Which condition is erythromycin primarily used to treat?

Erythromycin is primarily used to treat chest infections because it is a macrolide antibiotic that is effective against a variety of bacteria responsible for respiratory tract infections. These include conditions such as pneumonia, bronchitis, and other chest infections caused by susceptible organisms. Its mechanism of action involves inhibiting bacterial protein synthesis, which ultimately leads to the cessation of bacterial growth and helps in managing infections in the respiratory system effectively. This makes it particularly useful in treating patients with respiratory infections when penicillin is not suitable or when the bacteria are resistant.

In contrast, the other conditions listed require different treatments. Diabetes is typically managed with insulin or oral hypoglycemic agents, bacterial meningitis is treated with more potent antibiotics specific to the causative organism, and cardiac arrhythmias require antiarrhythmic medication or intervention rather than antibiotics like erythromycin.