Allometric scaling for prediction of clinical PK parameters from preclinical data.

ALLOMETRICA is a program for fitting an allometric equation to data for pharmacokinetic or pharmacodynamic parameters from several species, or conversely for predicting a parameter value from an existing allometric equation.  ALLOMETRICA will also search a database to determine whether existing allometric parameters are already on file.

Allometric scaling is often used in drug development to predict the probable behaviour in humans of an experimental drug that is to be taken into clinical trials.  Its accuracy varies, but it is almost always better than guesswork, or simple scaling on the basis of body weight or surface area.  The figure shows a typical example of allometric scaling being used to predict the human volume of distribution of an HIV protease inhibitor from preclinical data.  Based upon measured values in rats, marmosets, dogs, and monkeys, the allometric equation was shown to be:

                                                log(Vd) = 0.546 – 0.1478 log(W)

where W is body weight in kg.  For a 70 kg human, this predicts a volume of distribution of 1.88 L/kg.  The value measured in the clinical trial was 1.5 L/kg.

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