Use of dapsone in the treatment of Pneumocystis carinii pneumonia in a foal.

This study discusses the diagnosis and treatment of a 6-month-old male Quarter Horse diagnosed with Pneumocystis carinii pneumonia. The horse was successfully treated with dapsone, an antibiotic traditionally used in humans, after presenting with secondary complications including antimicrobial-associated colitis and bilateral fibrinous hypopyon following initial treatment with trimethoprim-sulfamethoxazole.

Study Overview

The research paper details the diagnosis and treatment process of a Quarter Horse foal suffering from chronic respiratory tract disease. After conducting diagnostic investigations, the horse was found to have a pulmonary inflammation along with Pneumocystis carinii, an opportunistic fungus, within its macrophages.

Initial Diagnosis and Treatment

• The researchers performed lymphocyte subpopulation phenotyping and immunoglobulin concentration analysis. The results pointed towards immune suppression in the horse.
• Initial treatment involved administration of the antibiotic Trimethoprim-sulfamethoxazole, often used to treat respiratory tract infections.

Complications and Adjusted Treatment

• Eight days post-discharge, the foal was reexamined due to severe diarrhea and endotoxemia (presence of toxins in the blood), triggered by an antimicrobial-associated colitis.
• A fecal bacterial culture test identified the presence of Salmonella spp, resistant to the initially administered Trimethoprim-sulfamethoxazole antibiotic.
• The foal also developed bilateral fibrinous hypopyon (inflammation in the eye), which was treated with topical medication and intracameral injections of human recombinant tissue plasminogen activator.

Introducing Dapsone

• Dapsone, an antibiotic typically used in humans, was provided as a treatment for Pneumocystis carinii pneumonia after adjusting for equine dosage.
• The foal successfully recovered from both pneumonia and diarrhea after 56 days of dapsone treatment.

Implications of the Study

The successful use of dapsone in treating the Quarter Horse foal indicates its potential use in horses as either an adjunct to traditional treatments for Pneumocystis carinii pneumonia or as a sole medication for horses unable to tolerate other treatments.