Comparative pharmacokinetics of aminoglycoside antibiotics in guinea pigs

The pharmacokinetics of netilmicin, gentamicin, and tobramycin in plasma and in perilymph of guinea pigs were studied after a single intravenous injection of 40 mg/kg. Detailed pharmacokinetic analysis of the plasma drug concentration-time data up to 36 h after the intravenous dose revealed that the pharmacokinetics of the aminoglycoside antibiotics can be best described as a three-compartment open model. The disposition half-lives (t1/2) in plasma of the three antibiotics were comparable and within the following ranges: t1/2 alpha of 0.09 to 0.16 h; t1/2 beta of 0.88 to 1.01 h; and t1/2 gamma of 7.87 to 8.29 h. The volume of distribution in the central compartment and the total body clearance of netilmicin (294 ml/kg, 5.74 ml/min per kg) were greater than those of gentamicin (160 ml/kg, 3.40 ml/min per kg) and tobramycin (204 ml/kg, 4.63 ml/min per kg). Pharmacokinetic analysis of the perilymph drug concentration-time data indicated that all three antibiotics penetrated the perilymph readily, but netilmicin cleared from the perilymph compartment faster than gentamicin and tobramycin. The maximum perilymph drug concentrations were 4.17, 8.05, and 6.78 micrograms/ml and occurred at 1, 2, and 4 h for netilmicin, gentamicin, and tobramycin, respectively. The ratio of area under the curve of perilymph to plasma was lowest for netilmicin (0.27), followed by gentamicin (0.39) and tobramycin (0.57). These results suggest that the differences in pharmacokinetics and concentrations of netilmicin in the perilymph may account for less ototoxic liability of netilmicin compared with gentamicin and tobramycin.

Effect of body weight on postnatal development of the proximal small intestine of the rabbit

The effect of oral intake and body weight on postnatal maturation of the small intestine was examined in infant rabbits with accelerated weight gain. Intestine from immature animals is characterized by large unidirectional Na fluxes, failure of Na absorption to respond to glucose but increased ability to absorb monosaccharides, and an enzyme pattern of high lactase and thymidine kinase and low sucrase. Postnatal development was monitored by measuring Na and glucose transport in short-circuited jejunum and enzyme activities in jejunal mucosa. Accelerated weight gain was achieved in the experimental group by reducing litter size to 3 animals at 24-48 hours of age. Under glucose-free conditions unidirectional Na fluxes were significantly smaller in tissue from the heavier experimental animals compared to controls. The addition of glucose had no effect on Na fluxes in control tissue but significantly increased Na absorption in the experimental group. Unidirectional and net fluxes of 14C-D-glucose were significantly smaller in the heavy experimental animals compared to controls. Isolated villus enterocytes from the experimental group had reduced lactase and thymidine kinase activities. Sucrase activity, which did not differ in isolated cells, was increased in total mucosa from the experimental group. Solute transport and the enzyme profile in jejunum from the heavier experimental suckling rabbits is characteristic of intestinal epithelium from more mature animals, indicating accelerated postnatal maturation. The findings suggest that oral nutrient intake and body weight, rather than chronologic age, act as the physiologic trigger for postnatal maturation of the small intestine.

Pharmacokinetic study of sisomicin in humans

Detailed analyses of the pharmacokinetics of sisomicin administered at doses of 25, 50 and 100 mg intravenously and intramuscularly to healthy volunteers established that the drug is handled by a two-compartment open model system with a disposition (elimination) half-life of 2.6 hr. The kinetic estimates over this dose range are linear and independent of dose and were verified by a 60-min infusion experiment in which dose and the maximum serum concentration achieved (5 microgram/ml) were predicted correctly. Sisomicin was rapidly distributed to the tissue compartment, and equilibrium between the central and the tissue compartment was established by 30 min after dosing. Renal clearance (55 ml/min) of sisomicin was about 30% less than total body clearance (78 ml/min). Total urinary excretion of sisomicin during a 24-hr period following drug administration was about 70% of the dose. The disposition kinetics of sisomicin following intramuscular administration are similar to those obtained following rapid intravenous administration. Intramuscular bioavailability of sisomicin for the doses of 25, 50, and 100 mg was greater than 95%. Based on these results, various initial loading infusion doses and maintenance infusion rates were calculated to provide specific desired peak and steady-state serum sisomicin concentrations rapidly. The purpose was not to expose patients to potentially toxic high peak concentrations of drug while maintaining these concentrations during the current therapeutic dosing intervals of 8 to 12 hr.

Bioavailability of orally administered propiram fumarate in humans

Propiram bioavailability was determined in 10 healthy volunteers after a single role administration of 50 mg (base equivalent) of propiram fumarate in tablet or solution dosage from in a randomized crossover design. The plasma drug concentration-time curve revealed a one-compartment open model with first-order absorption kinetics. There were no statistically significant differences (P greater than 0.05) between all of the measured pharmacokinetic parameters obtained from the tablet and the solution with the exception of the absorption lag time (tlag), where the tablet had a significantly longer tlag. The drug given as a tablet or solution was absorbed rapidly after oral administration with an apparent absorption rate constant of 3.7 hr-1 for both dosage forms. The Cmax value (308 ng/ml for the tablet and 342 ng/ml for the solution) was attained at approximately 1 hr after oral administration. The elimination half-life was 5.2 hr for the tablet and 4.4 hr for the solution, and the apparent distribution volume was 2.31 liters/kg for the tablet and 1.94 liters/kg for the solution. Total body clearance was much greater than renal clearance, indicating extensive metabolic clearance for both dosage forms. The study showed that propiram administered as the tablet was bioequivalent to the solution.

Comparison of netilmicin and gentamicin pharmacokinetics in humans

In a crossover study, single doses of netilmicin and gentamicin were administered intramuscularly, each at 1.0 and 2.5 mg/kg. The serum concentrations, analyzed by a two-compartment open model with a first-order absorption, indicated that the pharmacokinetics of the drugs are essentially the same. Both drugs were rapidly absorbed and distributed after administration. No significant differences were observed between the two drugs in disposition half-life, rate of distribution and elimination, area under the serum concentration-time curve, urinary excretion, total body clearance, and renal clearance. After 1.0 mg/kg, the maximum serum concentration of netilmicin (5.18 microgram/ml) was only slightly lower than that for gentamicin (5.76 microgram/ml), but no difference was found after the 2.5-mg/kg dose.