Medication Dose Calculation
For an 81.4 kg patient requiring 10 mg/kg/day divided into three equal injections using an 80 mg/2 mL (40 mg/mL) solution, administer 6.8 mL per injection.
Calculation Breakdown
Step 1: Calculate Total Daily Dose
- Patient weight: 81.4 kg
- Required dose: 10 mg/kg/day
- Total daily dose = 81.4 kg × 10 mg/kg = 814 mg/day
Step 2: Calculate Dose Per Injection
- Total daily dose divided into 3 equal injections
- Dose per injection = 814 mg ÷ 3 = 271.3 mg per injection
Step 3: Convert to Volume Using Available Concentration
- Available concentration: 80 mg/2 mL = 40 mg/mL
- Volume per injection = 271.3 mg ÷ 40 mg/mL = 6.78 mL ≈ 6.8 mL
Clinical Context for Weight-Based Dosing
When administering weight-based medications, particularly in the context of injectable therapies:
Streptomycin dosing for tuberculosis in adults uses 15 mg/kg/day (maximum 1 g/day) parenterally, typically as a single daily dose initially, with frequency reduction after 2-4 months 1
Enoxaparin dosing for venous thromboembolism uses 1 mg/kg subcutaneously every 12 hours for patients with BMI <40 kg/m², or 0.8 mg/kg every 12 hours for BMI ≥40 kg/m² 1
For patients >59 years receiving streptomycin, the dose should be reduced to 10 mg/kg/day (750 mg maximum) 1
Important Considerations
- Verify the concentration of your available solution before each administration (80 mg/2 mL = 40 mg/mL in this case)
- Round appropriately based on syringe graduations available (6.8 mL is the precise calculation)
- Monitor for dose-dependent adverse effects, as therapeutic effectiveness and adverse events are closely related to both dose and administration rate 1
- Adjust dosing frequency in patients with renal insufficiency if using medications with predominantly renal clearance 1