Despite increasing understanding of the endogenous nociceptive and antinociceptive system, l two classes of compounds continue to dominate clinical analgesia: cyclooxygenase inhibitors (nonsteroidal antiinflammatory agents, eg, aspirin, paracetamol, ibuprofen), which act mainly peripherally by inhibiting prostaglandin synthesis, and opiates (eg, morphine, codeine), which act on specific central nervous system receptors. However, ...