M-6-G is a potent opioid agonist and M-3-G a mild opioid antagonist. Both are poorly excreted in patients with renal failure. However, the metabolism of morphine was rapid when compared to the transfer of metabolites through the blood-brain barrier, which appears to be the limiting process. Because poor analgesia due to M-3-G's effect may occur in some patients after 1 or 2 days, a switch to other molecules should be considered.

Can immediate opioid requirements in the post-anaesthesia care unit be used to determine analgesic requirements on the wardg.The aim of this prospective study was to evaluate the efficacy of two dosage regimens of (ira) morphine calculated from an initial (iv) titrated dose in the early postoperative period. Seventy ASA 1-111 patients who underwent general anaesthesia (GA) (n = 58), regional anaesthesia (RA) (n = 10) or GA + RA (n = 2) for orthopaedic (n = 54), urological (n = 11) or abdominal surgery (n = 5) received iv titrated morphine in the post-anaesthesia care unit (PACU). Titration consisted of 3 mg morphine iv every ten minutes until patients had a visual analogue pain scale (VAS) <3, without marked sedation. Seventeen patients did not complain at all or had good analgesiawith an initial iv dose _<6 mg of morphine followed by paracetamol only. Patients who needed more than 6 mg iv morphine were randomly assigned to a "high-dose" or a "low-dose" group and received a systematic im morphine regimen calculated from the initial titrated dose. Pain was assessed by VAS before each im injection and the next morning. One patient had respiratory depression and one marked sedation in the PACU These patients were excluded from the rest of the study. Only 16patients had a VAS >3 at least once during the study period and only three needed rescue analgesia which was avail-

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