Methadone maintenance treatment is the most widely prescribed treatment for opiate dependence with proven benefits for patients. In France, 45,442 patients are treated by methadone syrup in 2012 with a mean dose of 60 mg/day (60% of methadone prescriptions) . This mean dose represents between one and three bottles used every day by each patient. The frequency of opiate substitution therapy in adults has tripled in the past decade. Nowadays, more than 50,000 bottles are used every day in France, most of which are thrown away in the bin. Nevertheless, some residents of areas where drug dealing is high as well as social workers have raised concern about empty bottles of methadone left behind in the streets, in the same way with that of syringes and pill boxes. Moreover, relatives at home, especially children, can have access to these empty bottles, either left behind or found in the bin.
In naïve users or in case of misuse, methadone can be a source of potentially lethal intoxications, resulting in fatal overdoses . A few cases of infantile intoxications have been described in the literature, some of which resulted in death [3–9]. In all those cases, methadone was not prescribed for infants; the children got intoxicated by taking methadone that had been carelessly stored by their parents or by parental administration of the drug . The following reasons may account for the delay in seeking help: methadone users may not realise the danger of the drug to children and may not know that there is an antidote. Secondly, parents may fear professional accusations of poor parenting. Therefore, the issue concerning the potential harmful effect of ‘empty or half empty’ bottles of methadone after use remains.
A report from the French Toxicovigilance Coordination Committee  carried out on the paediatric intoxications by methadone capsules and syrup between 2008 and 2012 in France reported 33 intoxications by methadone syrup, one of which was lethal, and 20 intoxications by methadone capsules (a total of 53 intoxications). The average age of the intoxicated children was 2 years old, and the average dose presumably swallowed was 15 mg with syrup forms. In most cases, the treatment was on a table, within the child's reach (bottles already opened or opened by the child). It should be noted that there was a case of intoxication in a public park, and four cases occurred in adolescents who did take methadone on purpose, to get ‘high’. It is not precisely mentioned if those subjects were naïve or tolerant. In terms of toxicity data, the toxic and potentially lethal methadone dose is 1 mg/kg for a naïve subject or for someone without acquired tolerance. In human subjects, the lowest published toxic dose (TDLo) ranges from 0.76 to 2 mg/kg, and the lowest published lethal dose (LDLo) is 1.3 mg/kg . We therefore consider that a dosage of 40 mg for an adult and of 10 mg for a child whose weight is 10 kg can be potentially lethal .
Is the residual quantity of methadone in the empty bottles insignificant or is there a risk of intoxication for someone who does not tolerate opiates, such as a child? In order to answer this question, we collected from bins a sample of bottles recapped after use by the patients taking their maintenance treatment in our addiction treatment program centre (CSAPA Espace Murger) located in the Fernand-Widal Hospital, Paris. The analysis of the methadone dosage left in these bottles was carried out in the toxicology laboratory of the Lariboisière Hospital in Paris.