10.2.2—Why antibiotics don't affect viruses

Antibiotics work against bacterial structures or processes, but a virus is not a bacterial cell. A virus therefore does not provide the bacterial targets that an antibiotic such as penicillin is designed to affect.

• Bacterial target exists: an antibiotic can interfere with a bacterial cell-wall process, membrane protein, enzyme, DNA process or protein-synthesis process. Penicillin, for example, acts on strengthening a growing bacterial cell wall.
• Viral target is absent: viruses have no bacterial-style cell wall and do not carry out growth and reproduction as independent bacterial cells. During replication they use the host cell’s transcription and translation machinery.
• Treatment consequence: blocking a bacterial target cannot stop the virus from using host-cell machinery, so an antibiotic does not treat the viral infection.

This is a target-matching rule, not a diagnosis from symptoms alone. Cholera and TB are bacterial diseases for which antibiotics may be relevant, whereas HIV is viral and is not treated by antibiotics.

“Antibiotics do not affect viruses” means that antibacterial targets are absent from viruses; it does not mean that no medicine can ever act against a virus. Resistance and other reasons for treatment failure are separate topics, not part of this target distinction.