The minimum effective analgetic blood concentration of pethidine in patients with intractable pain.

1 Pethidine infusions were performed in 16 patients with intractable pain in order to define a minimum effective analgetic blood concentration (MEAC) range. 2 Pethidine blood concentrations at the return of pain following a period of analgesia were considered to provide a more useful estimation of the MEAC than that at the onset of analgesia. 3. The MEAC range found in 15 of the 16 patients was 0.10 mg/l to 0.82 mg/l (median 0.25 mg/l). The intravenous dose of pethidine used in this study did not provide analgesia in one patient. 4 If the MEAC was greater than 0.40 mg/l in any patient, then additional techniques were required to provide adequate long term analgesia, e.g. destructive neurolytic techniques or antidepressant therapy. 5 The pharmacokinetic properties of pethidine found in the majority of these patients were in the range considered to be normal. 6 The clinical pharmacokinetic properties of pethidine found in the majority of these patients were in the range considered to be normal. 6 The clinical pharmacokineticist has in important role to play in the investigation, diagnosis and treatment of patients with intractable pain by detecting those patients with atypical pharmacokinetic and/or pharmacodynamic characteristics towards analgesic drugs.