Gentamicin volume of distribution as a power function of body weight.

Gentamicin volume of distribution (V) was related to body weight (W) in 183 obese, normal weight and infant patients as reported in five published studies. In contrast to the usually postulated simple proportionality (V = bW) a linear function was found (V = a + bW) with an intercept (a = 2.5 +/- 0.49) significantly different from zero (P = 0.0001) and a slope (b = 0.19 +/- 0.10) significantly different (P = 0.0001) from the mean factor of proportion (b = 0.35 +/- 0.19). As compared with the linear function, a power function (V = 0.57 W 0.79) approximated even more closely the dependence of gentamicin volume on body weight (r = 0.94 vs r = 0.81). The difference between both functions was more than 50% only for body weight less than 5 kg. It is concluded that the relation between gentamicin volume of distribution and body weight is non-linear.