Pharmacological Pain Management

Core Concepts

Classes of analgesic medications

• Nonopioid analgesics. Acetaminophen is an analgesic and antipyretic that acts mainly in the central nervous system; it has no meaningful anti-inflammatory effect. NSAIDs reduce prostaglandin production — chemicals that sensitize pain receptors and drive inflammation — so they relieve pain and inflammation. Both are common first-line options for mild to moderate pain and are often combined with each other or with opioids.
• Opioid analgesics. These bind opioid receptors in the brain and spinal cord and are among the most powerful options for moderate to severe acute pain. Classic side effects: constipation, nausea and vomiting, sedation, and respiratory depression. With ongoing use, tolerance and physical dependence can develop — see Substance Use Disorder for how these differ from addiction.
• Adjuvant analgesics. Drugs developed for other purposes that also relieve certain pain — tricyclic antidepressants and SNRIs for neuropathic pain, certain antiseizure medications for nerve pain, and local anesthetics. They are especially useful when ordinary analgesics only partly control the pain.

Matching the drug to the pain

Nociceptive pain (from tissue injury — aching, throbbing, sharp) generally responds to NSAIDs, acetaminophen, and opioids. Neuropathic pain (from nervous system damage — burning, shooting, electric-like) responds less reliably to opioids; adjuvants are often emphasized. Asking "what kind of pain is this?" is a real clinical step — the answer changes which drug is likely to help. First-line choices change as guidelines are updated, so verify current recommendations rather than memorizing an old rule.

Routes and delivery systems

Route affects onset and duration. Oral is convenient but subject to first-pass metabolism — the liver processes the drug before it reaches general circulation. IV acts fastest and is used for severe acute pain. Subcutaneous and intramuscular routes fall in between. Transdermal patches release drug slowly and steadily — suited to stable chronic pain, never to new or rapidly changing pain. Topical preparations treat localized pain. Epidural or intrathecal delivery places drug near the spinal cord for powerful effect at small doses. Patient-controlled analgesia (PCA) pumps let the patient deliver a small preset dose within a "lockout" period — patient control with built-in limits.

Dosing strategies

• Scheduled (around-the-clock) dosing keeps a steady drug level for constant pain — usually more effective than waiting for pain to return.
• PRN (as-needed) dosing covers breakthrough pain or variable pain.
• Equianalgesia compares opioids for roughly equivalent relief — essential when switching opioids, because equal milligrams of different opioids are not equal strength.
• Multimodal analgesia deliberately combines classes (scheduled nonopioid plus small-dose opioid for breakthrough) for better relief with lower doses and fewer side effects.
• The WHO analgesic ladder — a stepwise framework originally developed for cancer pain (nonopioids → weak opioids → strong opioids) — is a classic teaching model, though modern practice frequently individualizes rather than following strict steps.

Safety, monitoring, and the nurse's role

The nurse assesses pain before giving the drug, then reassesses after enough time for the route's expected peak effect. With opioids, monitoring includes sedation and respiratory status, since sedation can precede respiratory depression. Constipation is so common with opioids that prevention is routinely part of care. The nurse checks allergy history, watches for interactions, documents the response, and teaches the patient what to report. Controlled substances are governed by regulated schedules, secure storage, and documentation requirements that vary by jurisdiction and facility — and what a nurse may initiate or titrate depends on scope of practice and institutional policy. This guide gives no doses: always use current order sets and references at the point of care.

Common Confusions