Clinical Pharmacology for Azactam Injection
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 MIC90 for Neisseria sp., Haemophilus influenzae, and most genera of the Enterobacteriaceae for 8 hours (for Enterobacter sp., the 8-hour serum levels exceed the MIC for 80% of strains). For Pseudomonas aeruginosa, a single 2 g intravenous dose produces serum levels that exceed the MIC for approximately 4 to 6 hours. All of the above doses of AZACTAM result in average urine levels of aztreonam that exceed the MIC90 for the same pathogens for up to 12 hours.
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. 1-4The dosage of AZACTAM should be adjusted accordingly (see DOSAGE AND ADMINISTRATION: Renal Impairment In Adult Patients).
In patients with impaired renal function, the serum half-life of aztreonam is prolonged. (See DOSAGE AND ADMINISTRATION: Renal Impairment In Adult Patients). The serum half-life of aztreonam is only slightly prolonged in patients with hepatic impairment since the liver is a minor pathway of excretion.
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 betalactam 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 β2 -microglobulin) were used. No abnormal results were obtained.
Aztreonam achieves measurable concentrations in the following body fluids and tissues:
Table 1: Extravascular Concentrations of Aztreonam After a Single Parenteral Dosea
| Fluid or Tissue | Dose (g) | Route | Hours Post-injection | Number of Patients | Mean Concentration (mcg/mL or mcg/g) |
| Fluids |
| bile | 1 | IV | 2 | 10 | 39 |
| blister fluid | 1 | IV | 1 | 6 | 20 |
| bronchial secretion | 2 | IV | 4 | 7 | 5 |
| cerebrospinal fluid (inflamed meninges) | 2 | IV | 0.9-4.3 | 16 | 3 |
| pericardial fluid | 2 | IV | 1 | 6 | 33 |
| pleural fluid | 2 | IV | 1.1-3.0 | 3 | 51 |
| synovial fluid | 2 | IV | 0.8-1.9 | 11 | 83 |
| Tissues |
| atrial appendage | 2 | IV | 0.9-1.6 | 12 | 22 |
| endometrium | 2 | IV | 0.7-1.9 | 4 | 9 |
| fallopian tube | 2 | IV | 0.7-1.9 | 8 | 12 |
| fat | 2 | IV | 1.3-2.0 | 10 | 5 |
| femur | 2 | IV | 1.0-2.1 | 15 | 16 |
| gallbladder | 2 | IV | 0.8-1.3 | 4 | 23 |
| kidney | 2 | IV | 2.4-5.6 | 5 | 67 |
| large intestine | 2 | IV | 0.8-1.9 | 9 | 12 |
| liver | 2 | IV | 0.9-2.0 | 6 | 47 |
| lung | 2 | IV | 1.2-2.1 | 6 | 22 |
| myometrium | 2 | IV | 0.7-1.9 | 9 | 11 |
| ovary | 2 | IV | 0.7-1.9 | 7 | 13 |
| prostate | 1 | IM | 0.8-3.0 | 8 | 8 |
| skeletal muscle | 2 | IV | 0.3-0.7 | 6 | 16 |
| skin | 2 | IV | 0.0-1.0 | 8 | 25 |
| sternum | 2 | IV | 1 | 6 | 6 |
| a Tissue penetration is regarded as essential to therapeutic efficacy, but specific tissue levels have not been correlated with specific therapeutic effects. |
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 in vitro against most strains of P. aeruginosa, many strains of Enterobacteriaceae, and other Gram-negative aerobic bacilli.
Aztreonam has been shown to be active against most strains of the following microorganisms, both in vitro and in clinical infections as described in the INDICATIONS AND USAGE5 section.
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 in vitro data are available, but their clinical significance is unknown. At least 90% of the following microorganisms exhibit an in vitro minimum inhibitory concentration (MIC) less than or equal to the susceptible breakpoint for aztreonam. However, the efficacy of aztreonam in treating clinical infections due to these microorganisms has not been established in adequate and well-controlled clinical trials.
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 in vitro against most strains of P. aeruginosa, many strains of Enterobacteriaceae, and other Gram-negative aerobic bacilli.
Alterations of the anaerobic intestinal flora by broad-spectrum antibiotics may decrease colonization resistance, thus permitting overgrowth of potential pathogens, eg, Candida and Clostridium species. Aztreonam has little effect on the anaerobic intestinal microflora in in vitro studies. Clostridium difficile and its cytotoxin were not found in animal models following administration of aztreonam. (See ADVERSE REACTIONS: Gastrointestinal.)
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.
Clinical Studies
A total of 612 pediatric patients aged 1 month to 12 years were enrolled in uncontrolled clinical trials of aztreonam in the treatment of serious Gram-negative infections, including urinary tract, lower respiratory tract, skin and skin-structure, and intra-abdominal infections.
Preparation Of Parenteral Solutions
General
Upon the addition of the diluent to the container, contents should be shaken immediately and vigorously Constituted solutions are not for multiple-dose use; should the entire volume in the container not be used for a single dose, the unused solution must be discarded.
Depending upon the concentration of aztreonam and diluent used, constituted AZACTAM yields a colorless to light straw yellow solution which may develop a slight pink tint on standing (potency is not affected). Parenteral drug products should be inspected visually for particulate matter and discoloration whenever solution and container permit.
Admixtures With Other Antibiotics
Intravenous infusion solutions of AZACTAM not exceeding 2% w/v prepared with Sodium Chloride Injection, USP 0.9% or Dextrose Injection, USP 5%, to which clindamycin phosphate, gentamicin sulfate, tobramycin sulfate, or cefazolin sodium have been added at concentrations usually used clinically, are stable for up to 48 hours at room temperature or 7 days under refrigeration. Ampicillin sodium admixtures with aztreonam in Sodium Chloride Injection, USP 0.9% are stable for 24 hours at room temperature and 48 hours under refrigeration; stability in Dextrose Injection, USP 5% is 2 hours at room temperature and 8 hours under refrigeration.
Aztreonam-cloxacillin sodium and aztreonam-vancomycin hydrochloride admixtures are stable in Dianeal 137 (Peritoneal Dialysis Solution) with 4.25% Dextrose for up to 24 hours at room temperature.
Aztreonam is incompatible with nafcillin sodium, cephradine, and metronidazole.
Other admixtures are not recommended since compatibility data are not available.
Intravenous Solutions
For Bolus Injection
The contents of an AZACTAM 15 mL capacity vial should be constituted with 6 to 10 mL Sterile Water for Injection, USP.
For Infusion
If the contents of a 15 mL capacity vial are to be transferred to an appropriate infusion solution, each gram of aztreonam should be initially constituted with at least 3 mL Sterile Water for Injection, USP. Further dilution may be obtained with one of the following intravenous infusion solutions:
Sodium Chloride Injection, USP, 0.9%Ringer’s Injection, USPLactated Ringer’s Injection, USP Dextrose Injection, USP, 5% or 10% Dextrose and Sodium Chloride Injection, USP, 5%:0.9%, 5%:0.45%, or 5%:0.2% Sodium Lactate Injection, USP (M/6 Sodium Lactate) Ionosol® B and 5% Dextrose Isolyte® EIsolyte® E with 5% Dextrose Isolyte® M with 5% Dextrose Normosol® -R Normosol -R and 5% Dextrose Normosol -M and 5% Dextrose Mannitol Injection, USP, 5% or 10% Lactated Ringer’s and 5% Dextrose Injection Plasma-Lyte M and 5% Dextrose
Intramuscular Solutions
The contents of an AZACTAM 15 mL capacity vial should be constituted with at least 3 mL of an appropriate diluent per gram aztreonam. The following diluents may be used:
Sterile Water for Injection, USP
Sterile Bacteriostatic Water for Injection, USP (with benzyl alcohol or with methyl- and propylparabens)
Sodium Chloride Injection, USP, 0.9%
Bacteriostatic Sodium Chloride Injection, USP (with benzyl alcohol)
Stability Of Intravenous And Intramuscular Solutions
AZACTAM solutions for intravenous infusion at concentrations not exceeding 2% w/v must be used within 48 hours following constitution if kept at controlled room temperature (59°F-86°F/15°C-30°C) or within 7 days if refrigerated (36°F-46°F/2°C-8°C).
AZACTAM solutions at concentrations exceeding 2% w/v, except those prepared with Sterile Water for Injection, USP or Sodium Chloride Injection, USP, should be used promptly after preparation; the 2 excepted solutions must be used within 48 hours if stored at controlled room temperature or within 7 days if refrigerated.
Intravenous Administration
Bolus Injection
A bolus injection may be used to initiate therapy. The dose should be slowly injected directly into a vein, or the tubing of a suitable administration set, over a period of 3 to 5 minutes (see next paragraph regarding flushing of tubing).
Infusion
With any intermittent infusion of aztreonam and another drug with which it is not pharmaceutically compatible, the common delivery tube should be flushed before and after delivery of aztreonam with any appropriate infusion solution compatible with both drug solutions; the drugs should not be delivered simultaneously. Any AZACTAM infusion should be completed within a 20- to 60-minute period. With use of a Y-type administration set, careful attention should be given to the calculated volume of aztreonam solution required so that the entire dose will be infused. A volume control administration set may be used to deliver an initial dilution of AZACTAM (see Preparation Of Parenteral Solutions: Intravenous Solutions: For Infusion) into a compatible infusion solution during administration; in this case, the final dilution of aztreonam should provide a concentration not exceeding 2% w/v.
Intramuscular Administration
The dose should be given by deep injection into a large muscle mass (such as the upper outer quadrant of the gluteus maximus or lateral part of the thigh). Aztreonam is well tolerated and should not be admixed with any local anesthetic agent.