Thank you for your question and for visiting the family practice forum.
I suspect your son is having some upper airway inflammation or irritation which causes the persistent cough. Clearly, following pneumonia, the airways may be indeed more sensitive for a period of time. In this case (and in yours) it appears as though the cough is persisting much longer than expected.
I would first get Pulmonary Function Testing (PFTs). This will help determine if, in fact, the problem is asthma. If it is asthma, it needs to be treated. Ventolin is an inhaler to be used to "bronchodilate" or open up the airways during an asthma attack. Medications such as Azmacort (steroid inhaler) are used to "prevent" symptoms of asthma (in this case.. prevent the cough). Other medications such as "singulair" and "accolate" are also used to help "prevent" asthma symtpoms. If the PFTs show that there is asthma, this is where I would start (i.e. BEFORE using medications such as Ventolin).
Now, Asthma is a likely possibility here, but what else could it be? Well, common causes for chronic cough in children include,
1. Asthma
2. Gastroesophageal reflux disease (notoriously underdiagnosed by family physicians and pediatricians)
3. Chronic Sinusitis
4. Allergic rhinitis - This one is one that is also "heredetary". If both you and your son experienced persistent cough and upper airway problems following pneumonia, you both may have an "allergy" to something. Common household allergens include dust mites, dog and cat dander, and molds.
Other less common causes include:
1. esophageal strictures
2. Tracheal (windpipe) narrowing (PFTs would help show this)
3. Enlarged tonsils
4. Inner ear problems.
It is also important to mention here that if there are smokers in the house, they need to STOP! Smoking is an all too common cause of upper respiratory symptoms and recurrent upper respiratory infections in children (forgive me if you are a non-smoker .. I just had to mention this!)
I wish you and your son well and hope this has been helpful!
Dean M. Tomasello, M.D.