Which of these penicillins is NOT classified as broad spectrum?

Nafcillin is considered a narrow-spectrum penicillin primarily effective against certain bacteria, particularly those in the Staphylococcus family. It is specially designed to combat penicillin-resistant strains of Staphylococcus aureus. Unlike broad-spectrum penicillins, which have a wider range of activity against both Gram-positive and Gram-negative bacteria, Nafcillin's effectiveness is more limited, focusing on specific Gram-positive bacteria.

Amoxicillin and Ampicillin belong to the broad-spectrum category as they are effective against a wider variety of organisms, including some Gram-negative bacteria. Dicloxacillin is similar to Nafcillin in that it targets specific Gram-positive organisms but is often categorized with other penicillins that are resistant to penicillinase. Thus, the distinguishing factor that classifies Nafcillin as not broad spectrum is its narrow activity profile compared to other penicillins that cover a larger array of bacterial pathogens.