Single 30-minute intravenous infusions of 500 mg, 1 g, and 2 g doses of AZACTAM in healthy subjects produced aztreonam peak serum levels of 54 mcg/mL, 90 mcg/mL, and 204 mcg/mL, respectively, immediately after administration; at 8 hours, serum levels were 1 mcg/mL, 3 mcg/mL, and 6 mcg/mL, respectively (Figure 1). Single 3-minute intravenous injections of the same doses resulted in serum levels of 58 mcg/mL, 125 mcg/mL, and 242 mcg/mL at 5 minutes following completion of injection.
Serum concentrations of aztreonam in healthy subjects following completion of single intramuscular injections of 500 mg and 1 g doses are depicted in Figure 1; maximum serum concentrations occur at about 1 hour. After identical single intravenous or intramuscular doses of AZACTAM, the serum concentrations of aztreonam are comparable at 1 hour (1.5 hours from start of intravenous infusion) with similar slopes of serum concentrations thereafter.
FIGURE 1

The serum levels of aztreonam following single 500 mg or 1 g (intramuscular or intravenous) or 2 g (intravenous) doses of AZACTAM exceed the MIC
When aztreonam pharmacokinetics were assessed for adult and pediatric patients, they were found to be comparable (down to 9 months old). The serum half-life of aztreonam averaged 1.7 hours (1.5-2.0) in subjects with normal renal function, independent of the dose and route of administration. In healthy subjects, based on a 70 kg person, the serum clearance was 91 mL/min and renal clearance was 56 mL/min; the apparent mean volume of distribution at steady-state averaged 12.6 liters, approximately equivalent to extracellular fluid volume.
In elderly patients, the mean serum half-life of aztreonam increased and the renal clearance decreased, consistent with the age-related decrease in creatinine clearance. The dosage of AZACTAM should be adjusted accordingly (see
In patients with impaired renal function, the serum half-life of aztreonam is prolonged. (See
Average urine concentrations of aztreonam were approximately 1100 mcg/mL, 3500 mcg/mL, and 6600 mcg/mL within the first 2 hours following single 500 mg, 1 g, and 2 g intravenous doses of AZACTAM (30-minute infusions), respectively. The range of average concentrations for aztreonam in the 8- to 12-hour urine specimens in these studies was 25 to 120 mcg/mL. After intramuscular injection of single 500 mg and 1 g doses of AZACTAM, urinary levels were approximately 500 mcg/mL and 1200 mcg/mL, respectively, within the first 2 hours, declining to 180 mcg/mL and 470 mcg/mL in the 6- to 8-hour specimens. In healthy subjects, aztreonam is excreted in the urine about equally by active tubular secretion and glomerular filtration. Approximately 60% to 70% of an intravenous or intramuscular dose was recovered in the urine by 8 hours. Urinary excretion of a single parenteral dose was essentially complete by 12 hours after injection. About 12% of a single intravenous radiolabeled dose was recovered in the feces. Unchanged aztreonam and the inactive beta-lactam ring hydrolysis product of aztreonam were present in feces and urine.
Intravenous or intramuscular administration of a single 500 mg or 1 g dose of AZACTAM every 8 hours for 7 days to healthy subjects produced no apparent accumulation of aztreonam or modification of its disposition characteristics; serum protein binding averaged 56% and was independent of dose. An average of about 6% of a 1 g intramuscular dose was excreted as a microbiologically inactive open beta-lactam ring hydrolysis product (serum half-life approximately 26 hours) of aztreonam in the 0‑ to 8-hour urine collection on the last day of multiple dosing.
Renal function was monitored in healthy subjects given aztreonam; standard tests (serum creatinine, creatinine clearance, BUN, urinalysis, and total urinary protein excretion) as well as special tests (excretion of N-acetyl-β-glucosaminidase, alanine aminopeptidase, and β
Aztreonam achieves measurable concentrations in the following body fluids and tissues:
The concentration of aztreonam in saliva at 30 minutes after a single 1 g intravenous dose (9 patients) was 0.2 mcg/mL; in human milk at 2 hours after a single 1 g intravenous dose (6 patients), 0.2 mcg/mL, and at 6 hours after a single 1 g intramuscular dose (6 patients), 0.3 mcg/mL; in amniotic fluid at 6 to 8 hours after a single 1 g intravenous dose (5 patients), 2 mcg/mL. The concentration of aztreonam in peritoneal fluid obtained 1 to 6 hours after multiple 2 g intravenous doses ranged between 12 mcg/mL and 90 mcg/mL in 7 of 8 patients studied.
Aztreonam given intravenously rapidly reaches therapeutic concentrations in peritoneal dialysis fluid; conversely, aztreonam given intraperitoneally in dialysis fluid rapidly produces therapeutic serum levels.
Concomitant administration of probenecid or furosemide and aztreonam causes clinically insignificant increases in the serum levels of aztreonam. Single-dose intravenous pharmacokinetic studies have not shown any significant interaction between aztreonam and concomitantly administered gentamicin, nafcillin sodium, cephradine, clindamycin, or metronidazole. No reports of disulfiram-like reactions with alcohol ingestion have been noted; this is not unexpected since aztreonam does not contain a methyl-tetrazole side chain.
Microbiology
Mechanism of Action
Aztreonam is a bactericidal agent that acts by inhibition of bacterial cell wall synthesis. Aztreonam has activity in the presence of some beta-lactamases, both penicillinases and cephalosporinases, of Gram-negative and Gram-positive bacteria.
Mechanism of Resistance
Resistance to aztreonam is primarily through hydrolysis by beta-lactamase, alteration of penicillin-binding proteins (PBPs), and decreased permeability.
Interaction with Other Antimicrobials
Aztreonam and aminoglycosides have been shown to be synergistic
Aztreonam has been shown to be active against most strains of the following microorganisms, both
Aerobic Gram-negative microorganisms:
Citrobacter species
Enterobacter species
Escherichia coli
Haemophilus influenzae (including ampicillin-resistant and other penicillinase-producing strains)
Klebsiella oxytoca
Klebsiella pneumoniae
Proteus mirabilis
Pseudomonas aeruginosa
Serratia species
The following
Aerobic Gram-negative microorganisms:
Aeromonas hydrophila
Morganella morganii
Neisseria gonorrhoeae (including penicillinase-producing strains)
Pasteurella multocida Proteus vulgaris
Providencia stuartii
Providencia rettgeri
Yersinia enterocolitica
Aztreonam and aminoglycosides have been shown to be synergistic
Alterations of the anaerobic intestinal flora by broad-spectrum antibiotics may decrease colonization resistance, thus permitting overgrowth of potential pathogens, eg,
Susceptibility Testing
For specific information regarding susceptibility test interpretive criteria and associated test methods and quality control standards recognized by FDA for this drug, please see: https://www.fda.gov/STIC.