Body composition analysis by bioelectrical impedance: the effects of time of day and body side on estimated gentamicin pharmacokinetics.

To assess if repetitive measures are useful in a clinical setting, the effects of time of day and body side on bioelectrical impedance (BI) measurements were evaluated. Fifteen healthy, male volunteers underwent serial BI measurements at 0, 3, 6, 9, 24, and 48 hours on both sides of the body using a four-electrode plethysmograph. Analysis of variance for repeated measures indicated that the mean resistance (R) value of the right side was statistically lower from that of the left side (447 +/- 27.9 vs 457 +/- 29.1 ohms; p = 0.006). Both R and reactance (Xc) varied significantly over time. For R, the mean response at 0, 6, 9, and 48 hours was different from the overall mean of the remaining time points (p less than 0.007). Only times 6 and 24 hours were significantly different for Xc (p less than 0.006). No relevant time and side effects were noted in calculated gentamicin pharmacokinetic parameters on incorporation of BI measurements into impedance-derived predictive equations for clearance, volume of distribution, and elimination constant. Correlation coefficients of reliability were high within 1 day and across days (R greater than or equal to 0.8407). These data suggest that under normal conditions, BI analysis provides reliable results, and that time and side standardizations in its measurements are not necessary.