Step 1: Bronchiolitis is the inflammation of the smallest airways in infants and is driven by viruses, RSV being the leading culprit. The question asks which listed option does NOT belong to its treatment.
Step 2: Supportive care is the backbone of therapy. Humidified oxygen relieves hypoxia and bronchodilator nebulizations are commonly trialled to open the airways, so both of those are genuine treatment measures.
Step 3: Antibiotics, including macrolides, target bacteria and therefore offer nothing against a viral infection. They are reserved only for proven bacterial superinfection. That leaves macrolides as the odd one out.
\[\boxed{\text{Macrolides}}\]