Ofirmev (Intravenous Acetaminophen) Dosing Interval
For adults weighing ≥50 kg, Ofirmev should be administered either 1,000 mg every 6 hours OR 650 mg every 4 hours, with a minimum dosing interval of 4 hours between doses. 1
Standard Dosing Intervals by Weight
Adults and Adolescents ≥50 kg
- Primary regimen: 1,000 mg every 6 hours 1
- Alternative regimen: 650 mg every 4 hours 1
- Minimum interval: 4 hours between any doses 1
- Maximum single dose: 1,000 mg 1
- Maximum daily dose: 4,000 mg per day (including all routes and acetaminophen-containing products) 1
Adults and Adolescents <50 kg
- Dosing: 15 mg/kg every 6 hours OR 12.5 mg/kg every 4 hours 1
- Minimum interval: 4 hours between doses 1
- Maximum single dose: 15 mg/kg 1
- Maximum daily dose: 75 mg/kg per day 1
Administration Guidelines
Each dose must be infused over 15 minutes, regardless of the volume administered 1. This infusion time applies to all patient populations and dose sizes.
For the 1,000 mg dose in patients ≥50 kg, the entire 100 mL vial may be administered without dilution using a vented IV set 1. For doses less than 1,000 mg, the appropriate volume must be withdrawn using aseptic technique and placed in a separate sterile container before administration 1.
Critical Safety Considerations
Maximum Daily Dose Limits
The 4,000 mg maximum daily dose includes all sources of acetaminophen: intravenous, oral, rectal, and combination products containing acetaminophen 1. Exceeding this limit may result in hepatic injury, liver failure, and death 1.
However, increasingly conservative recommendations suggest limiting chronic use to 3,000-3,250 mg per day to reduce hepatotoxicity risk 2. For patients with liver disease or chronic alcohol use, the maximum should be reduced to 2,000-3,000 mg per day 3, 2.
Timing and Stability
Once the container seal is penetrated or contents transferred to another container, administer within 6 hours 1. Monitor the end of infusion to prevent air embolism, especially when Ofirmev is the primary infusion 1.
Common Pitfalls to Avoid
- Failing to account for combination products: Many patients receive opioid-acetaminophen combinations or take OTC products containing acetaminophen, leading to unintentional overdose 2
- Not adjusting for high-risk patients: Those with liver disease, chronic alcohol use, malnutrition, or fasting states require lower maximum daily doses (2-3 grams) 3, 2
- Administering too frequently: The absolute minimum interval is 4 hours; do not shorten this interval even if pain control is inadequate 1
- Using the entire 100 mL vial for patients <50 kg: This population requires weight-based dosing with the appropriate volume withdrawn into a separate container 1
Evidence Quality Note
The FDA-approved dosing interval of every 4-6 hours is supported by pharmacokinetic studies showing that IV acetaminophen in neonates, infants, and adults achieves similar PK profiles with these intervals 4. Safety data from multiple-dose studies over 5 days demonstrate tolerability with both the every-4-hour and every-6-hour regimens 5. However, rare cases of hepatotoxicity have been reported even with therapeutic IV dosing 6, reinforcing the importance of adhering to maximum daily dose limits and monitoring high-risk patients.