Ampicillin renal elimination

These are adapted from the ampicillin molecule, with a side-chain derived from urea. Their major advantages over the carboxypenicillins are higher efficacy against Pseudomonas aeruginosa and the fact that as monosodium salts they deliver on average about 2 mmol of sodium per gram of antimicrobial (see above) and are thus safer where sodium overload should particularly be avoided. They are degraded by many p-lactamases. Ureidopenicillins must be administered parenterally and are eliminated mainly in the urine. Accumulation in patients with poor renal function is less than with other penicillins as 25% is excreted in the bile. An unusual feature of their kinetics is that, as the dose is increased, the plasma concentration rises disproportionately, i.e. they exhibit saturation (zero-order) kinetics. 

Most are eliminated via active tubular secretion with half-life <60 min. Dose reduction needed only in major renal dysfunction. Nafcillin and oxacillin eliminated largely in bile ampicillin undergoes enterohepatic cycling, but is excreted by the kidney. Benzathine penicillin G—repository form (half-life of 2 weeks). 

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