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NAVLE® Question of the day

MO TU WED TH FR

May 8, 2024

NAVLE

A four-month-old filly is presented with a four-day history of lethargy, heavy breathing, cough and decreased appetite.

Value	Normal
104.9°F (40.5°C)	99.0–100.6°F (37.2–38.1°C)
HR=72 bpm	28-40 bpm
R=44 brpm	10-14 brpm

On lung auscultation asymmetrically-distributed crackles and wheezes are audible. Some areas have no breath sounds and a dull resonance on thoracic percussion. A lateral chest radiograph shows consolidated nodular lung lesions and mediastinal lymphadenopathy.

Pneumonia due to Rhodococcus equi infection is confirmed based on culture and polymerase chain reaction results on a transtracheal wash.

Which one of following choices is the most appropriate treatment?

A - Tilmicosin

B - Chloramphenicol and aminophylline

C - Procaine penicillin G and gentamicin

D - Vancomycin and atropine (if bronchospasm is observed)

E - Clarithromycin and rifampin

Sorry. You chose "C - Procaine penicillin G and gentamicin" but the correct answer is "E - Clarithromycin and rifampin"

Start this filly on clarithromycin and rifampin.

In this case, a chest radiograph with consolidated nodular lung lesions and mediastinal lymphadenopathy is highly suggestive of Rhodococcus equi in a foal under five months of age.

Polyarthritis, polysynovitis, and diarrhea can also be seen in affected foals.

Combination treatment of rifampin combined with either erythromycin, clarithromycin, or azithromycin is appropriate to treat R. equi pneumonia.
However, in one retrospective study, the combination of clarithromycin and rifampin was shown to be the most effective of the three.
Tilmicosin, while a macrolide, is not very active against R. equi and swelling can occur at injection sites in foals; it is not recommended for treatment of R. equi pneumonia.

Click here to see an ultrasound video from Merck of a three-month-old foal with rhodococcal pneumonia.