Which category of drugs is NOT typically used to treat gram-negative organisms?

Penicillins are traditionally not as effective against many gram-negative organisms compared to other classes of antibiotics. This is largely due to the structure of the gram-negative bacterial cell wall, which is more complex and impermeable than that of gram-positive bacteria. While some modified penicillins, such as aminopenicillins, have been developed to extend activity against certain gram-negative bacilli, the general category of penicillins is less reliable for a broad spectrum of gram-negative pathogens.

In contrast, cephalosporins are often specifically designed to target gram-negative bacteria, with later generations showing increased effectiveness. Macrolides primarily target gram-positive organisms and atypical bacteria but tend to have limited activity against gram-negative species. Polymyxins are particularly utilized for gram-negative infections and are effective against multi-drug-resistant strains. This specificity highlights why penicillins are not typically the first choice when treating infections caused by gram-negative organisms.