Morphine is an effective analgesic for cancer pain. Pain relief did not differ between Mm/r and MIR. Modified release versions of morphine were effective for 12- or 24-hour dosing depending on the formulation. Daily doses in studies ranged from 25 mg to 2000 mg with an average of between 100 mg and 250 mg. Dose titration was undertaken with both instant release and modified release products. A small number of participants did not achieve adequate analgesia with morphine . Adverse events were common, predictable, and approximately 6% of participants discontinued treatment with morphine because of intolerable adverse events.
24 hourly oral morphine (mg) fentanyl patch (mcg/hour) 30 12 60 25 120 50 180 75 240 100
Opioids are a class of compounds that elicit analgesic (pain killing) effects in humans and animals by binding to the µ-opioid receptor within the central nervous system . The following table lists opioid and non-opioid analgesic drugs and their relative potencies . Values for the potencies represent opioids taken orally unless another route of administration is provided. As such, their bioavailabilities differ, and they may be more potent when taken intravenously . Methadone is different from most opioids considering its potency can vary depending on how long it is taken. Acute use, 1–3 days, yields a potency about × stronger than that of morphine and chronic use (7 days+) yields a potency about to 5× that of morphine due to methadone being stored in fat tissue, thus giving higher serum levels with longer use. [ citation needed ] Similarly, the effect of tramadol increases after consecutive dosing due to the accumulation of its active metabolite and an increase of the oral bioavailability in chronic use, this effect becomes less significant again with even longer use as tolerance develops. [ citation needed ]