A simple method for the estimation of glomerular filtration rate by gentamicin pharmacokinetics during routine drug monitoring in the newborn.

Assessment of the glomerular filtration rate (GFR) in the newborn is often imprecise because of difficulties in urine collection and because the plasma creatinine level, the traditional marker of renal function, is influenced by many factors in this age group. Gentamicin is given to most preterm infants for suspected or proved sepsis. This drug is eliminated almost entirely by the kidney and its rate of elimination parallels the GFR. We calculated gentamicin pharmacokinetic parameters (t1/2, volume of distribution, and clearance) from three consecutive concentration-time points (trough, peak, and next trough levels) in 38 newborn infants. Creatinine clearance was measured by the conventional method. Both t1/2 (r = 0.74; P less than 0.001) and gentamicin clearance (r = 0.77; P less than 0.001) correlated well with measured creatinine clearance. There was no correlation between these variables and urine output. Gentamicin elimination t1/2 and clearance are useful indices of GFR in the newborn infant and can be easily calculated during routine therapeutic drug monitoring.