What is the recommended dose of mefenamic acid for a 14-year-old or older patient with impaired renal function or at risk of gastrointestinal bleeding?

Mefenamic Acid Dosing in Adolescents and High-Risk Patients

Standard Dosing Recommendation

For patients 14 years or older, the standard dose of mefenamic acid is 500 mg three times daily (every 8 hours) for a maximum of 7 days, regardless of renal function or bleeding risk—however, mefenamic acid should be avoided entirely in patients with impaired renal function (creatinine clearance <30 mL/min) or those at significant risk of gastrointestinal bleeding. 1, 2

Critical Contraindications and When to Avoid Mefenamic Acid

Renal Impairment

• Mefenamic acid is contraindicated in moderate to severe renal impairment (CrCl <30 mL/min) and should be used with extreme caution even in mild renal dysfunction, as NSAIDs can precipitate acute kidney injury and worsen existing renal disease 3
• No dose adjustment guidelines exist for mefenamic acid in renal impairment—the drug should simply be avoided and alternative analgesics selected 3
• Calculate creatinine clearance using the Cockcroft-Gault equation before initiating therapy in any patient with suspected renal compromise 4

Gastrointestinal Bleeding Risk

• Patients at high risk for GI bleeding (age ≥65 years, history of peptic ulcer disease, prior GI bleeding, concurrent anticoagulant use, antiplatelet therapy, SSRIs, or corticosteroids) should not receive mefenamic acid without mandatory gastroprotection with a proton pump inhibitor 3, 5
• The risk of GI bleeding is dose-dependent across all NSAIDs, and mefenamic acid carries similar risks to other non-selective NSAIDs 3
• If the patient is taking anticoagulants (warfarin, DOACs, heparin), mefenamic acid should be avoided entirely, as the combination increases bleeding risk 3-6 fold 3, 5

Dosing Protocol for Appropriate Candidates

Standard Regimen

• 500 mg orally three times daily (every 8 hours) for 5-7 days maximum 1, 6, 2
• The medication should be taken with food to minimize gastrointestinal side effects 1
• Treatment duration should not exceed 7 days due to cumulative toxicity risks 1, 2

Alternative Dosing

• A 250 mg dose three times daily may be considered for initial therapy in patients with concerns about tolerability, though efficacy data are limited at this lower dose 1
• For dysmenorrhea specifically, 500 mg every 8 hours for a maximum of 3 days during menstruation has proven effective 2

Monitoring Requirements

Baseline Assessment

• Obtain baseline renal function (BUN, creatinine, calculate CrCl), liver function tests, complete blood count, and assess for occult GI bleeding risk factors before initiating therapy 3, 5
• Document blood pressure, as NSAIDs can exacerbate hypertension 3

During Treatment

• For short-term use (≤7 days), no routine monitoring is required in healthy patients 1
• Discontinue immediately if any signs of GI bleeding (melena, hematemesis, severe abdominal pain), acute kidney injury (oliguria, edema, rising creatinine), or hepatotoxicity (jaundice, right upper quadrant pain) develop 3, 5

Special Populations

Adolescents (14-18 years)

• Use the standard adult dose of 500 mg three times daily 1, 2
• Adolescents generally tolerate mefenamic acid well, with no dose adjustment needed based on age alone 1

Elderly Patients (≥65 years)

• Mefenamic acid should be avoided in elderly patients due to significantly increased risks of GI bleeding, renal toxicity, and cardiovascular events 3, 5
• If absolutely necessary, use the lowest effective dose (250 mg three times daily) with mandatory PPI co-therapy and close monitoring 3

Cardiovascular Disease

• Use mefenamic acid with extreme caution in patients with pre-existing cardiovascular disease, heart failure, or hypertension, as NSAIDs increase risk of myocardial infarction, stroke, and fluid retention 3, 5
• Consider alternative analgesics such as acetaminophen (up to 3000 mg daily) in high-risk cardiac patients 3

Safer Alternatives in High-Risk Patients

For Renal Impairment

• Acetaminophen 500-1000 mg every 6-8 hours (maximum 3000 mg/day) is the safest analgesic option 3
• Topical NSAIDs (diclofenac gel) minimize systemic exposure while providing localized pain relief 3
• Opioid analgesics may be necessary for severe pain, with appropriate dose adjustments for renal function 5

For GI Bleeding Risk

• Acetaminophen remains first-line 3
• If NSAID therapy is essential, consider celecoxib (a COX-2 selective inhibitor) with PPI co-therapy, as it carries lower GI bleeding risk than non-selective NSAIDs like mefenamic acid 3
• Topical NSAIDs avoid systemic GI toxicity 3

Critical Pitfalls to Avoid

• Never combine mefenamic acid with other NSAIDs, as many patients inadvertently use over-the-counter ibuprofen or naproxen concurrently, dramatically increasing toxicity risk 3
• Do not exceed 7 days of continuous therapy without reassessing the need for continued NSAID use 1, 2
• Never prescribe mefenamic acid to patients on anticoagulation without first considering the 3-6 fold increased bleeding risk and exploring safer alternatives 3, 5
• Avoid in third trimester pregnancy due to risk of premature closure of ductus arteriosus 5
• Do not use mefenamic acid in patients with active peptic ulcer disease, severe heart failure, or liver failure 5