"One randomized dose-response study (
43) allowed patients free access to IVPCA after epidural administration of saline or 1 of 4 doses of morphine (1.25, 2.5, 3.75, or 5 mg). Quality of analgesia improved as the dose of epidural morphine increased to 3.75 mg. Beyond that, there was no difference in analgesic effect as measured by IVPCA use. All women given epidural morphine experienced pruritus, but there was no correlation with the dose of epidural morphine. Analgesia lasted for 1826 h. "
http://www.anesthesia-analgesia.org/cgi/content/full/101/5S_Suppl/S62
Spinals:
"A meta-analysis (
33) demonstrated excellent efficacy of morphine doses of 0.1 to 0.2 mg but no additional pain relief with doses >0.2 mg. Median time to first request for supplemental analgesics in that study was 27 h. In contrast, doses smaller than 0.1 mg had little effect on pain relief. "