Pharmacologic Pain Management and Analgesic Safety
Multimodal analgesia
Combine agents with different mechanisms so each dose can be lower and safer. Acetaminophen is capped at 4 g/day in healthy adults (often 3 g with hepatic risk, alcohol use, or frailty) - count every combination product. NSAIDs carry GI bleeding, acute kidney injury, platelet, and cardiovascular risk; avoid in renal impairment, anticoagulation, post-CABG, and third trimester of pregnancy.
Opioids act at mu receptors. Titrate to the patient's report plus sedation score and respiratory rate. Sedation precedes respiratory depression - monitor with a tool such as POSS and never rely on pupil size. Constipation does not develop tolerance, so prescribe a bowel regimen; nausea and sedation usually do. Naloxone is titrated, may need repeat dosing, and its duration can be shorter than the opioid's.
Conversions and safety
When switching opioids, calculate the equianalgesic dose, then reduce by 25–50% for incomplete cross-tolerance and reassess. Avoid meperidine (normeperidine seizures). Codeine and tramadol depend on CYP2D6 activity - avoid in children after tonsillectomy and in breastfeeding mothers. Adjuvants include gabepentinoids (renal dosing, sedation), TCAs (anticholinergic and cardiac effects), SNRIs, ketamine, lidocaine infusions, corticosteroids, and topical agents.
Traps
A request for a higher dose is not automatically drug-seeking; untreated pain produces the same behavior (pseudoaddiction). Do not delay analgesia in sickle cell vaso-occlusive crisis. Never stop opioids abruptly in a tolerant patient - taper to avoid withdrawal.
Rule of thumb: calculate the equianalgesic dose, cut it 25–50%, give it, and reassess - never convert and give the full calculated dose.