Which complication is not preventable by antibiotics in cases of strep throat?

Glomerulonephritis is a complication that can occur following a streptococcal throat infection, but it is not preventable by antibiotics. This condition arises as a result of an immune response to the streptococcal bacteria, where antibodies formed against the bacteria can cross-react with the glomeruli in the kidneys and lead to inflammation.

While antibiotics are effective in treating streptococcal infections and can prevent certain complications such as rheumatic fever and peritonsillar abscess by eradicating the bacteria from the throat, they do not prevent glomerulonephritis. This condition is typically a result of post-streptococcal glomerulonephritis, which occurs after the infection has already taken place and is influenced by the body's immune response rather than the ongoing presence of the bacteria.

The other options listed—rheumatic fever, peritonsillar abscess, and cellulitis—are complications that can be effectively reduced or prevented through appropriate antibiotic treatment when strep throat is identified and treated in a timely manner.