High rate of metabolism – impact on drug clearance:

The rat’s high rate of metabolism produces a rapid clearance of drugs from the body. Drugs administered at dose rates used in larger species (with lower metabolic rates) would reach lower blood concentrations and exert less pharmacological effect in the rat. As a result, rats should receive drug doses that have been scaled to the rat’s metabolism. Through a discipline known as allometry, mathematical formulas have been developed to adjust dose rates between species of disparate size.

In general, rat-specific dose rates have been determined and are widely published for drugs that are commonly used in animal research, such as anesthetics, analgesics, sedatives, and antibiotics. Investigators are advised to obtain rat dose rates from laboratory animal references or from their institution's veterinary staff.