Treatment of Infections Caused by Rhodococcus equi. 
Pneumonia caused by Rhodococcus equi remains an important cause of disease and death in foals.  The combination of a macrolide (erythromycin, azithromycin, or clarithromycin) with rifampin remains the recommended therapy for foals with clinical signs of infection caused by R equi.  Most foals with small, subclinical ultrasonographic pulmonary lesions associated with R equi recover without therapy, and administration of antimicrobial agents to these subclinically affected foals does not hasten lesion resolution relative to administration of a placebo.  Resistance to macrolides and rifampin in isolates of R equi is increasing.