Is it safe to prescribe naproxen (nonsteroidal anti-inflammatory drug) 500 mg to a 15-year-old patient weighing 121 pounds?

Naproxen 500 mg Dosing in a 15-Year-Old Weighing 121 Pounds

Yes, naproxen 500 mg can be prescribed to this 15-year-old patient, as the FDA-approved pediatric dosing for patients over 2 years is 5 mg/kg per dose (not exceeding 15 mg/kg/day total), and this patient's weight of 121 pounds (55 kg) would allow for a maximum single dose of 275 mg using strict weight-based calculations—however, the FDA label indicates that pediatric patients over 2 years tolerate single doses of 2.5 to 5 mg/kg well, and clinical practice commonly uses adult dosing (500 mg) in adolescents of this size, though starting with a lower dose (250-375 mg) would be more conservative. 1

Weight-Based Dosing Calculations

• This patient weighs 121 pounds, which equals approximately 55 kg 1
• The FDA-approved pediatric dosing is 2.5 to 5 mg/kg per dose, with total daily dose not exceeding 15 mg/kg/day 1
• Using 5 mg/kg: 55 kg × 5 mg/kg = 275 mg per dose (maximum conservative dose) 1
• Maximum daily dose: 55 kg × 15 mg/kg = 825 mg/day 1

Clinical Considerations for Adolescents

• The FDA label states that "single doses of 2.5 to 5 mg/kg are well tolerated in pediatric patients over 2 years of age" 1
• Naproxen 500 mg represents approximately 9 mg/kg for this patient (500 mg ÷ 55 kg), which exceeds the strict 5 mg/kg guideline but remains well below the 15 mg/kg/day maximum if given once daily 1
• Pharmacokinetic studies in pediatric patients aged 5-16 years showed that plasma naproxen levels following a 5 mg/kg dose were similar to those in adults receiving 500 mg 1

Practical Prescribing Approach

Start with a lower dose of 250-375 mg twice daily rather than 500 mg, which provides adequate analgesia while staying within conservative weight-based parameters. 1

• If 500 mg is deemed necessary for adequate pain control, it can be given once or twice daily (not exceeding 1000 mg/day total for this patient weight) 1
• The elimination half-life of 12-17 hours supports twice-daily dosing for sustained effect 1
• Steady-state levels are reached in 4-5 days 1

Safety Monitoring Requirements

• Cardiovascular risk: NSAIDs including naproxen carry increased risk of serious cardiovascular thrombotic events, myocardial infarction, and stroke, though naproxen may have a more favorable cardiovascular profile compared to other NSAIDs 2
• Gastrointestinal risk: Monitor for gastric upset, ulceration, or bleeding; adolescents have lower baseline risk than elderly patients but risk increases with dose and duration 2
• Renal monitoring: Check baseline BUN and creatinine; naproxen is substantially excreted by the kidney and metabolites may accumulate with renal impairment 1
• Avoid in patients with compromised fluid status or concurrent nephrotoxic medications 2

Key Contraindications and Precautions

• Do not use if the patient has known hypersensitivity to naproxen or other NSAIDs 1
• Contraindicated in perioperative pain setting of coronary artery bypass graft (CABG) surgery 2
• Use with extreme caution if patient has cardiovascular disease, heart failure, hypertension, or fluid retention 2, 1
• Avoid in patients with active peptic ulcer disease or history of gastrointestinal bleeding 2

Duration and Follow-Up

• Use the lowest effective dose for the shortest duration necessary 2
• If using for more than short-term treatment (>1-2 weeks), consider monitoring CBC, liver function, and renal function every 3 months 2
• Educate patient and family about warning signs: severe abdominal pain, black/tarry stools, chest pain, shortness of breath, weakness, or slurred speech 2