This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pharmacology
Which drug is effective against both pseudomonas and proteus: September 2005 
Select and explain. 
A. Cloxacillin, B. Amoxycillin, C. Carbenicillin, D. Ampicillin
C: Carbenicillin
Answer: C: Carbenicillin 
Explanation: Ans. C: Carbenicillin Carbenicillin is a bactericidal and bacteriolytic antibiotic belonging to the carboxypenicillin subgroup of the penicillins. It has Gram-negative coverage which includes Pseudomonas aeruginosa but limited Gram-positive coverage. The catboxypenicillins are susceptible to degradation by beta-lactamase enzymes, although they are more resistant than ampicillin to degradation. Carbenicillin is also more stable at lower pH than ampicillin. The antibiotic is very soluble in water and is acid-labile. Aqueous solutions are sho-lived. It is a semi-synthetic analogue of the naturally occurring benzyl-penicillin.