Is a single 250 µg subcutaneous injection of romiplostim appropriate?

Romiplostim 250 mcg Single Dose Administration

A single 250 mcg dose of romiplostim is NOT appropriate—romiplostim must be dosed based on body weight at 1 mcg/kg/week initially, with weekly titration up to a maximum of 10 mcg/kg/week. 1, 2

Weight-Based Dosing is Mandatory

• Romiplostim is always dosed in mcg/kg, not as a fixed dose 1, 2
• The American Society of Hematology recommends an initial dose of 1 mcg/kg subcutaneously once weekly, with subsequent weekly adjustments by 1 mcg/kg increments based on platelet response 1
• A 250 mcg dose would only be appropriate for a patient weighing approximately 250 kg at the starting dose of 1 mcg/kg—this is not a realistic clinical scenario 1
• The maximum approved weekly dose is 10 mcg/kg, regardless of absolute dose in micrograms 2

Correct Dosing Algorithm for ITP

• Starting dose: 1 mcg/kg subcutaneously once weekly 1, 2
• Titration: Increase by 1 mcg/kg weekly until platelet count reaches ≥50 × 10⁹/L 1, 2
• Target range: Maintain platelet counts between 50-200 × 10⁹/L 1
• Maximum dose: Do not exceed 10 mcg/kg per week 1, 2
• Monitoring: Check platelet counts weekly during dose adjustment phase until stable 1

When Higher Initial Doses May Be Considered

While guideline-recommended dosing starts at 1 mcg/kg, emerging evidence suggests higher initial doses may be safe in specific circumstances:

• For hospitalized patients with severe, refractory ITP (platelet count <10 × 10⁹/L who failed corticosteroids and IVIg), initial doses of 2-4.5 mcg/kg achieved platelet ≥10 × 10⁹/L faster (median 2 days vs 4.5 days) compared to standard 1 mcg/kg dosing 3
• A retrospective analysis found that 51% of patients achieved platelets ≥50 × 10⁹/L by week 1 when median initial dose was 3.8 mcg/kg 4
• However, these higher initial doses remain off-label and should only be considered in severe, hospitalized cases under close monitoring 3, 4

Critical Safety Considerations

• Thrombotic risk: Exercise caution in patients with preexisting thrombotic risk factors, as thrombotic events occurred in 6.5% of patients in long-term studies 1
• Rebound thrombocytopenia: Worsening thrombocytopenia may occur upon abrupt discontinuation—always taper gradually 1, 2
• Liver monitoring: Although more relevant for eltrombopag, monitor for hepatic adverse events 5
• Bone marrow reticulin: Can occur but is typically mild, asymptomatic, and reversible; routine monitoring not required unless new cytopenias develop 1, 2

Expected Response Timeline

• Platelet response typically occurs within 1-4 weeks in patients with baseline counts <30 × 10⁹/L 5, 1
• Overall response rates: 88% in non-splenectomized patients, 79% in splenectomized patients 5, 1
• More than 80% of patients receiving adequate doses show platelet count increases by day 15 5

Common Pitfall to Avoid

The most critical error is administering romiplostim as a fixed dose rather than calculating the weight-based dose. Always calculate: patient weight (kg) × prescribed dose (mcg/kg) = total dose in mcg to administer. A 250 mcg dose would require knowing the patient's weight and intended dose per kilogram to determine appropriateness. 1, 2