There are three major classes of antibiotics that are effective in treating a Legionella infection. These include the fluoroquinolones such as levofloxacin (Levaquin), and moxifloxacin (Avelox), the macrolides such as erythromycin, azithromyocin (Zithromax), and clarithromycin (Biaxin), and the tetracyclines including doxycycline (Vibramycin). A new class of antibiotics (glycylcyclines) are also effective. The choice of antibiotic is often dependent on the patient's clinical state, tolerance to the medication, and a health care professional's degree of certainty as to the diagnosis. Zithromax and Levaquin are particularly effective because of decreased gastrointestinal irritation, higher potency, better penetration into tissue, and once-daily dosing.In severe cases of Legionnaires' disease that seem more resistant to a single antibiotic, a second drug called rifampin (Rifadin) may be added.Pontiac fever requires no specific treatment.