Pharmacokinetics of amikacin and cephalothin in bedridden elderly patients

The pharmacokinetics of amikacin (5.5 mg/kg intramuscularly) and cephalothin (1000 mg/body intravenously) in bedridden elderly patients were studied in comparison with those in healthy volunteers. The eliminations of amikacin and cephalothin from the plasma followed the course of a one-compartment open model. For amikacin, five healthy volunteers, elimination rate constant Kel was 0.396 hr-1, biologic half-life t1/2 was 1.80 hour, volume of distribution Vd was 0.201 l./kg; in five bedridden elderly patients, Kel was 0.208 hr-1, t1/2 was 3.55 hours, Vd was 0.376 l./kg. Cumulative renal excretion of amikacin in 8 hours was 44 per cent of the total dose in bedridden elderly patients and 69 per cent in healthy volunteers. For cephalothin, in seven healthy volunteers, Kel was 0.0353 min-1, t1/2 was 19.7 min, Vd was 0.176 l./kg; in four bedridden elderly patients, Kel was 0.0127 min-1, t1/2 was 56.4 min, Vd was 0.283 l./kg. Cumulative renal excretion of cephalothin reached a plateau by 4 hours of 40.8 per cent of the total dose in bedridden elderly patients and of 56.7 per cent in healthy volunteers. These results suggest that in bedridden elderly patients decreased renal excretion of amikacin and cephalothin is related to decreased renal function and an increased Vd.