[Pharmacokinetics of pethidine after spinal anesthesia. Clinical implications]

Intrathecal pethidine: pharmacology and clinical applications

Pethidine is the only member of the opioid family that has clinically important local anaesthetic activity in the dose range normally used for analgesia. Pethidine is unique as the only opioid in current use that is effective as the sole agent for spinal anaesthesia. In lower doses, intrathecal pethidine is also an effective analgesic for treating pain in labour. This paper reviews the pharmacology of intrathecal pethidine and clinical experience reported to date. Articles reviewed include those identified by a Medline search using keywords "intrathecal" or "spinal anaesthesia/ anesthesia" and "pethidine" or "meperidine". Reference lists from identified papers were scrutinized to identify further relevant articles.

Clinical and pharmacokinetic aspects of the combination of meperidine and prilocaine for spinal anaesthesia

The aim of this study was to determine whether the addition of a small dose of prilocaine could augment the spinal block induced by meperidine and affect intrathecal meperidine pharmacokinetic behaviour. Spinal anaesthesia was performed in 60 men scheduled for endoscopic resection of a prostatic adenoma or bladder tumour under spinal anaesthesia. They were allocated randomly to receive either 1 mg.kg-1 meperidine (Group 1, n = 30), or 1 mg.kg-1 meperidine plus 0.5 mg.kg-1 prilocaine (Group 2, n = 30). Blood samples were collected prior to and for 24 hr after spinal injection in 24 patients (12 in each group). Plasma meperidine levels were assayed by gas chromatography. Complete motor block was achieved in all Group 2 patients, but was incomplete in seven of Group 1 (P less than 0.05). The onset of both motor and sensory blocks was shorter (P less than 0.01) in Group 2 and the duration was longer (P less than 0.05). Coadministration of prilocaine modifies meperidine pharmacokinetic behaviour. The area under curve was 48% greater (P less than 0.01) and Cmax was higher in Group 2 than in Group 1, 145.8 +/- 42.2 vs 107 +/- 20.5 ng.ml-1 (P less than 0.001). No evidence of respiratory depression was noted in any of the patients. Despite the increase in plasma meperidine concentrations, no side effects were observed. The plasma concentrations remained at one third to one sixth the levels reported to induce a respiratory depression. It is concluded that the addition of prilocaine to meperidine improves motor and sensory block during surgery and alters meperidine kinetics without producing major side effects.