[Weak opioids. Meta-analysis for the therapy of chronic pain]

Weak opioids have a maximal dose (ceiling effect), and their distribution and prescription is not controlled by German narcotic laws. In a literature search (Medline 1963-1995) and our own literature database on pain treatment, 58 publications were identified. These reported about 130 comparisons of weak opioids with different analgesics. The statistical parameters of a meta-analysis were not calculated, due to great differences of the study design and the examined drugs. The results of this literature analysis demonstrate the analgesic efficacy of weak opioids in chronic pain. Non-opioid analgesics and strong opioids, however, have greater potency. These results are based mainly on single-dose studies; controlled long-term studies are required. Especially the risk of serious complications involving the gastrointestinal tract, kidney and blood cells during long-term treatment with non-opioid analgesics or weak opioids needs to be evaluated. In addition, the combination of non-opioid analgesics and weak opioids versus the combination of nonopioid analgesics and placebo or low-dose strong opioids has to be investigated. The results of this literature analysis support the use of weak opioids in the symptomatic treatment of chronic pain, though the evidence of the available literature is limited. It can be recommended to prescribe weak opioids according to the WHO ladder in combination with non-opioid analgesics. If this combination provides no adequate analgesic efficacy, however, the use of strong opioids must not be delayed.