Slow metabolism and long half life of methadone in a patient with lung cancer and cirrhosis.

In a patient on methadone maintenance treatment, admitted for lung cancer suspicion, a slight decrease in pain dose response to morphine have necessitated adjustments of methadone treatment founded on clinical check-up and methadone assay. Plasma methadone concentrations were 4 fold higher than mean plasma concentration for control population at the same dose. Half-life was above 70 hours and clearance and metabolic index were strongly decreased. In this patient, daily dose methadone occurred in progressive accumulation and neuro-physiological tolerance without clinical incidence, except decrease in morphine effectiveness compared to our knowledge. Cancer, cirrhosis and adjuvant therapy contributions (fluconazole, omeprazole) to this original methadone kinetic are discussed. Methadone and morphine dose clinical adjustments are described. However, the main objective of this case report is focused on plasma methadone assay contribution to therapeutic adjustment of the interval dose in a single patient with a complex clinical situation.