Under what circumstances might antibodies not be useful in treating a disease caused by a pathogen?

When the disease is caused by viral infection, antibiotic will not be effective in treating the disease. Pathogens may also possess antibiotic resistance.

Antibiotics fail to prevent viral multiplication as such pathogens use our cell machinery to multiply. Viral particles do not have their own system that could be targeted by antibiotic medicines.

Several bacterial populations develop resistance to different antibiotics. It is important to find the susceptibility of infecting bacteria to decide which particular antibiotic should be used for treatment.