Ceftazidim

The bacterial cell wall, which is located at the periphery of Gram-positive bacteria and within the periplasm of Gram-negative bacteria, comprises a glycopeptide polymer synthesized through cross-linking of glycans to peptide stems on alternating saccharides, which is known commonly as peptidoglycan. Cell wall formation, recycling, and remodelling require numerous enzymes, including a family of enzymes with similar active site character despite distinct and sometimes overlapping roles as carboxypeptidases, endopeptidases, transpeptidases, and transglycosylases, known as "penicillin-binding proteins" (PBPs). The number of PBPs differs between bacteria, in which some are considered essential and others redundant. In general, inhibition of one or more essential PBPs results in impaired cell wall homeostasis, loss of cell integrity, and is ultimately bactericidal. Ceftazidime is a semisynthetic third-generation cephalosporin with broad activity against numerous Gram-negative and some Gram-positive bacteria. Like other β-lactam antibiotics, ceftazidime exhibits its bactericidal effect primarily through direct inhibition of specific PBPs in susceptible bacteria. _In vitro_ experiments in Gram-negative bacteria such as _Escherichia coli_, _Pseudomonas aeruginosa_, _Acinetobacter baumannii_, and _Klebsiella pneumoniae_ suggest that ceftazidime primarily binds to PBP3, with weaker binding to PBP1a/1b and PBP2 as well; although binding to other PBPs, such as PBP4, is detectable, the concentrations required are much greater than those achieved clinically. Similarly, ceftazidime showed binding to _Staphylococcus aureus_ PBP 1, 2, and 3 with a much lower affinity for PBP4. Recent data for _Mycobacterium abcessus_ suggest that ceftazidime can inhibit PonA1, PonA2, and PbpA at intermediate concentrations.

Ceftazidime has an elimination half-life of 1.5-2.8 hours in healthy subjects. As ceftazidime is primarily renally excreted, its half-life is significantly prolonged in patients with renal impairment. In patients with creatinine clearance < 12 mL/min, the half-life is prolonged to between 14 and 30 hours.

Ceftazidime administered intravenously in healthy males produced mean Cmax values of between 42 and 170 μg/mL for doses between 500 mg and 2 g, and are reached immediately following the end of the infusion period. The Cmax for 1 g of ceftazidime administered intramuscularly is attained approximately one hour following injection and is between 37 and 43 mg/L. Following intramuscular administration of 500 mg and 1 g of ceftazidime, the serum concentration remained above 4 μg/mL for six and eight hours, respectively. Ceftazidime Cmax and AUC show linear proportionality to the dose over the therapeutic range. In individuals with normal renal function, ceftazidime given intravenously every eight hours for 10 days as either 1 or 2 g doses showed no accumulation.

Approximately 80% to 90% of an intramuscular or intravenous dose of ceftazidime is excreted unchanged by the kidneys over a 24-hour period. When administered intravenously, 50% of the dose appears in the urine within two hours, with another 32% of the dose appearing by eight hours post-administration.

Ceftazidime has a volume of distribution of 15-20 L.

The mean renal clearance of ceftazidime in healthy subjects ranges from 72 to 141 mL/min while the calculated plasma clearance is approximately 115 mL/min.