Chapter 25: Analgesics & Pain Management Drugs

A significant portion of the chapter is dedicated to nonopioid analgesics, differentiating between Nonsteroidal Antiinflammatory Drugs (NSAIDs) like aspirin, ibuprofen, and COX-2 inhibitors, which reduce pain and inflammation by inhibiting cyclooxygenase enzymes, and acetaminophen, a para-aminophenol derivative that offers analgesic and antipyretic benefits without anti-inflammatory properties. The narrative highlights critical safety concerns, such as the risk of Reye syndrome in children taking aspirin and the potential for severe hepatotoxicity with acetaminophen overdose, for which acetylcysteine is the specific antidote. The discussion then transitions to opioid analgesics used for moderate to severe pain, using morphine as the prototype agonist that binds to mu-receptors in the central nervous system. Key physiological responses to opioids, including respiratory depression, orthostatic hypotension, urinary retention, and constipation, are examined in detail along with pharmacokinetics and administration methods like Patient-Controlled Analgesia (PCA) and transdermal patches (fentanyl). The chapter also covers opioid antagonists like naloxone, which are essential for reversing respiratory depression caused by overdoses, and opioid agonist-antagonists like nalbuphine and pentazocine. Furthermore, the text addresses the management of vascular headaches, distinguishing between migraine and cluster headaches, and detailing the mechanism of selective serotonin receptor agonists (triptans) like sumatriptan. Finally, special considerations for pain management across the lifespan are reviewed, including the World Health Organization analgesic ladder for cancer pain, the use of adjuvant therapies like anticonvulsants for neuropathic pain, and safety modifications for pediatric and geriatric populations.