Methadone is a lipophilic drug with important tissue storage (fats, luing, ..) leading to a risk of delayed overdose during the days following initiation.

• Half-life : 22 hours but vary from 4 to 190 h with inter- and intra-individual variations . Usally, half life is around 14h for the first administration and 22h at steady state.

• Onset of analgesic effect: 30 to 60 minutes.

• Duration of analgesic effect: 3 to 6 hours at initiation then 8 to 12 hours with repeated administration.

• Metabolism by cytochrome P450, 2D6, 3A4, etc.

• Mutliple drug interactions (caution with new treatement introduced or stopped)

• No active metabolitesMajority eliminated in the faeces no adjustment for renal insufficiency