Pharmacokinetics of chloramphenicol in the neonatal horse

Antimicrobial therapy for respiratory disease

Antimicrobial treatment is an important component of infectious respiratory disease management. However, across all systems in horses there is substantial deficit in definitive information concerning the efficacy of antimicrobials. This disassociation between laboratory data and antimicrobial efficacy and the obstacles to effective antimicrobial treatment should be understood.

The influence of age on the pharmacokinetics of aditoprim in pigs after intravenous and oral administration

Some pharmacokinetic parameters of aditoprim were determined in 3- and 6-month-old pigs. After intravenous administration of 5 mg/kg body weight, the mean total body clearance of the older pigs was smaller than that of the younger pigs. This difference was not reflected in the elimination half-life. After oral administration of 5 mg/kg body weight, the mean absorption rate constant was smaller and the mean absorption half-life was longer in the older pigs. The age-related changes in the pharmacokinetics of aditoprim were not sufficiently pronounced to suggest the necessity of modifying the oral dosage regimen in pigs of this age range. The favourable pharmacokinetics of aditoprim in pigs (large apparent volume of distribution, long elimination half-life and high bioavailability) may permit introduction of this drug into swine practice, after safety and residue depletion studies.

The pharmacokinetics of chloramphenicol in plasma and saliva of dairy cows

In the present study the pharmacokinetics of chloramphenicol were investigated in bovine plasma and saliva. The method of detection of chloramphenicol, a radio-immunoassay, requires only small sample volumes, no further clean-up, and a large number of samples can be processed simultaneously. This enabled the collection of a larger number of samples over a longer period of time than in previous studies. The intention was to obtain a complete pharmacokinetic profile of chloramphenicol, to evaluate it according to common open-compartment models, and to compare it with the results of previous studies. The radio-immunoassay results were confirmed by analysing a number of samples distributed over the concentration range of interest by a gas-chromatographic method with electron-capture detection. The suitability of saliva was evaluated as a possible means of monitoring compliance with the ban on chloramphenicol in the Federal Republic of Germany in milk-producing animals.

Pharmacologic considerations in drug therapy in foals

Rational drug therapy in the foal requires a sound knowledge of the pharmacodynamics and pharmacokinetics of various drugs as well as a thorough understanding of the physiologic differences that exist between the neonate and the adult and that may serve to alter drug disposition and, therefore, drug response. A summary of these physiologic factors with emphasis on the foal is presented and is followed by recommendations regarding the applied therapeutics of various antimicrobial agents.

Rational selection of antimicrobial drugs for treatment of infections of horses

The goal of antimicrobial drug use is quite specific. Consideration of many microbe-related, host-related, and drug-related factors is necessary for appropriate selection and use of antimicrobial drugs in equine patients. The concepts and data presented in this article demonstrate that fact. At the risk of oversimplification, "The bug denotes the drug, and the horse directs the course."

Inhibitory effects of intravenous chloramphenicol sodium succinate on the disposition of phenylbutazone in horses

The effects of i.v. chloramphenicol sodium succinate on the pharmacokinetics of i.v. phenylbutazone in six healthy adult horses were investigated. Administration of chloramphenicol sodium succinate to mares reduced mean (+/- SD) phenylbutazone clearance from 0.600 +/- 0.222 to 0.339 +/- 0.123 ml/min per kg and increased mean (+/- SD) half life from 244 +/- 59.8 to 371 +/- 80.8 min and mean residence time from 333 +/- 86.2 to 533 +/- 124 min. The mean steady-state volume of distribution of phenylbutazone was unchanged, with mean (+/- SD) values of 187 +/- 28.9 ml/kg in control animals and 170 +/- 32.4 ml/kg after chloramphenicol sodium succinate.

Aspects of pharmacology in the neonatal foal

Other therapeutic agents used in foals for specific diseases are discussed elsewhere. The marked effect of species, age, and degree of maturity on drug metabolism in the neonate reinforces the danger of interspecies extrapolation of pharmacology, the need for information specific for the foal, and the necessity for monitoring drug levels in the individual. Suggested antimicrobial doses are listed in Tables 3, 4, and 6. Recommended doses of anticonvulsants and sedatives are listed in Table 8 and in the article "Intensive Care of the Neonatal Foal." The following are recommendations for drug therapy in the neonate: Avoid unnecessary administration of drug to the dam at parturition because of possible placental transfer of the drug with subsequent effects on the neonate. If possible, avoid unnecessary drug therapy in foals under 30 days of age. Select a drug that undergoes minimal biotransformation (hepatic metabolism) and is not highly protein bound. Owing to probable immunodeficiency in the neonate, broad-spectrum, bactericidal drugs are preferred for treatment of life-threatening infections. Every attempt should be made to identify the etiologic agent so that drug therapy can be based on cultures and sensitivity test results to maximize the benefit-risk ratio. Parenteral (intramuscular or intravenous) drug administration is preferable to oral. Avoid drugs that are known oxidants, which may produce hemolysis or methemoglobinemia. In general, the same or a slightly higher initial dose should be employed in the neonate, but it should be given less frequently than in the adult if it has a high potential to cause toxicity. When possible, individual monitoring of serum levels of potentially toxic drugs should be employed in premature and newborn foals unless specific drug pharmacokinetics are known for that age group.

Pharmacokinetic aspects of penicillins, aminoglycosides and chloramphenicol in birds compared to mammals. A review

Based on a review of the literature, a comparison is made of the pharmacokinetics of penicillins, aminoglycosides, and chloramphenicol in birds and mammals. Penicillins in birds are likely to be more dependent for their elimination on biotransformation than in mammals. Amoxycillin had a relatively low availability (0.34) after p.o. administration. Higher doses (2 to 8 times) were needed to achieve the same peak levels in birds and mammals. Aminoglycosides, which for their elimination largely depend on renal excretion by glomerular filtration, show only minor differences in pharmacokinetics between birds and mammals. Chloramphenicol is mainly excreted after biotransformation and large differences in pharmacokinetic parameters are to be found, not only between birds and mammals, but also between avian species.

Drug disposition in the neonatal animal, with particular reference to the foal

Differences between neonatal and adult animals in their response to drugs can usually be attributed to altered disposition (ie, distribution, metabolism and excretion) processes during the neonatal period. These alterations affect the plasma concentrations as well as the concentrations of drug attained at the receptor site. Some characteristics of the neonatal period include greater absorption from the gastrointestinal tract, lower extent of plasma protein binding, increased apparent volume of distribution of drugs that distribute in extracellular fluid or total body water, increased permeability of the 'blood-brain' barrier and slower elimination of many drugs. The hepatic microsomal oxidative reactions and glucuronide conjugation are deficient metabolic pathways for a varying period of time, usually up to six weeks after birth or even longer in some species. Decreased metabolism can affect the duration of action of lipid-soluble drugs. Functional immaturity of the kidneys decreases the renal excretion of polar drugs and drug metabolites. Overall renal function appears to reach maturity within two weeks after birth in ruminant species and pigs, while maturation may take at least four weeks in other species of domestic animals. Considerable physiological and biochemical development takes place during the first five days after birth with maturation continuing more slowly over the succeeding five weeks. The time it takes for any process to reach functional maturity depends on the process in question and varies with the species of animal. The absorption, disposition and pharmacological response to drugs during the first 24 h after birth may be unique to that time and, because of lack of information, are impossible to predict.(ABSTRACT TRUNCATED AT 250 WORDS)