What is the appropriate intramuscular dose of Rocephin (ceftriaxone) for a healthy 15‑year‑old weighing 96 lb?

Rocephin IM Dose for 15-Year-Old, 96 Pounds

For a healthy 15-year-old weighing 96 lb (43.6 kg), administer ceftriaxone 50–75 mg/kg/day IM once daily for most infections, which translates to 2.2–3.3 grams daily; however, the pediatric maximum dose is 2 grams daily for non-meningeal infections, so the practical dose is 2 grams IM once daily. 1

Weight-Based Dosing Algorithm

Step 1: Convert weight and calculate dose range

• Patient weight: 96 lb = 43.6 kg
• Standard pediatric dosing: 50–75 mg/kg/day 1
• Calculated range: 2,180–3,270 mg/day

Step 2: Apply maximum dose limitation

• The FDA label explicitly states that the total daily pediatric dose should not exceed 2 grams for skin/soft tissue and serious miscellaneous infections (non-meningeal). 1
• For meningitis specifically, the maximum is 4 grams daily. 1

Step 3: Determine final dose by indication

For Most Infections (Non-Meningeal)

• Administer 2 grams IM once daily (the pediatric maximum, even though weight-based calculation suggests higher). 1
• This applies to pneumonia, skin/soft tissue infections, urinary tract infections, and other serious infections. 2, 1

For Bacterial Meningitis

• Administer 100 mg/kg/day (4.4 grams calculated), but cap at 4 grams daily maximum, divided as 2 grams IM every 12 hours. 1
• The initial dose may be given as 100 mg/kg (up to 4 grams). 1

For Uncomplicated Gonococcal Infections

• Administer 125 mg IM as a single dose. 3, 2
• This patient weighs <45 kg, so pediatric dosing applies. 3

Critical Considerations

Age and weight threshold:

• The CDC guidelines state that children weighing ≥45 kg should receive adult dosing regimens. 3, 2
• At 43.6 kg, this patient falls just below that threshold and should receive pediatric dosing with the 2-gram maximum for non-meningeal infections. 1

Route of administration:

• IM injection should be administered deep into a large muscle mass (gluteus or lateral thigh). 1
• Counsel the patient and family that IM injection of ceftriaxone is painful. 2, 4
• Aspiration before injection helps avoid unintentional intravascular administration. 1

Reconstitution for IM use:

• For a 2-gram vial, add 7.2 mL of diluent to achieve 250 mg/mL concentration. 1
• Alternatively, add 4.2 mL to achieve 350 mg/mL concentration. 1
• Use sterile water, 0.9% sodium chloride, or 5% dextrose solution. 1

Common Pitfalls to Avoid

Do not exceed pediatric maximum doses:

• Even though weight-based calculations may suggest 3+ grams, the FDA label caps non-meningeal infections at 2 grams daily in pediatric patients. 1
• Pediatric doses should never exceed adult maximum doses regardless of weight-based calculations. 2, 5

Do not use calcium-containing diluents:

• Never reconstitute with Ringer's solution or Hartmann's solution due to risk of precipitation. 1

Consider transition to adult dosing:

• At 96 lb (43.6 kg), this patient is very close to the 45 kg threshold where adult dosing (1–2 grams daily for most infections) would apply. 3
• For practical purposes, 2 grams IM once daily bridges both pediatric maximum and standard adult dosing. 1

Infection-specific adjustments:

• For severe infections with documented or suspected resistant organisms, consider 50 mg/kg twice daily (approximately 1 gram IM every 12 hours) rather than once-daily dosing to improve target attainment. 6
• For acute otitis media, a single 50 mg/kg dose (2.2 grams, capped at 2 grams) is sufficient. 1