The short answer to your question is that a small quantity of alcohol (beer) taken about the same time as a dose of azithromycin should not cause a problem or make the treatment less effective.
Azithromycin (common trade name, Zithromax® or Z-Pak) may be taken either with or without food, but should not be taken within 2 hours of using antacids that contain aluminum or magnesium.
Your concern and question are good because alcoholic beverages do cause interactions with some medications, and you should know this information and follow the instructions of your doctor or pharmacist carefully.
–James Allen, MD, MPH