Efficacy and Safety of Opioid Analgesia in Acute Abdominal Presentations: A Systematic Review

Acute abdominal pain is a common emergency department presentation and is often associated with diagnostic uncertainty. Historically, opioid analgesia was used cautiously because of concern that it could alter physical examination findings and interfere with diagnostic accuracy. Non-opioid and opioid-sparing strategies are increasingly used for pain management. This systematic review evaluates the efficacy and safety of analgesic strategies for acute, non-traumatic abdominal pain, with attention to pain relief, adverse effects, rescue analgesia, and diagnostic accuracy. PubMed, Embase, and the Cochrane Central Register of Controlled Trials were searched for randomized comparative trials of opioid-containing treatment versus non-opioid, opioid-sparing, or placebo strategies. Eligible studies included adults aged 18 years or older with acute abdominal pain or an acute intra-abdominal cause of pain; studies limited to renal or ureteric colic were excluded. Of the 316 records identified, 45 duplicates were removed, 271 records were screened, 26 reports underwent full-text assessment, and 16 randomized trials were included. Across the included trials, opioids provided effective short-term analgesia but were not consistently superior to alternatives. Hydromorphone produced greater pain improvement than intravenous lidocaine at 90 minutes (between-group difference = 1.2 points, 95% confidence interval (CI) = 0.3-2.2) with less rescue analgesia. In acute pancreatitis, median Visual Analog Scale (VAS) reductions at 30 minutes were 45.5 (95% CI = 30-54) with tramadol, 41.5 (95% CI = 34-50) with paracetamol, and 40.5 (95% CI = 30-47) with dexketoprofen, with no statistically significant between-group difference. An erector spinae plane block produced lower pain scores and reduced rescue fentanyl compared with intravenous tramadol. In biliary colic, mean pain relief at 30 minutes was 3.8 (95% CI = 2.4-5.2) with ketorolac and 3.9 (95% CI = 2.4-5.3) with meperidine, with no statistically significant between-group difference. Butorphanol provided greater early pain relief than ketorolac at 15 minutes but not at 30 minutes. Low-dose morphine plus paracetamol did not significantly differ from standard-dose morphine, and intravenous lidocaine and morphine did not significantly differ at the primary 60-minute endpoint. Several placebo-controlled trials assessed diagnostic accuracy using different definitions and patient populations. In one trial, diagnostic accuracy was 86% with morphine and 85% with placebo (difference 1 percentage point, 95% CI = -11 to 12). This imprecise estimate does not rule out a clinically important difference, and the available trials do not establish whether opioids affect diagnostic accuracy across acute abdominal presentations. Some studies identified changes in tenderness, rigidity, or localization after analgesia, but these were not consistently associated with diagnostic error or adverse management outcomes. Adverse effects were generally short-term and included nausea, vomiting, dizziness, and sedation, although most trials were not large enough or followed long enough to reliably evaluate uncommon serious adverse events. Overall, the evidence supports an individualized approach to analgesia. Opioids remain effective when clinically indicated, but are not consistently superior to non-opioid or opioid-sparing alternatives, and analgesia should not be routinely delayed solely because of concern for diagnostic interference.