Pharmacokinetics and bioavailability of ticarcillin and clavulanate in foals after intravenous and intramuscular administration

Renal pharmacology

Pharmacologic treatment of diseases of the urinary tract of horses is limited to administration of antibiotics for treatment of urinary tract infections (UTIs), administration of drugs that alter urine pH, administration of drugs that alter bladder smooth muscle function or urethral sphincter tone, and treatment of acute renal failure. The indications, mechanisms of action, pharmacokinetic characteristics, and adverse effects of these agents in each of these groups are discussed in this article. The use of the agents is discussed within the context of the pathophysiology of the disease being treated.

Pharmacologic considerations in the treatment of neonatal septicemia and its complications

This article focuses on the pharmacologic properties of drugs commonly used in the treatment of neonatal septicemia and its complications. Rational therapy demands an awareness of not only the pharmacology of individual drugs but also the interactions and anticipated fate of such drugs in the rapidly changing physiologic environment of the neonate. Further research in the area of equine neonatal pharmacology should greatly assist our understanding of the impact of the disease state on the unique physiology of the newborn and should allow us to better predict the ultimate fate of drugs commonly used for such purposes. Careful dosing and close monitoring of pharmacologic effects are critical for a successful outcome. In the future, newer therapeutic strategies that are safe and efficacious may provide a means to circumvent many of the problems currently encountered with treating the septicemic newborn foal.

Pharmacokinetics of amoxicillin/clavulanic acid combination and of both drugs alone after intravenous administration to goats

The pharmacokinetic behaviour of an amoxicillin/clavulanic acid combination (25 mg kg-1), and both drugs alone (amoxicillin 20 mg kg-1), clavulanic acid 5 mg kg-1), was studied after intravenous (i.v.) administration of single doses of 10 goats. The objective was to determine whether there were differences in the plasma kinetics of these drugs when administered in combination or alone. The plasma concentration-time data were analysed by compartmental pharmacokinetics and non-compartmental methods. The disposition curves for both drugs alone and in combination were best described by a biexponential equation (two-compartment open model). The elimination half-lives of amoxicillin were 1.05 +/- 0.09 h alone and 1.13 +/- 0.19 h in combination, and those of clavulanic acid were 0.87 +/- 0.07 h and 0.85 +/- 0.09 h, respectively. The apparent volumes of distribution of amoxicillin and clavulanic acid were similar in the two treatments. Body clearances of amoxicillin were 0.12 +/- 0.01 l h-1.kg alone and 0.11 +/- 0.01 l h-1.kg in combination, and of clavulanic acid were 0.12 +/- 0.02 l h-1.kg alone and 0.12 +/- 0.01 l h-1.kg in combination with amoxicillin. The half-lives and body clearances of amoxicillin and clavulanic acid did not differ significantly when administered alone and in combination. It was concluded that the i.v. administration of amoxicillin and clavulanic acid as a combination product did not alter the disposition kinetics of either drug.

Comparative pharmacokinetics of amoxicillin/clavulanic acid combination after intravenous administration to sheep and goats

The pharmacokinetic behaviour of an amoxicillin/clavulanic acid combination was studied after intravenous administration of single doses (20 mg/kg per kg body weight) to five sheep and six goats. The objective was to determine whether there are differences between sheep and goats in the disposition of amoxicillin and clavulanic acid. The plasma concentration-time data were analysed by compartmental pharmacokinetic and non-compartmental methods. The disposition curves for both drugs were best described by a biexponential equation (two-compartment open model) in sheep and goats. The elimination half-lives of amoxicillin were 1.43 +/- 0.16 h in sheep and 1.13 +/- 0.19 h in goats, and of clavulanic acid were 1.16 +/- 0.01 h and 0.85 +/- 0.09 h in sheep and goats respectively. The apparent volumes of distribution of amoxicillin and clavulanic acid were similar in the two species. Body clearances of amoxicillin were 0.09 +/- 0.01 L/h kg in sheep and 0.11 +/- 0.01 L/h kg in goats, and of clavulanic acid were 0.07 +/- 0.01 L/h kg and 0.12 +/- 0.01 L/h kg in sheep and goats respectively. The half-lives and body clearances of amoxicillin and clavulanic acid differed significantly between sheep and goats. It was concluded that the disposition of amoxicillin and clavulanic acid administered intravenously as an amoxicillin/clavulanic acid combination to sheep and goats differed between the two ruminant species. Even though the differences in disposition kinetics of both drugs were statistically significant, the same intravenous dosing rate of this antimicrobial combination can generally be used in sheep and goats.

Drug therapy in the neonatal foal

The neonatal period in foals refers to the first 7 days of postnatal life. The effects of drugs (pharmacologic agents) may be different in neonatal foals, particularly during the first 3 days of postnatal life, from those in older foals and adult horses. The changed drug effects decrease as the physiologic processes that affect absorption, distribution, and elimination (metabolism and excretion) of drugs mature. Dosage regimens should take into account the altered pharmacokinetic profiles of drugs, and because of wide individual variation, the response to therapy should be closely monitored for signs of toxicity. In conjunction with the prudent use of drugs, good nursing care and the provision of supportive therapy are critical in the management of neonatal foal diseases. Over-crowding imposes stress upon young foals and predisposes them to an increased incidence of bacterial and parasitic infections. The collection of specimens for precise microbiologic diagnosis and correction of deficits in serum immunoglobulins should precede antimicrobial therapy. Although E. coli is by far the most common cause of bacterial infections in neonatal foals, other bacterial pathogens of unpredictable susceptibility often cause infection. The selection of an antimicrobial drug for specific therapy should be based on both the microbiologic (quantitative susceptibility) and pharmacologic (pharmacokinetic) properties of the drug. The use of an antimicrobial drug or combination of drugs that will produce a bactericidal effect is highly desirable. Whenever possible, a parenteral preparation that can be administered intravenously should be chosen. The bioavailability and selectivity of action of pharmacologic agents are influenced by the dosage form and route of administration. Diazepam is the sedative drug of choice for neonatal foals. Cimetidine, an H2-receptor antagonist, may be indicated in foals diagnosed to have gastric ulcers; hepatic microsomal oxidative metabolism of drugs administered concurrently with cimetidine is decreased. Nonsteroidal anti-inflammatory drugs (flunixin, phenylbutazone) have a higher incidence of toxicity in foals and, when indicated, should be used at lower dosage than in adult horses. Even though it is highly important to maintain hydration status and electrolyte balance, intravenous infusion should always be performed slowly. Immature renal function decreases the ability of the neonatal animal to excrete excess fluid. The use of drugs in neonatal foals requires greater precision in dosage, more attention to the route and rate of administration, and close monitoring of pharmacologic effects.