What is the appropriate acetaminophen (Tylenol) dose for a 17‑year‑old female weighing about 55 kg?

Acetaminophen Dosing for a 17-Year-Old Female

For a 17-year-old female weighing approximately 55 kg, the appropriate acetaminophen dose is 650–1000 mg every 4–6 hours, with a maximum of 4000 mg per 24 hours, though a more conservative limit of 3000 mg daily is increasingly recommended for safety. 1, 2, 3

Standard Dosing Parameters

• Single dose: 650–1000 mg (maximum 1000 mg per dose) 1, 3
• Dosing interval: Every 4–6 hours as needed 1, 2
• Maximum daily dose: 4000 mg per 24 hours (FDA-approved maximum) 1, 2, 3
• Conservative daily maximum: 3000 mg per 24 hours for chronic or repeated use to minimize hepatotoxicity risk 1, 2

Critical Safety Counseling Required

You must explicitly counsel this patient to avoid all other acetaminophen-containing products, including: 1, 2

• Over-the-counter cold and flu remedies
• Sleep aids (many contain acetaminophen)
• Combination pain relievers
• Any prescription opioid-acetaminophen combinations

This is the most common cause of unintentional acetaminophen overdose in clinical practice. 2

When to Use the Conservative 3000 mg Limit

If this patient will be using acetaminophen for more than 7–10 days, limit the total daily dose to 3000 mg rather than the FDA maximum of 4000 mg. 1, 2 This recommendation is based on:

• Evidence that therapeutic doses of 4 g/day for 14 days can cause ALT elevations >3× normal in 31–41% of healthy adults 1
• Repeated supratherapeutic ingestions (doses just above therapeutic range) carry worse prognosis than acute single overdoses, accounting for approximately 30% of acetaminophen overdose admissions 1, 2

Practical Dosing Algorithm

For acute pain or fever (≤7 days):

• Start with 650–1000 mg every 4–6 hours 1
• Maximum 4000 mg per 24 hours 3
• Track all doses carefully to avoid exceeding limits 4

For chronic or repeated use (>7–10 days):

• Use 650–1000 mg every 6 hours 2
• Maximum 3000 mg per 24 hours 1, 2
• If pain control is inadequate, add adjuvant therapies (NSAIDs, topical agents) rather than increasing acetaminophen dose 2

Red Flags Requiring Dose Reduction

Do not use standard dosing if this patient has: 1, 2, 3

• Chronic liver disease or cirrhosis (limit to 2000–3000 mg daily)
• Chronic alcohol use (hepatotoxicity can occur at doses ≤4000 mg)
• Concurrent use of other hepatotoxic medications

Common Prescribing Pitfalls to Avoid

• Failing to account for acetaminophen in combination products: If prescribing opioid-acetaminophen combinations, the acetaminophen content must count toward the daily maximum 2
• Not providing a dosing record: Recommend the patient keep a written log of all doses and times to prevent accidental overdose 4
• Assuming the FDA maximum is safe for chronic use: The 4000 mg daily limit is increasingly recognized as too high for extended use 1, 2, 5

Warning Signs of Toxicity

Instruct the patient to seek immediate medical attention if she develops: 2, 3

• Nausea, vomiting, or abdominal pain (especially right upper quadrant)
• Unusual fatigue or weakness
• Yellowing of skin or eyes
• Dark urine or pale stools

Elevated liver enzymes (AST >1000 IU/L) indicate severe hepatotoxicity, though most acute liver failure occurs with ingestions exceeding 10 grams per day. 2, 3