A look inside the association codeine-paracetamol: clinical pharmacology supports analgesic efficacy.

Acute and chronic pain often requires a multimodal approach. Combination therapy reduces the number of individual daily administrations and improves patient's compliance with the prescribed analgesic treatment. Despite the association codeine/paracetamol is one of the most widely used central analgesic, the exact mechanism of action, particularly of paracetamol, is still object of pharmacological research. Recent findings showed that paracetamol may act through cerebral cyclo-oxygenase, descending opioidergic inhibitory pathways, serotonin pathway, and the endocannabinoid system; while codeine activity seems to related not only to its conversion to morphine, as previously known, but also by itself and through its metabolites, such as norcodeine (NORC) and codeine-6-glucuronide (C-6-G). The addition of codeine to paracetamol significantly improves the analgesic action and reduces the number needed to treat (NNT) from 5 to 2.3-3.1. Recent warnings about the risk of its metabolism related to CYP450 and its genetic variability in general population should be mainly considered when the association is used in paediatric patients undergoing tonsillectomy and/or adenoidectomy procedures for obstructive sleep apnoea syndrome (OSAS). In adults, the association codeine/paracetamol has been shown to be effective and safe in different settings: acute pain, trauma patients, and chronic nociceptive pain.