What is the first‑line analgesic regimen and dosing for an adult with acute flank pain due to nephrolithiasis, assuming no contraindications?

First-Line Analgesic for Acute Nephrolithiasis Flank Pain

NSAIDs—specifically diclofenac, ibuprofen, or metamizole—are the first-line analgesic for acute renal colic, with opioids reserved only as second-line therapy when NSAIDs are contraindicated or ineffective. 1, 2

Recommended NSAID Regimens

Primary Options

• Diclofenac 50-75 mg intramuscularly is the most extensively studied NSAID for renal colic 3, 4
• Ibuprofen 400 mg orally every 6-8 hours (maximum 3200 mg/day) 1, 2
• Ketorolac 15-30 mg intravenously for short-term use (maximum 5 days) 1, 2
• Metamizole (where available) is also recommended as first-line 1, 4

Route of Administration

• Intravenous administration is preferred for acute presentations (65% of urologists use IV route) 4
• Intramuscular diclofenac is highly effective based on trial data 3, 5

Why NSAIDs Are Superior to Opioids

NSAIDs provide equivalent or superior pain control compared to opioids while causing significantly fewer adverse effects. 1, 2, 6, 5

Evidence of Superiority

• NSAIDs reduce the need for rescue medication by 25% compared to placebo (RR 0.35,95% CI 0.20-0.60) 6
• NSAIDs are 2.28 times more effective than placebo in achieving 50% pain reduction within the first hour 6
• Patients receiving NSAIDs have 65% less vomiting compared to opioids, particularly pethidine (RR 0.35,95% CI 0.23-0.53) 5
• NSAIDs decrease the need for additional analgesia compared to opioids 1, 6

Second-Line: Opioid Therapy

Opioids should only be used when NSAIDs are contraindicated or provide inadequate pain control. 2, 3

Preferred Opioids

• Morphine 5-10 mg intravenously or subcutaneously 3
• Hydromorphine, pentazocine, or tramadol are acceptable alternatives 2
• Avoid pethidine (meperidine) due to the highest rate of adverse effects among opioids 2, 5

Combination Therapy

• Adding morphine to NSAIDs provides additional benefit in approximately 10% of patients when NSAIDs alone are insufficient 3

Critical Contraindications and Cautions for NSAIDs

NSAIDs must be used with extreme caution or avoided entirely in specific high-risk populations. 1, 2

Absolute or Relative Contraindications

• Renal impairment: Patients with chronic kidney disease, dehydration, solitary kidney, or concurrent nephrotoxic drugs 1, 2
• Cardiovascular disease: History of heart failure, hypertension, or cardiovascular risk factors 1
• Gastrointestinal risk: Age >60 years, peptic ulcer disease history, or significant alcohol use (≥2 drinks/day) 1
• Bleeding disorders: Thrombocytopenia or concurrent anticoagulation 1
• Pregnancy: NSAIDs should never be used during pregnancy 3

For High-Risk Patients

• Use opioids as first-line in patients with the above contraindications 2
• Fentanyl and buprenorphine are the safest opioid choices for chronic kidney disease stages 4-5 2

Monitoring Requirements Before and During NSAID Use

Baseline laboratory assessment is mandatory before initiating NSAID therapy. 2

Required Baseline Tests

• Blood pressure measurement 2
• BUN and creatinine 2
• Liver function studies 2
• Complete blood count 2
• Fecal occult blood test 2

Ongoing Monitoring

• Repeat all baseline tests every 3 months during continued NSAID use 2

Discontinuation Criteria

• Stop NSAIDs immediately if: 1, 2
  • BUN or creatinine doubles from baseline
  • Hypertension develops or worsens
  • Liver function studies increase above normal limits
  • Peptic ulcer or gastrointestinal hemorrhage occurs

Ineffective or Not Recommended Therapies

Antispasmodics

• Adding antispasmodics to NSAIDs provides no additional benefit (RR 1.00,95% CI 0.89-1.13) 6
• NSAIDs alone are significantly more effective than antispasmodics for pain control (MD -12.97,95% CI -21.80 to -4.14) 6
• Scopolamine added to morphine showed no additional efficacy 3

Indomethacin

• Indomethacin is less effective than other NSAIDs (RR 1.27,95% CI 1.01-1.60) and should not be the preferred NSAID choice 6

Common Pitfalls to Avoid

• Do not use pethidine (meperidine) as it has the highest vomiting rate (20% vs 6% with NSAIDs) and inferior efficacy 2, 3, 5
• Do not delay emergency decompression if fever (suggesting sepsis) or anuria is present—these require urgent urological intervention, not just analgesia 1
• Do not use NSAIDs long-term without monitoring in patients with borderline renal function 2
• Do not combine two NSAIDs or two sustained-release opioids simultaneously 1