Hypersensitivity aztreonam

Aztreonam may be used as a substitute for an aminoglycoside in the treatment of infections caused by susceptible gram-negative organisms. Most of the adverse effects of aztreonam are local reactions at the site of injection. Interestingly, aztreonam rarely causes allergic reactions in patients with a history of type I hypersensitivity to other (3-lactam antibiotics. 

Other agents which contain the p-lactam ring include aztreonam and the carbapenems. Aztreonam is an unusual p-lactam for two reasons its antibacterial activity is exclusively Gram-negative and it is reported to carry very low risk of anaphylaxis in individuals who are penicillin-hypersensitive. 

Aztreonam Prevents bacterial cell wall synthesis by binding to and inhibiting cell wall transpeptidases Rapid bactericidal activity against susceptible bacteria Infections caused by aerobic, gram-negative bacteria in patients with immediate hypersensitivity to penicillins IV administration renal clearance half-life 1.5 h dosed every 8 h Toxicity No cross-allergenicity with penicillins... 

Koch C, Hjelt K, Pedersen SS, Jensen ET, Jensen T, Lanng S, Valerius NH, Pedersen M, Hoiby N. Retrospective clinical study of hypersensitivity reactions to aztreonam and six other beta-lactam antibiotics in cystic fibrosis patients receiving multiple treatment courses. Rev Infect Dis 1991 13(Suppl 7) S608-11. 

Imipenem, which is related to meropenem, has also been reported to cause toxic epidermal necrolysis (34). The authors stated that to the best of their knowledge, this was the first report of a possible cross-reaction between two classes of antibiotics in causing toxic epidermal necrolysis. The time between first administration and the occurrence of epidermal necrolysis is considerably shorter in recurrence or provocation testing (35,36). They also claimed that it is likely that the beta-lactam ring is responsible for this hypersensitivity reaction, citing the evidence that the patient had been given amoxicillin 15 days before the cephalosporin, and that could have served as the sensitizing event. They did not discuss whether aztreonam, a monobactam, also could have caused a cross-reaction however, it has been involved in two cases of fatal toxic epidermal necrolysis (37). 

Immediate hypersensitivity related to imipenem has been reported in a patient allergic to penicillin and aztreonam (41). 

Negligible cross-reactivity has been reported in both animal and human studies involving hapten inhibition, skin tests, and treatment of penicillin-allergic patients with therapeutic doses of aztreonam (12,14-19). Aztreonam therefore seems to be a safe alternative for patients with penicillin allergy. However, the numbers of safely treated patients reported are still small, and immediate type hypersensitivity to aztreonam has been reported in patients with penicillin allergy (20-23). 

Jensen T, Koch C, Pedersen SS, Hoiby N. Aztreonam for cystic fibrosis patients who are hypersensitive to other beta-lactams. Lancet 1987 l(8545) 1319-20. 

Soto Alvarez J, Sacristan del Castillo JA, Sampedro Garcia I, Alsar Ortiz MJ. Immediate hypersensitivity to aztreonam. Lancet 1990 335(8697) 1094. 

Patients with delayed reactions to penicillin (skin rash) generally can receive cephalosporins. Patients with type I hypersensitivity reactions to penicillins (anaphylaxis) should not receive cephalosporins or carbapenems (alternatives include aztreonam, quinolones, sulfa drugs, or vancomycin based on type of coverage indicated). 

Each of the dmgs listed has activity against some gram-negative bacilli. All penicillins should be avoided in patients with a history of allergic reactions to any individual penicillin drug. Cephalosporins should also be avoided in patients who have had anaphylaxis or other severe hypersensitivity reactions following use of a penicillin. There is no cross-reactivity between the penicillins and aztreonam. The answer is (B). 

The question of tolerability of penicillins, monobactams, and carbapenems in patients with IgE hypersensitivity to cephalosporins was recently assessed in 98 subjects by serum IgE antibody assays, challenge tests, and skin testing with penicillin reagents, aztreonam, imipenem-cilastatin, and meropenem. Approximately 25 % of cephalosporin-allergic subjects were positive to penicillins, while 3.1,2, and 1 % showed positive results to aztreonam, imipenem, and meropenem, respectively. A reaction to a cephalosporin with a similar or identical side chain to penicillin was a sigifificant predictor of cross-reactivity. For skin testing, the following concentrations were used ampicillin and amoxicillin 1 and 20 mg/ml cephalosporins 2 mg/ml aztreonam 2 mg/ml imipenem-cilastatin 0.5 mg/ml and meropenem 1 mg/ml. 

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