affinity. It is potentially from such data that screening of drugs during their pre-clinical development can be facilitated. We examined correlations between the FTI and noradrenaline (norepinephrine)/serotonin (5-hydroxytryptamine; 5-HT) reuptake inhibition selectivity, the dose that is lethal to 50% of animals (LD50), lipid solubility, and antagonist activity at cholinergic, histaminergic, alpha-adrenergic and gamma-aminobutyric acid (GABA)A receptors or sodium and potassium channel blocking effects. We obtained data on the number of fatal poisonings between 1983 and 1992 in England and Wales caused by a single antidepressant drug from the Department of Health in the UK. This number was divided by the number of prescriptions in England for these drugs over this time to derive a FTI of deaths per million prescriptions. The highest FTIs were for amoxapine, viloxazine, desipramine and dothiepin. Lofepramine, paroxetine and fluoxetine had very low FTIs. Using Poisson regression, there was a significant positive relationship between the FTI of antidepressant drugs and their lethal toxicity in animals, and measures of their cardiac effects. The relative noradrenaline/serotonin reuptake inhibition, lipid solubility and their potency at histamine H1, muscarinic and alpha 1-adrenergic receptors had no substantial association with the FTI. Limited data suggest that some cardiac effects and potency as a GABAA antagonist may be important predictors of significant toxicity. Further data using standardised bio-assays are needed to compare the direct cardiac effects of antidepressants. Thus, the best current pre-clinical indicator of fatal toxicity in humans is the LD50 in animal studies. Clearly, there are humane and practical reasons for developing a better pre-clinical indicator of toxicity in overdose for this rapidly expanding group of drugs.

Poisoning and epidemiology: 'toxicoepidemiology'

1. There is little hypothesis-testing clinical research performed in toxicology. Randomized clinical trials are rare and most observational studies are performed on highly selected patients and are subject to marked bias. Thus, for many poisonings, our approach has been based almost entirely on deduction from known pharmacological/toxicological effects, generalizations from drugs within the same therapeutic class, animal data and case reports. This is also far from satisfactory, as many toxicological mechanisms are poorly understood and not related to the therapeutic class. 2. Although we need much better data to address the clinical and public health aspects of poisoning, there are many practical and ethical reasons why randomized clinical trials are difficult in this field. However, the scope for observational research, in particular population-based clinical epidemiology, is almost unlimited. The collection of data on human poisoning is facilitated because most non-fatal overdoses are admitted to hospital and by legal requirements to report to the coroner deaths that are due to poisoning. In the present article I argue that 'toxicoepidemiology', meaning the application of epidemiological methods to the problem of acute poisoning, is the best means we have of addressing deficiencies in our knowledge of poisoning. 3. Examples are given of a variety of observational research strategies, ranging from audit to meta-analysis, that may be applied to clinical toxicology. From coronial and clinical data obtained from reasonably well-defined populations, it has been possible to identify a number of previously unrecognized differences in the severity and spectrum of toxicity between and within drug classes. Also, the demographic risk factors for poisoning and the reproducibility, validity and optimal use of diagnostic and therapeutic interventions can be assessed. 4. The major limitations to the range of associations and interventions that may be studied are the need to achieve adequate power to study uncommon outcomes or poisonings and the ability to replicate findings at other centres using similar methodology. The expansion of data collection to other centres has the potential largely to overcome these obstacles.

Relative toxicity of benzodiazepines in overdose

OBJECTIVE

To assess the sedative effects in overdose of temazepam and oxazepam compared with other benzodiazepines to determine if this explains reported differences in fatal toxicity.

DESIGN

Cohort study of patients admitted with benzodiazepine poisoning.

SETTING

Newcastle, Australia.

SUBJECTS

303 patients who had ingested benzodiazepine alone or in combination with alcohol and presented to a general hospital which served a well defined geographical area.

MAIN OUTCOME MEASURES

Degree of sedation: Glasgow coma score, McCarron Score, and whether patients were stuporose or comatose.

RESULTS

Oxazepam produced less and temazepam more sedation than other benzodiazepines. Unadjusted odds ratios for coma with oxazepam and temazepam compared with other benzodiazepines were 0.0 (95% confidence interval 0.0 to 0.85) and 1.86 (0.68 to 4.77) respectively, chi 2 = 7.08, 2df, P = 0.03. After adjustment for potentially confounding effects of age, dose ingested, and coingestion of alcohol, the odds ratios were 0.22 (0.0 to 1.43) for oxazepam and 1.94 (0.57 to 6.23) for temazepam. Similar results were obtained for other measures of sedation.

CONCLUSIONS

These results were in accordance with fatal toxicity indices derived from coroners' data on mortality and rates of prescription. The relative safety of benzodiazepines in overdose should be a consideration when they are prescribed.

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.

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.