Effect of polyaspartic acid on pharmacokinetics of gentamicin after single intravenous dose in the dog

Dihydrostreptomycin or streptomycin in combination with penicillin G in dairy cattle therapeutics: A review and re-analysis of published data Part 2: Resistance and residues

Combination formulations of penicillin G salts and dihydrostreptomycin were developed during the 1960s and are currently marketed in New Zealand for parenteral and intramammary use in dairy cattle. In this paper, the second part of a two paper series, the mechanisms by which bacteria develop resistance to each of these drugs independently is reviewed and the impact of this resistance on potential for synergy is discussed. Further, the considerable potential for tissue drug residues with dihydrostreptomycin or streptomycin from these formulations is examined by re-analysis of literature data, demonstrating an urgent need to reassess the place for aminoglycoside-containing formulations in dairy cattle therapeutics.

A simulation model for the prediction of tissue:plasma partition coefficients for drug residues in natural casings

Tissue residues arise from the exposure of animals to undesirable substances in animal feed materials and drinking water and to the therapeutic or zootechnical use of veterinary medicinal products. In the framework of this study, an advanced toxicokinetic model was developed to predict the likelihood of residue disposition of licensed veterinary products in natural casings used as envelope for a variety of meat products, such as sausages. The model proved suitable for the calculation of drug concentrations in the muscles of pigs, cattle and sheep, the major species of which intestines are used. On the basis of drug concentrations in muscle tissue, the model allowed a prediction of intestinal concentrations and residues in the intestines that remained equal to or below the concentrations in muscle tissue, the major consumable product of slaughter animals. Subsequently, residues in intestines were found to be below the maximum residue limit value for muscle tissue when drugs were used according to prescribed procedures, including the application of appropriate withdrawal times. Considering the low consumption of natural casings (which represents only about 1-2% of the weight of a normal sausage), it was concluded that the exposure to drug residues from casings is negligible.

Reduced renal toxicity of nanoparticular amphotericin B micelles prepared with partially benzylated poly-L-aspartic acid

A partially benzylated poly-L-aspartic acid (PBPA) was synthesized and investigated as a potential renal protective agent for the toxicity of amphotericin B (AmB) when the drug was administered as nanoparticular micelle. Nanoparticular AmB micelles were prepared by slow dialysis of the drug against distilled water at the elevated pH of 11.5 and subsequent sonication with the polymer solution. The resulting nanoparticular AmB micelles with PBPA showed an average diameter of about 20 nm and demonstrated significantly less damage to the tubular cells of the rat's kidney in terms of transmission electron microscopic study. There was little or no damage on the brush border of tubular cells 7 d after single intravenous dose of AmB 5 mg/kg in the rats when the drug was administered as nanoparticuar micelles with PBPA. The reduced renal toxicity appears to be due to the alteration of self-aggregation status of AmB. Molar absorptivity of AmB at 412 nm (a marker for the prevalence of non-aggregated AmB) was significantly higher in the nanoparticular AmB micelles with PBPA than those in AmB micelles without PBPA as well as in Fungizone. This result indicates an association of the reduced nephrotoxicity and the prevalence of non-aggregated AmB. Mechanisms for the reduced renal toxicity may also include the formation of electrostatic complex between anionic groups of PBPA and hydroxyl groups of AmB.

Species-specific uncertainty factors for compounds eliminated principally by renal excretion in humans

An uncertainty factor of 100 is used to derive health-based guidance values for human intakes of chemicals based on data from studies in animals. The 100-fold factor comprises 10-fold factors for species differences and for interindividual differences in response. Each 10-fold factor can be subdivided into toxicokinetic and toxicodynamic aspects with a 4.0-fold factor to allow for kinetic differences between test species and humans. The current work determined the extent of interspecies differences in the internal dose (toxicokinetics) of compounds which are eliminated primarily by renal excretion in humans. An analysis of the published data showed that renal excretion was also the main route of elimination in the test species for most of the identified probe substrates. Interspecies differences were apparent for both the mechanism of renal excretion (glomerular filtration, tubular secretion and/or reabsorption) and the extent of plasma protein binding, both of which may affect renal clearance and therefore the magnitude of species differences in the internal dose. For compounds which are eliminated unchanged by both humans and the test species, the average differences in the internal doses between humans and animals were 1.6 for dogs, 3.3 for rabbits, 5.2 for rats and 13 for mice. This suggests that for renal excretion, the differences between humans and the rat and especially the mouse may exceed the 4.0-fold default factor for toxicokinetics.

Multiple once-daily dose pharmacokinetics and renal safety of gentamicin in dogs

In this study the pharmacokinetics and renal safety of gentamicin in healthy dogs was investigated after multiple dosing. Six adult male dogs received once-daily gentamicin (6 mg/kg) intramuscularly for 5 days. Serial blood samples were taken on days 1 and 5 of treatment, and at predose, 1 and 6 h on days 2, 3 and 4. Urinalysis, hematology and serum biochemistry evaluation were carried out before, 7 and 14 days after the first gentamicin administration. Mean value of the main pharmacokinetic parameters were: AUC (microg.h/mL), 97.4 and 100.2; terminal half-life (harmonic mean), 0.76 and 1.01 h; ClB/F (mL/min.kg), 1.24 and 1.10; VD(area)/F (L/kg), 0.084 and 0.10; MRT (h), 1.48 and 1.77; Cmax (microg/mL), 54.5 and 49.2; tmax (h), 0.40 and 0.48 for the first and last dose, respectively. Accumulation was determined as R1 = 0.97 and R2 = 1.22. Mean trough gentamicin serum concentrations were 0.06, 0.07, 0.09, 0.1 and 0.1 microg/mL for the first, second, third, fourth and fifth dose, respectively. Statistically significant increases (P < 0.05) were found for last dose MRT and fourth and fifth trough gentamicin serum concentrations. Laboratory tests detected a slight increase in serum creatinine and urea nitrogen concentrations (one dog), decreased specific urine gravity (one dog) and presence of few granular casts (two dogs). It is concluded that once-daily administration of gentamicin may provide adequate serum levels to treat most susceptible gram-negative infections with little or no nephrotoxicity in dogs.

Pharmacokinetics of gentamicin C(1), C(1a), and C(2) in beagles after a single intravenous dose

The pharmacokinetics of gentamicin C(1), C(2), and C(1a) were studied in six beagles after administration of gentamicin at 4 mg/kg of body weight as a single intravenous bolus dose. Plasma concentrations of the gentamicin components were analyzed with a novel high-performance liquid chromatography method capable of identifying and quantifying each of the components. The pharmacokinetic analysis of the plasma concentration-versus-time data was performed using the noncompartmental approach. The results indicated significant differences in the pharmacokinetic characteristics between the gentamicin components C(1), C(1a), and C(2). The mean residence times of gentamicin C(1), C(1a), and C(2) were 81+/-13, 84+/-12, and 79+/-13 min (mean +/- standard deviation), respectively. The half-lives of the respective components were 64+/-12, 66+/-12 and 63+/-12 min. Clearance (CL) of gentamicin C(1), 4.62+/-0.71 ml min(-1) kg(-1), was significantly higher (P = 0.0156) than CL of gentamicin C(1a), 1.81+/-0.26 ml min(-1) kg(-1), and C(2), 1.82+/-0.25 ml min(-1) kg(-1). Similarly, the volume of distribution at steady state (V(ss)) of gentamicin C(1), 0.36+/-0.04 liter kg(-1), was significantly higher (P = 0.0156) than the V(ss) of gentamicin C(1a), 0.14+/-0.01 liter kg(-1), and C(2), 0.15+/-0.02 liter kg(-1). Tissue binding was considered the most likely cause for the difference. The difference may have clinical and toxicological significance.