Which of the following therapeutic agents is NOT classified as a broad-spectrum antibiotic?

Penicillin (specifically classical Penicillin G) is a narrow-spectrum antibiotic because it acts primarily against a limited group of Gram-positive bacteria. On the other hand, Tetracycline and Chloromycetin (Chloramphenicol) are broad-spectrum antibiotics effective against a wide range of Gram-positive and Gram-negative bacteria.