Dosage Conversion Error: You Will Be Giving Half the Dose
If you administer 5 units of the 2.5mg/mL formulation, your patient will receive only 12.5mg weekly instead of the previous 25mg weekly—this represents a 50% dose reduction that could compromise glycemic control.
Understanding the Concentration Change
The critical issue here is concentration, not volume:
- Previous formulation: 5mg/mL concentration means 5 units (0.05mL) delivered 25mg weekly 1
- New formulation: 2.5mg/mL concentration means 5 units (0.05mL) delivers only 12.5mg weekly 1
The volume remains the same (5 units), but the amount of active drug is cut in half due to the lower concentration 1.
Correct Dosing Strategy
To maintain the same therapeutic dose of 25mg weekly, you must administer 10 units of the 2.5mg/mL formulation 2, 1.
Dose Calculation
- Target dose: 25mg weekly (patient's established dose)
- New concentration: 2.5mg/mL
- Required volume: 25mg ÷ 2.5mg/mL = 10mL = 10 units 1
Clinical Implications of Underdosing
Inadvertently reducing the dose by 50% will likely result in:
- Loss of glycemic control: Mean HbA1c reductions are dose-dependent, with higher doses achieving greater reductions (1.21% reduction with 0.5mg vs 1.64% with 1.0mg weekly) 3, 4
- Reduced weight loss benefits: Weight loss is dose-dependent, with 2.0mg achieving -6.9kg vs -6.0kg with 1.0mg 5
- Potential disease progression: Suboptimal dosing may necessitate addition of other medications or insulin 2
Verification Steps Before Administration
- Confirm the concentration on the new vial label (should read 2.5mg/mL) 1
- Calculate required units: Divide target dose (25mg) by concentration (2.5mg/mL) = 10 units 1
- Verify pen/syringe markings correspond to the new concentration 1
- Document the formulation change in the patient's medical record 6
Common Pitfall to Avoid
Never assume "5 units equals 5 units" across different formulations—always verify the concentration and recalculate the volume needed to deliver the same milligram dose 1. This is a high-risk medication error that could significantly impact patient outcomes 2.