Azactam (Aztreonam)
Monobactam antibiotic for serious Gram-negative bacterial infections
Quick Facts About Azactam
Key Takeaways About Azactam
- Gram-negative specialist: Aztreonam targets only aerobic Gram-negative bacteria, including Pseudomonas aeruginosa, and has no activity against Gram-positive organisms or anaerobes
- Safe in penicillin allergy: Unlike other beta-lactams, aztreonam has a monocyclic ring structure with minimal cross-reactivity to penicillins and cephalosporins (except ceftazidime)
- Hospital-only administration: Given only by IV infusion or IM injection in clinical settings; not available in oral form
- Dose adjustment in renal impairment: Reduce dose by 50% when creatinine clearance falls below 30 mL/min; supplement after hemodialysis
- Unique beta-lactam: The only commercially available monobactam antibiotic, making it a distinctive and irreplaceable option in certain clinical scenarios
What Is Azactam and What Is It Used For?
Azactam (aztreonam) is the only commercially available monobactam antibiotic, approved for treating serious infections caused by susceptible aerobic Gram-negative bacteria. It is used for urinary tract infections, lower respiratory tract infections, bloodstream infections (septicemia), skin infections, intra-abdominal infections, and gynecological infections.
Aztreonam belongs to the monobactam class of beta-lactam antibiotics. Unlike penicillins, cephalosporins, and carbapenems, which have a bicyclic or fused ring structure, aztreonam has a unique monocyclic (single-ring) beta-lactam nucleus. This distinctive chemical structure gives it a narrow but clinically important spectrum of activity exclusively against aerobic Gram-negative bacteria, while offering the significant advantage of minimal cross-allergenicity with other beta-lactam antibiotics.
The drug was originally isolated from Chromobacterium violaceum, a bacterium found in soil and water. It was first approved by the United States Food and Drug Administration (FDA) in 1986 and has since become an established part of the antimicrobial armamentarium worldwide. Aztreonam is marketed under the brand name Azactam and is available as a powder for reconstitution for intravenous (IV) or intramuscular (IM) injection.
Azactam is indicated for the treatment of infections caused by susceptible strains of designated microorganisms in the following clinical conditions:
- Urinary tract infections (UTIs): Including pyelonephritis and cystitis caused by E. coli, Klebsiella pneumoniae, Proteus mirabilis, Pseudomonas aeruginosa, Enterobacter cloacae, Klebsiella oxytoca, Citrobacter species, and Serratia marcescens
- Lower respiratory tract infections: Including pneumonia and bronchitis caused by E. coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Haemophilus influenzae, Proteus mirabilis, Enterobacter species, and Serratia marcescens
- Septicemia (bloodstream infections): Caused by E. coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Proteus mirabilis, Serratia marcescens, and Enterobacter species
- Skin and skin-structure infections: Including postoperative wounds, ulcers, and burns caused by E. coli, Proteus mirabilis, Serratia marcescens, Enterobacter species, Pseudomonas aeruginosa, Klebsiella pneumoniae, and Citrobacter species
- Intra-abdominal infections: Including peritonitis caused by E. coli, Klebsiella species, Enterobacter species, Pseudomonas aeruginosa, Citrobacter species, and Serratia species. These infections are typically treated in combination with an agent active against anaerobes
- Gynecological infections: Including endometritis and pelvic cellulitis caused by E. coli, Klebsiella pneumoniae, Enterobacter species, and Proteus mirabilis
Aztreonam works by binding to penicillin-binding protein 3 (PBP-3) in susceptible Gram-negative organisms. PBP-3 is essential for bacterial cell division (septation). By inhibiting this protein, aztreonam prevents the formation of the bacterial cell wall septum, resulting in the formation of long, filamentous bacterial cells that eventually undergo lysis and death. It is highly resistant to hydrolysis by most beta-lactamases, including those produced by Gram-negative bacteria.
Aztreonam has no clinically useful activity against Gram-positive organisms (such as Staphylococcus aureus or Streptococcus pneumoniae) or anaerobes (such as Bacteroides fragilis). For this reason, it is frequently combined with other antibiotics when treating polymicrobial infections. Common combination partners include metronidazole or clindamycin for anaerobic coverage, and vancomycin or linezolid for Gram-positive coverage.
An inhaled formulation of aztreonam (marketed as Cayston) is also available for the management of chronic pulmonary infections due to Pseudomonas aeruginosa in patients with cystic fibrosis. This formulation is delivered via a nebulizer and represents a separate product with distinct prescribing information from the parenteral Azactam formulation discussed in this article.
What Should You Know Before Taking Azactam?
Before receiving Azactam, inform your healthcare provider about any allergies to antibiotics, kidney disease, liver disease, or if you are pregnant or breastfeeding. While aztreonam has low cross-reactivity with other beta-lactams, caution is warranted if you have a history of severe allergic reactions to ceftazidime.
Contraindications
Azactam is contraindicated in patients with a known hypersensitivity to aztreonam or any component of the formulation. While cross-reactivity with other beta-lactam antibiotics is rare, there is a recognized potential for cross-reactivity between aztreonam and ceftazidime because these two drugs share an identical aminothiazolyl side chain. Patients with a documented IgE-mediated allergy to ceftazidime should be treated with aztreonam only with caution and appropriate monitoring.
Unlike other beta-lactam antibiotics, aztreonam does not generally cross-react with penicillins or most cephalosporins. This is due to its monocyclic structure, which differs fundamentally from the bicyclic ring systems found in penicillins (thiazolidine + beta-lactam) and cephalosporins (dihydrothiazine + beta-lactam). Multiple studies and decades of clinical experience have confirmed that aztreonam can be safely administered to the majority of patients with IgE-mediated penicillin allergy.
Warnings and Precautions
Clostridioides difficile-associated diarrhea (CDAD) has been reported with the use of nearly all antibacterial agents, including aztreonam, and may range from mild diarrhea to fatal colitis. If CDAD is suspected or confirmed, ongoing antibiotic use not directed against C. difficile should be discontinued. Appropriate measures including fluid and electrolyte management, protein supplementation, and treatment with an antibacterial drug effective against C. difficile should be instituted.
- Renal impairment: Since aztreonam is primarily excreted by the kidneys, dose adjustment is necessary in patients with significant renal impairment (creatinine clearance ≤ 30 mL/min). Serum aztreonam levels should be monitored in patients with severe renal failure
- Hepatic impairment: Transient elevations in hepatic transaminases (ALT, AST) have been observed. Use with caution in patients with pre-existing liver disease and monitor hepatic function during prolonged therapy
- Superinfection: As with all antibiotics, prolonged use may result in overgrowth of non-susceptible organisms, including fungi. Careful observation of the patient is essential; if superinfection occurs, appropriate therapy should be initiated
- Seizures: Rare cases of seizures have been reported, particularly in patients with renal impairment receiving high doses without appropriate dose adjustment, or in patients with underlying CNS disorders
- Toxic epidermal necrolysis (TEN): Rare cases of TEN have been reported in patients undergoing bone marrow transplant who were receiving multiple medications. A causal relationship to aztreonam is uncertain but the possibility should be considered
Pregnancy and Breastfeeding
Aztreonam crosses the placenta and enters fetal circulation. Animal reproduction studies have not demonstrated evidence of embryotoxicity, fetotoxicity, or teratogenicity. However, there are no adequate and well-controlled studies in pregnant women. Aztreonam should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus. According to the FDA pregnancy categorization system (prior to its removal in 2015), aztreonam was classified as Pregnancy Category B.
Aztreonam is excreted in human breast milk in low concentrations (less than 1% of the maternal serum concentration). Although this represents a very small exposure to the nursing infant, caution should be exercised when aztreonam is administered to a breastfeeding woman. The low oral bioavailability of aztreonam means that any drug present in breast milk would be poorly absorbed by the infant, further reducing the risk of adverse effects. The American Academy of Pediatrics has generally considered aztreonam compatible with breastfeeding.
How Does Azactam Interact with Other Drugs?
Azactam has relatively few significant drug interactions. Key interactions include antagonism with cefoxitin and chloramphenicol (which can reduce aztreonam's effectiveness), synergism with aminoglycosides, and increased serum levels when co-administered with probenecid or furosemide.
Although aztreonam has fewer drug interactions than many other antibiotics, certain combinations require clinical awareness. The interactions can be categorized by their clinical significance and mechanism. Aztreonam is neither a significant inducer nor inhibitor of cytochrome P450 enzymes, which limits its potential for metabolic drug interactions.
| Interacting Drug | Effect | Severity | Clinical Recommendation |
|---|---|---|---|
| Cefoxitin | Antagonism: cefoxitin may induce beta-lactamases that can hydrolyze aztreonam in vitro | Major | Avoid concurrent use. If combination needed, administer sequentially rather than simultaneously |
| Chloramphenicol | Antagonism: chloramphenicol may antagonize the bactericidal activity of aztreonam | Major | Avoid concurrent use. Bacteriostatic agents like chloramphenicol can counteract bactericidal beta-lactams |
| Imipenem | Potential antagonism in vitro against some Enterobacteriaceae; imipenem-induced beta-lactamases may inactivate aztreonam | Moderate | Use combination with caution; may be beneficial against some organisms but antagonistic against others. Check susceptibility data |
| Aminoglycosides (gentamicin, tobramycin, amikacin) | Synergism: enhanced bactericidal activity against many Gram-negative organisms including Pseudomonas | Beneficial | Commonly used in combination for serious Pseudomonas infections. Administer separately (do not mix in same infusion line) |
| Probenecid | Increased aztreonam serum levels by inhibiting renal tubular secretion | Minor | No dose adjustment generally required; the increase is modest. Monitor for increased side effects with prolonged co-administration |
| Furosemide | May slightly increase aztreonam serum concentrations through competition for renal tubular secretion | Minor | No dose adjustment required in most patients. Be aware of increased levels in patients with renal impairment |
| Oral anticoagulants (warfarin) | Rare reports of altered INR; mechanism unclear | Minor | Monitor INR closely when initiating or discontinuing aztreonam in patients on warfarin |
Synergistic Combinations
In clinical practice, aztreonam is frequently combined with other antibiotics to broaden the spectrum of coverage. The most important synergistic combination is with aminoglycosides (such as gentamicin, tobramycin, or amikacin) for enhanced killing of Gram-negative organisms, particularly Pseudomonas aeruginosa. In vitro studies have demonstrated that the aztreonam-aminoglycoside combination produces synergistic bactericidal activity against 50-70% of Pseudomonas aeruginosa isolates.
Aztreonam is also commonly paired with metronidazole or clindamycin to provide anaerobic coverage in intra-abdominal infections, and with vancomycin or daptomycin for Gram-positive coverage in polymicrobial infections. These combinations take advantage of aztreonam's exclusive Gram-negative activity while filling the gaps in its spectrum with complementary agents.
Laboratory Test Interactions
Aztreonam may cause a false-positive reaction for urinary glucose when using copper sulfate-based tests (such as Clinitest). Glucose oxidase methods (such as Clinistix or Diastix) are not affected and should be used for monitoring urinary glucose in patients receiving aztreonam. Additionally, aztreonam may cause a positive direct Coombs test, though clinically significant hemolytic anemia is extremely rare.
What Is the Correct Dosage of Azactam?
The usual adult dosage of Azactam ranges from 500 mg to 2 g administered every 6 to 12 hours, depending on the type and severity of infection. The maximum recommended daily dose is 8 g. Dose reduction is required in patients with significant renal impairment.
Aztreonam dosing is determined by the type of infection being treated, its severity, and the patient's renal function. The drug can be administered intravenously (by bolus injection over 3-5 minutes or by infusion over 20-60 minutes) or intramuscularly. For severe systemic infections, the IV route is preferred to achieve reliable and consistent serum levels.
Adults
| Infection Type | Dose | Frequency | Notes |
|---|---|---|---|
| Urinary tract infection (uncomplicated) | 500 mg or 1 g | Every 8-12 hours | IM or IV |
| Urinary tract infection (complicated) | 1 g or 2 g | Every 8-12 hours | IV preferred for complicated cases |
| Moderately severe infections (skin, respiratory) | 1 g or 2 g | Every 8-12 hours | IV or IM |
| Severe systemic infections (septicemia) | 2 g | Every 6-8 hours | IV only. Max 8 g/day |
| Pseudomonas aeruginosa infections | 2 g | Every 6-8 hours | IV. Often combined with aminoglycoside |
Children
For children aged 9 months and older, the recommended dose is 30 mg/kg body weight administered intravenously every 6 to 8 hours. For severe infections, a dose of up to 50 mg/kg every 6 to 8 hours may be used. The maximum daily dose should not exceed 120 mg/kg/day (up to the adult maximum of 8 g/day, whichever is lower).
Safety and efficacy in neonates (birth to 9 months) have not been fully established through well-controlled clinical trials, although aztreonam has been used in neonatal intensive care settings under specialist guidance. Published case series and pharmacokinetic studies in neonates suggest dosing of 30 mg/kg every 8-12 hours depending on gestational age and postnatal age, but these represent off-label use and should be guided by specialist infectious disease or neonatal pharmacy expertise.
Elderly Patients
No specific dose adjustment is required for elderly patients based on age alone. However, since renal function commonly declines with age, creatinine clearance should be estimated and dosing adjusted accordingly if impairment is detected. Elderly patients are also at increased risk for Clostridioides difficile-associated diarrhea and should be monitored closely during and after antibiotic therapy.
Renal Dose Adjustment
Dose Adjustment Based on Creatinine Clearance
- CrCl > 30 mL/min: No dose adjustment required
- CrCl 10-30 mL/min: Give the usual initial loading dose, then reduce the maintenance dose by 50% (i.e., use half the standard dose at the usual interval)
- CrCl < 10 mL/min: Give the usual initial loading dose, then reduce the maintenance dose to 25% of normal
- Hemodialysis patients: Aztreonam is partially removed by hemodialysis. A supplemental dose equal to one-eighth of the initial dose should be given after each hemodialysis session
- Peritoneal dialysis: Aztreonam is not significantly removed by peritoneal dialysis. Dose according to degree of renal impairment
Missed Dose
Because Azactam is administered in a hospital setting by healthcare professionals, missed doses are uncommon. However, if a dose is inadvertently missed, it should be administered as soon as possible. If it is close to the time of the next scheduled dose, the missed dose should be skipped and the regular dosing schedule resumed. Do not double the dose to make up for a missed one. Maintaining consistent blood levels is important for the efficacy of aztreonam, so any deviations from the dosing schedule should be documented and communicated to the treating physician.
Overdose
There is limited clinical experience with aztreonam overdose. In healthy volunteers, single IV doses of up to 8 g have been administered without clinically significant adverse effects. In the event of overdose, supportive care and monitoring of renal and hepatic function are recommended. Aztreonam serum levels can be reduced by hemodialysis and/or peritoneal dialysis. Symptoms of overdose might include nausea, vomiting, diarrhea, and seizures (particularly in patients with impaired renal function). There is no specific antidote for aztreonam overdose.
What Are the Side Effects of Azactam?
Azactam is generally well tolerated. The most common side effects include injection site reactions (pain, phlebitis), diarrhea, nausea, and rash. Serious but rare side effects include Clostridioides difficile colitis, seizures, and anaphylaxis. Most adverse reactions are mild and transient.
Aztreonam has a favorable safety profile compared to many other parenteral antibiotics. Clinical trials and post-marketing surveillance have identified the following adverse effects organized by frequency category. The data below are compiled from clinical trials involving over 8,000 patients and post-marketing reports.
Common
- Injection site reactions (pain, swelling, erythema at IM site; phlebitis/thrombophlebitis at IV site)
- Diarrhea
- Nausea and/or vomiting
- Skin rash (maculopapular or urticarial)
- Elevated hepatic transaminases (ALT, AST) - usually transient and asymptomatic
Uncommon
- Abdominal cramps
- Altered taste (dysgeusia)
- Oral ulceration or mouth soreness
- Pruritus (itching)
- Eosinophilia
- Thrombocytopenia (low platelet count)
- Leukopenia or neutropenia (low white blood cell count)
- Transient elevation of serum creatinine
- Headache
- Dizziness
- Vaginal candidiasis
Rare
- Clostridioides difficile-associated diarrhea (CDAD) / pseudomembranous colitis
- Anaphylaxis or anaphylactoid reactions
- Seizures (particularly in patients with renal impairment or CNS disorders)
- Toxic epidermal necrolysis (TEN) - reported primarily in bone marrow transplant patients
- Pancytopenia
- Prolongation of prothrombin time and partial thromboplastin time
- Hepatitis or jaundice
- Erythema multiforme
- Exfoliative dermatitis
- Positive direct Coombs test
- Muscular aches (myalgia)
- Tinnitus or diplopia (double vision)
Seek immediate medical attention if you experience signs of a severe allergic reaction (difficulty breathing, facial or throat swelling, severe rash), persistent or bloody diarrhea (which may indicate C. difficile infection), yellowing of the skin or eyes (jaundice), unusual bleeding or bruising, or seizures. Although serious side effects are rare with aztreonam, early recognition and management are important.
In clinical trials, the overall incidence of adverse reactions leading to discontinuation of therapy was approximately 1.6%, which is lower than that of many comparable antibiotics. Laboratory abnormalities, particularly transient elevations of hepatic enzymes, are among the most frequently reported findings but rarely require discontinuation of the drug. Hematologic changes such as eosinophilia and thrombocytopenia are typically mild and reversible upon discontinuation.
Post-marketing experience has not identified any new safety signals beyond those observed in clinical trials. The long track record of aztreonam use since its approval in 1986 provides substantial reassurance regarding its safety profile, particularly in comparison to broader-spectrum agents that may carry higher risks of certain adverse effects such as Clostridioides difficile infection or fungal superinfection.
How Should You Store Azactam?
Azactam powder for injection should be stored at controlled room temperature (15-30°C / 59-86°F) and protected from light. After reconstitution, solutions are stable for 48 hours at room temperature or 7 days when refrigerated (2-8°C).
Proper storage of Azactam is essential to maintain the drug's potency and safety. The unreconstituted (dry powder) vials should be stored at controlled room temperature between 15°C and 30°C (59°F to 86°F). The vials do not need to be refrigerated before reconstitution. They should be protected from excessive light exposure, although brief exposure to light during normal handling does not affect potency.
After reconstitution, the stability of the solution depends on the diluent used and storage conditions:
- Reconstituted for IM injection: Use within 48 hours when stored at room temperature (25°C), or within 7 days when refrigerated (2-8°C)
- Reconstituted for IV injection/infusion: Stability varies by diluent. Solutions in 0.9% sodium chloride or 5% dextrose are stable for up to 48 hours at room temperature or 7 days when refrigerated
- Frozen solutions: Reconstituted solutions may be frozen at -20°C for up to 3 months. Thawed solutions should not be refrozen and should be used within 24 hours of thawing at room temperature or within 72 hours if thawed under refrigeration
Visual inspection of the reconstituted solution should be performed before administration. The solution should be clear and colorless to light straw yellow. Solutions that are cloudy, contain particulate matter, or are deeply colored should be discarded. Do not use the product after the expiration date printed on the vial or packaging.
What Does Azactam Contain?
Each vial of Azactam contains aztreonam as the active ingredient (available in 500 mg, 1 g, or 2 g strengths) along with approximately 780 mg of L-arginine per gram of aztreonam as a buffering agent. No other excipients are present in the formulation.
Azactam has a remarkably simple formulation containing only two components:
- Active ingredient: Aztreonam (C13H17N5O8S2) is a synthetic monocyclic beta-lactam antibiotic. Its molecular weight is 435.43 daltons. Aztreonam is a white to slightly yellowish crystalline powder that is sparingly soluble in water
- Buffer/excipient: L-arginine is included at approximately 780 mg per gram of aztreonam. It serves as a buffering agent to maintain the pH of the reconstituted solution at approximately 4.5-7.5. L-arginine is a naturally occurring amino acid and is generally well tolerated
The absence of preservatives in the formulation means that reconstituted solutions should be used within the recommended stability timeframe. Aztreonam for injection contains no sodium, making it suitable for patients on sodium-restricted diets. The pH of the reconstituted IV solution ranges from approximately 4.5 to 7.5 depending on the concentration and diluent used.
Aztreonam is structurally related to the naturally occurring monobactam SQ 26,180, which was originally isolated from the bacterium Chromobacterium violaceum. The commercial product is manufactured entirely by chemical synthesis rather than fermentation. The drug's monocyclic beta-lactam ring, combined with its sulfonic acid group and aminothiazolyl oxime side chain, gives it the unique properties that distinguish it from all other beta-lactam antibiotics: exclusive Gram-negative activity, resistance to many beta-lactamases, and minimal cross-allergenicity with penicillins and cephalosporins.
Frequently Asked Questions About Azactam
Azactam (aztreonam) is generally considered safe for patients with IgE-mediated penicillin allergy. Its unique monocyclic beta-lactam structure differs significantly from the bicyclic ring of penicillins, resulting in very low cross-reactivity. Clinical experience with thousands of penicillin-allergic patients has confirmed the safety of this approach. However, if you have a history of severe allergic reactions to ceftazidime specifically, extra caution is warranted because aztreonam and ceftazidime share an identical side chain. Always inform your healthcare team about all drug allergies before receiving any antibiotic.
No, Azactam is not available in oral form. Aztreonam has very poor oral bioavailability (less than 1%) because it is poorly absorbed from the gastrointestinal tract. It must be administered by intravenous (IV) infusion or intramuscular (IM) injection in a healthcare setting. An inhaled formulation (Cayston) exists for cystic fibrosis patients with chronic Pseudomonas lung infections, but this is a separate product. There is currently no oral monobactam antibiotic available for clinical use.
No, Azactam has no clinically useful activity against Gram-positive bacteria, including methicillin-resistant Staphylococcus aureus (MRSA), methicillin-susceptible S. aureus (MSSA), Streptococcus species, or Enterococcus species. Its spectrum is limited exclusively to aerobic Gram-negative bacteria. If you have a mixed infection involving both Gram-negative and Gram-positive organisms, your doctor will prescribe additional antibiotics (such as vancomycin, linezolid, or daptomycin) to cover the Gram-positive component.
The duration of Azactam therapy depends on the type and severity of infection. Uncomplicated urinary tract infections may require only 3-5 days of treatment, while more serious infections such as pneumonia or septicemia typically require 7-14 days. Intra-abdominal infections and bone/joint infections may require even longer courses. Your doctor will determine the appropriate duration based on your clinical response, culture results, and the nature of the infection. It is important to complete the full prescribed course even if you begin feeling better.
Like all antibiotics, inappropriate or excessive use of Azactam can contribute to the development of antibiotic resistance. However, aztreonam has some unique properties that may limit its impact on resistance. Because it has no activity against Gram-positive bacteria or anaerobes, it exerts less selective pressure on normal gut flora compared to broader-spectrum antibiotics. This may result in a lower risk of selecting for resistant organisms or causing Clostridioides difficile overgrowth. Nonetheless, aztreonam should only be used when clinically indicated and guided by susceptibility testing whenever possible.
Both Azactam and Cayston contain aztreonam as the active ingredient, but they are different formulations designed for different routes of administration. Azactam is a parenteral formulation given by IV or IM injection for systemic infections. Cayston (aztreonam lysine for inhalation) is a formulation specifically designed for nebulized delivery directly to the lungs and is approved for the treatment of chronic pulmonary Pseudomonas aeruginosa infections in cystic fibrosis patients aged 7 years and older. The two products are not interchangeable and have separate prescribing information.
References and Sources
This article is based on the following evidence-based sources:
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- Infectious Diseases Society of America (IDSA). Practice Guidelines for the Diagnosis and Management of Skin and Soft Tissue Infections: 2014 Update. Clin Infect Dis. 2014;59(2):e10-e52.
- Sykes RB, Bonner DP. Discovery and development of monobactams. Rev Infect Dis. 1985;7 Suppl 4:S579-S593.
- Solomkin JS, Mazuski JE, Bradley JS, et al. Diagnosis and Management of Complicated Intra-abdominal Infection in Adults and Children: Guidelines by the Surgical Infection Society and the Infectious Diseases Society of America. Clin Infect Dis. 2010;50(2):133-164.
About Our Medical Editorial Team
This article has been written and reviewed by the iMedic Medical Editorial Team, which includes board-certified specialists in infectious diseases, clinical pharmacology, and internal medicine.
Written by specialists in infectious diseases and antimicrobial pharmacology with expertise in beta-lactam antibiotics and antimicrobial stewardship.
Reviewed by the iMedic Medical Review Board according to international guidelines (WHO, EMA, FDA, IDSA). Evidence level: 1A.
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