Glycopeptide antibiotics are a class of antibiotic drugs. The class is composed of glycosylated cyclic or polycyclic nonribosomal peptides. They are used if infection by methicillin-resistant Staphylococcus aureus is suspected. Due to their toxicity, use of glycopeptide antibiotics is restricted to patients who are critically ill, who have a demonstrated hypersensitivity to the β-lactams, or who are infected with β-lactam-resistant species. These antibiotics are effective principally against Gram-positive cocci. They exhibit a narrow spectrum of action, and are bacteriocidal only against the enterococci. Some tissues are not penetrated very well by glycopeptides, and they do not penetrate into the cerebrospinal fluid.