What is the best initial pain reliever to administer to a patient in pain?

Initial Pain Management: Evidence-Based Approach

For a patient presenting with pain, start with acetaminophen (paracetamol) 500-1000 mg orally as the first-line agent for mild pain, or combine it with ibuprofen 400 mg for moderate pain, escalating to oral morphine 20-40 mg for severe pain according to the WHO analgesic ladder. 1, 2

Pain Severity Assessment and Treatment Algorithm

Mild Pain (NRS 1-4)

• Begin with acetaminophen 500-1000 mg orally every 4-6 hours (maximum 4000-6000 mg/day), which provides effective analgesia with onset in 15-30 minutes and superior safety compared to NSAIDs 1, 3
• Alternatively, use ibuprofen 400 mg orally every 4-6 hours (maximum 2400 mg/day) if no gastrointestinal, renal, or cardiovascular contraindications exist 1, 4
• Acetaminophen is preferred as first-line because it lacks the gastrointestinal bleeding, renal toxicity, and cardiovascular risks associated with NSAIDs 5, 6

Moderate Pain (NRS 5-7)

• Combine acetaminophen 1000 mg with ibuprofen 400 mg every 4-6 hours, as this multimodal approach provides superior analgesia to either agent alone 1, 2
• If inadequate relief, add a weak opioid: codeine 30-60 mg, tramadol 50-100 mg, or dihydrocodeine 60-120 mg combined with the non-opioid analgesic 1
• As an alternative, consider low-dose strong opioids (morphine 10-20 mg orally) instead of weak opioids, which may provide more predictable analgesia 1, 2

Severe Pain (NRS 8-10)

• Initiate oral morphine 20-40 mg immediately for opioid-naïve patients, as this is the first-choice strong opioid with no upper dose limit 1, 2
• For urgent relief or inability to take oral medications, administer parenteral morphine 5-10 mg IV or subcutaneous, recognizing the oral-to-parenteral potency ratio is 1:2 to 1:3 1, 2
• Continue acetaminophen 1000 mg every 4-6 hours as background analgesia, since it remains effective for all pain intensities when combined with opioids 1, 2
• Alternative strong opioids include oxycodone 20 mg orally (1.5-2× morphine potency) or hydromorphone 8 mg orally (7.5× morphine potency) 1, 2

Critical Dosing Principles

Scheduling and Rescue Dosing

• Administer analgesics on a fixed schedule ("around-the-clock") rather than "as needed" for baseline pain control 1, 2
• Provide immediate-release morphine every 4 hours with rescue doses (10-15% of total daily dose) available up to hourly for breakthrough pain 1, 2
• If more than 4 breakthrough doses are needed per 24 hours, increase the baseline opioid dose accordingly 1

Route Selection

• Oral administration is the preferred route even for severe pain, as it provides reliable absorption and easier titration 1, 2
• Reserve parenteral routes (IV/subcutaneous) for patients requiring urgent relief, unable to swallow, or with poor oral tolerance 1, 2
• Avoid intramuscular injections, which are painful and offer no pharmacokinetic advantage 1

Essential Prophylaxis

Mandatory Co-Prescriptions with Opioids

• Prescribe laxatives routinely for all patients receiving opioids to prevent constipation, as this occurs in nearly all patients 1, 2
• Provide antiemetics (metoclopramide or antidopaminergic agents) for opioid-induced nausea/vomiting 1, 2

NSAID Precautions

• Add gastroprotection (proton pump inhibitor) when NSAIDs are used for more than a few days 1
• Exercise caution with NSAIDs in patients at risk for bleeding, renal impairment, or cardiovascular disease 1, 4

Special Populations

Renal Impairment

• Use all opioids with caution at reduced doses and frequency in renal impairment 1, 2
• For advanced kidney disease (eGFR <30 mL/min), fentanyl and buprenorphine are the safest opioid choices as they lack active metabolites that accumulate 1, 2

Older Adults

• No routine dose reduction is required for acetaminophen in older patients; maintain standard dosing up to 4000 mg/day 5
• Consider individual factors such as frailty, polypharmacy, and comorbidities when selecting NSAIDs or opioids 5

Common Pitfalls to Avoid

• Do not delay strong opioids for severe pain—the WHO ladder allows starting at step 3 when pain severity warrants it 1, 2
• Do not use weak opioids (codeine, tramadol) for severe pain, as they have ceiling effects and unpredictable efficacy 2, 6
• Do not prescribe two sustained-release opioid formulations together; use one long-acting formulation with immediate-release for breakthrough 2
• Do not initiate transdermal fentanyl for acute pain or rapid titration—it is only appropriate once pain is controlled with other opioids and requirements are stable 1, 2
• Do not exceed acetaminophen 4000 mg/day to avoid hepatotoxicity risk 1, 3, 5
• Do not exceed ibuprofen 2400 mg/day (400 mg every 4-6 hours), as higher doses increase adverse effects without improving efficacy 4, 6