Paracetamol overdose is the commonest cause of intentional self harm in the United Kingdom, accounting for approximately 70 000 cases per year.1 It is the commonest cause of acute liver failure,1 although this is rare in adults if doses of <12 g are ingested.2 To reduce this major health problem the government introduced legislation in September 1998 to limit the number of tablets in a single packet to 32 for packets sold in pharmacies and 16 in non-pharmacy outlets.3
This study assesses the impact of reduced availability of paracetamol on the number and severity of overdoses by comparing self poisoning cases in two periods of six months before and after the change to smaller packets.
Subjects, methods, and results
Patients presenting with acute self poisoning to five general hospitals in the Belfast area during the months January to June in 1998 and 1999 were included in the study. For each case we estimated the amount of paracetamol ingested, whether as a single agent or with other drugs. Where appropriate we recorded concentrations of serum paracetamol and liver enzymes, the international normalised ratio, and whether an antidote was given. We also recorded the numbers of patients admitted to hospital, patients transferred to a specialist unit, and deaths related to paracetamol overdose. We used a χ2 test to compare the numbers of patients admitted to hospital and the numbers who received an antidote during the two periods. A Mann-Whitney U test was used to compare the difference in estimated quantity of paracetamol ingested, serum concentration of paracetamol at 4-6 hours after the time of poisoning, and transaminase concentrations and the international normalised ratio at 24-48 hours.
Serum paracetamol concentrations were measured in 59% of the 590 patients who presented in the first period and 63% of 594 in the second. The estimated quantity of paracetamol ingested, the number of patients receiving the antidote, and the serum paracetamol concentration at 4-6 hours were significantly lower in the second period (table).
Two patients were transferred to a tertiary referral centre in 1998 and three in 1999. In 1998 neither patient required liver transplantation and both made a full recovery. However, in 1999 only one patient recovered completely; one died and one received a liver transplant.
Comment
Overdose behaviour changed after the introduction of smaller blister packs of paracetamol. The estimated quantity of paracetamol ingested was reduced; this measure is often unreliable, but in this study it was associated with a reduction in paracetamol concentration at 4-6 hours and decreased use of antidote. Early administration of the antidote was probably the reason why tests of liver function revealed no changes after the introduction of smaller packets. Unlike Prince et al,4 we found no reduction in the number of severe paracetamol overdoses; the only benefit we noted was a reduction in costs because fewer antidotes were given and there were fewer hospital admissions.
As in other studies on the impact of reducing the availability of paracetamol,4,5 a cause and effect relationship could not be identified. A number of factors—notably a change in medical practice and case mix—could have influenced the results. Although necessarily retrospective, this study has a number of strengths that make it more likely that the findings represent a change in overdose behaviour: there was a single observer, almost all cases of poisoning were identified, there was a time lag of three months between the date of law change and the second study period, and relatively objective measures were compared (number of admissions, paracetamol concentration, and use of antidote).
We conclude that measures to restrict the availability of paracetamol have reduced the amount taken in single overdoses but not the incidence of severe liver failure.
Table.
Cases of paracetamol overdose before and after the change to smaller packets (September 1998). Figures are medians (interquartile ranges) unless stated otherwise
| Jan-Jun 1998 (n=590) | Jan-Jun 1999 (n=594) | P value
|
||
|---|---|---|---|---|
| Mann- Whitney U test |
χ2 test | |||
| Estimated quantity of paracetamol ingested (g) | 10 (5-18) | 8 (5-14) | 0.004 | – |
| Serum paracetamol concentration (mg/l) at 4-6 hours | 37 (14-80) | 27 (6-64) | 0.003 | – |
| No (%) of patients admitted to hospital | 398 (67.4) | 374 (63.2) | – | 0.17 |
| No (%) of patients given antidote* | 183 (31.1) | 149 (25.1) | – | 0.03 |
| International normalised ratio at 24-48 hours | 1.1 (1.0-1.2) | 1.1 (1.0-1.2) | 0.50 | – |
| Concentration of liver enzyme† at 24-48 hours (U/l) | 23.0 (18-37) | 23.5 (19-52) | 0.84 | – |
N-acetylcysteine or methionine.
Serum aspartate aminotransferase.
Footnotes
Funding: No additional funding.
Competing interests: None declared.
References
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