Loading Dose Calculator
Calculate initial loading doses to rapidly achieve therapeutic concentrations
Rapid Onset
Loading Dose Calculation
Target Concentration
Therapeutic concentration at steady state
Typical Ranges
Digoxin: 0.8-2.0 mcg/L
Vancomycin: 15-20 mg/L
Phenytoin: 10-20 mg/L
Vancomycin: 15-20 mg/L
Phenytoin: 10-20 mg/L
Volume of Distribution
Apparent volume of distribution
Loading Dose Formula
LD = (Cₚ × Vd) ÷ F
Where:
• Cₚ = Target plasma concentration
• Vd = Volume of distribution
• F = Bioavailability fraction (1 for IV)
• Cₚ = Target plasma concentration
• Vd = Volume of distribution
• F = Bioavailability fraction (1 for IV)
Example Drugs
Loading Dose
IV Loading Dose
Enter Values
Administration Guidance
IV Bolus:
Administer over 1-5 minutes
Divided Loading:
For large doses or risk of toxicity
Monitoring:
Check levels 30 min post-dose
Clinical Considerations
- • Adjust for renal/hepatic impairment
- • Consider protein binding changes
- • Monitor for adverse effects
- • Calculate maintenance dose separately
- • Verify with therapeutic drug monitoring
Advanced Loading Concepts
Divided Loading
• For drugs with long half-life
• Reduces toxicity risk
• Example: Digoxin 50% initial, then 25% q6-8h
• Allows assessment of response
Non-Linear Kinetics
• Phenytoin, Theophylline
• Michaelis-Menten kinetics
• Small dose increases cause large Cₚ changes
• Requires careful titration
Loading in Special Populations
• Elderly: Reduced Vd, increased sensitivity
• Obesity: Use adjusted body weight
• Renal failure: Reduced clearance
• Pediatrics: Different Vd/kg