It is antiviral:

Explanation

Penicillin, tetracycline, and streptomycin are antibiotics that specifically target structures and processes unique to bacteria, which is why they are not effective against viruses. For example, penicillin interferes with bacterial cell wall synthesis, tetracycline inhibits bacterial protein synthesis by binding to the 30S ribosomal subunit, and streptomycin also acts on bacterial ribosomes, causing errors in protein production. Since viruses lack cell walls, ribosomes, and the metabolic machinery necessary for independent life, these antibiotics have no targets to act upon within viral particles or infected host cells. In contrast, interferons are naturally occurring proteins produced by host cells in response to viral infection, and they work by enhancing the body's antiviral defenses. They do not directly kill viruses but instead stimulate nearby uninfected cells to produce antiviral proteins, inhibit viral replication, and boost the immune response by activating natural killer cells and macrophages. This fundamental difference explains why antibiotics like penicillin, tetracycline, and streptomycin are useless against viruses, while interferons play a direct role in controlling viral infections.