Antimicrobial selection and dosage in the treatment of equine bacterial infections.

The success of antimicrobial therapy depends on administration of an agent to which the pathogenic microorganisms are susceptible at the concentrations attained at the site of infection. The route of administration, size of the dose and dosing interval must be appropriate for the drug preparation selected. With penicillins in particular, dosage can be tailored to the severity of the infection and quantitative susceptibility of the microorganism. This approach cannot be applied to aminoglycosides because their relatively narrow margin of safety limits the amount which can be administered. In severe infections it is important quickly to establish effective antimicrobial concentrations, which means that the choice of drug must be based on experience in treating the particular type of infection (empiric selection) and its dosage be adequate to produce a high peak concentration in the plasma. In treating septicaemic conditions of neonatal foals the deficit in serum immunoglobulins should be corrected, and it is advisable to administer antimicrobial agents or combinations that produce a bactericidal effect at dosages modified for immature physiological processes.