This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Chemotherapy: General Principles, Subject name: Pharmacology
Which of the following beta-lactam antibiotics can be safely used in a patient with a history of allergy to penicillins? 
Select and explain. 
A. Aztreonam, B. Cefepime, C. Loracarbef, D. Ceftriaxone
A: Aztreonam
Answer: A: Aztreonam 
Explanation: Ans. (A) Aztreonam(Ref: KDT 8/e p781)Aztreonam is the only beta lactam antibiotic that can be used in patients having severe allergy to penicillins or cephalosporins (as it is not cross allergenic).