HED Scale Calculator
Convert drug doses between species using FDA Body Surface Area (BSA) normalization guidelines.
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pest_control Species A (Source)
accessibility_new Species B (Target)
Reference Body Weights (FDA Standard)
- Mouse: 0.02 kg
- Hamster: 0.08 kg
- Rat: 0.15 kg
- Ferret: 0.3 kg
- Guinea Pig: 0.4 kg
- Rabbit: 1.8 kg
- Dog: 10 kg
- Monkey: 3 kg
- Marmoset: 0.35 kg
- Baboon: 12 kg
- Micro Pig: 20 kg
- Mini Pig: 35 kg
- Human: 60 kg
menu_book The FDA Guide to Interspecies Dose Scaling
A critical milestone in pharmacological research and drug development is transitioning a novel therapeutic compound from preclinical animal models (e.g., murine or canine models) to Phase I human clinical trials. This process requires determining the Human Equivalent Dose (HED) to establish the Maximum Recommended Starting Dose (MRSD) for healthy volunteers.
warning Why Simple Weight Scaling is Dangerous
Historically, researchers scaled doses directly by body weight (mg/kg). For example, if a 20g mouse tolerated 10 mg/kg, they assumed a 60kg human could also tolerate 10 mg/kg. This is scientifically inaccurate and highly dangerous. Smaller animals have much higher basal metabolic rates and clear drugs significantly faster than larger animals. To account for this metabolic disparity, the FDA mandates that dose translation must be normalized to Body Surface Area (BSA), not just total body mass.
The Allometric Scaling Formula
To simplify BSA calculations, the FDA introduced the $K_m$ factor (where $K_m = \text{Body Weight (kg)} \div \text{BSA (m}^2\text{)}$). By dividing the animal's $K_m$ by the human's $K_m$, we get an accurate conversion ratio.
*Common $K_m$ values: Mouse (3), Rat (6), Dog (20), Adult Human (37).
Frequently Asked Questions (FAQ)
What is the difference between "Equivalent Dose (mg/kg)" and "Absolute Dose (mg)"?
The Equivalent Dose is the concentration of the drug normalized to the target species' weight (e.g., 2.4 mg of drug per 1 kg of human). The Absolute Dose is the total physical amount of the drug you must administer to the specific subject. Our calculator provides the Absolute Dose if you input the target subject's specific body weight.
Can I use this formula for pediatric (children) clinical trials?
No. The standard human $K_m$ factor of 37 is based on a standard healthy adult weighing 60 kg. Children and infants have a drastically different Body Surface Area-to-weight ratio compared to adults. Pediatric dose scaling requires specific allometric formulas that account for developmental pharmacokinetics.
Does this formula apply to all types of administration?
BSA normalization is primarily designed for drugs administered systemically (e.g., Intravenous (IV) or Oral (PO)). It is generally not appropriate for drugs administered topically (on the skin), intramuscularly, or via local injection, as these do not scale directly with systemic basal metabolic rate.