Elimination

Renal (unchanged) and dosing tends to be consistent between species

Distribution

usually (and in practical terms) limited to extracellular space. Doses (/kg) are consistant between species and individuals with same % ECF. For aminoglycosides: dose adjustments are made for neonates based on altered ECF. For cephalosporins: some third generation drugs have improved tissue penetration

Absorption

For aminoglycosides: virtually no oral absorption (though sufficient absorption still occurs to produce kidney residues with prolonged oral administration). For aenicillins. oral absorption is moderate to poor (absorption depends on drug selection). Oral absorption modified more by acid resistance than by lipid solubility. Differences in solubility affect antibacterial activity more than oharmacokinetics. For cephalosporins:oral absorption is variable by generic drug some are well absorbed, some poorly, some not at all). For all drugs: im, sc sbsorption is very good, best for neutral salts. For penicillins: products often iesigned to slow absorption and produce sustained effect by salt formulation procaine, benzathine).