English:
Weak opioids. Codeine is the most commonly used drug in this class. Codeine Th is, in fact, a prodrug of morphine and is dependent on conversion to the active analgesic in the gut. About 8-25% of the population an are so-called 'slow con for whom codeine has little or no analgesic effect. Codeine (60 mg) alone has an NNT of 16.7 but when combined with paracetamol 1000 mg. this falls to 2.2 Codeine causes typical opioid side effects (see below). with constipation being the most troublesome. Tramadol and tapentadol Tramadol is regarded as an opioid analgesic but. while it does exhibit activity on the opioid mu receptor, this alone does not account for its analgesic effects. Tramadol inhibits the re-uptake of both noradrenaline and serotonin (5HT) and blockade of these mechanisms will partially reverse tramadol-induced analgesia. These actions may make tramadol more effective for neuropathic pain than pure opioids. The weak effect on mu receptors means that tramadol causes less respiratory depression than. for example, morphine. Side-effects are common. however, and include nausea and vomiting, dizziness and drowsiness. The effects on serotonin mean that using tramadol may have serious interactions with antidepressants, in particular the serotonin re uptake inhibitors such as fluoxetine. Tapentadol has recently been licensed in the USA and is expected to be available in Europe in 2010. It is similar to tramadol except that it does not have an effect on serotonin re-uptake. RCTs have shown that it can offer comparable anal. gesia to opioids such as oxycodone in both acute and chronic pain models but with less than half the incidence of gastroin- testinal side-effects such as nausea and constipation.