There are a lot of variables here, so it is not easy to give a straight answer.
Depends on the type of pneumonia, the severity (if the patient is being treated in hospital or as an outpatient), age of the patient etc.
Two commonly used drugs are Azithromycin and
Clarithromycin
You will find information on these drugs on this website
http://azithromycin.drugs.com http://clarithromycin.drugs.com