Rhodococcus equi Medication

Updated: Apr 13, 2015
  • Author: Indira Kedlaya, MD; Chief Editor: Burke A Cunha, MD  more...
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Medication

Medication Summary

In vitro susceptibilities

R equi is usually susceptible to the following medications:

  • Erythromycin
  • Azithromycin
  • Clarithromycin
  • Ciprofloxacin
  • Vancomycin
  • Aminoglycosides
  • Rifampin
  • Imipenem
  • Meropenem
  • Linezolid

R equi is usually resistant to penicillin G, ampicillin, carbenicillin, and cefazolin. Sensitivities to clindamycin, ceftriaxone, trimethoprim, sulfamethoxazole, tetracycline, and chloramphenicol vary. Although the organism sometimes shows sensitivity to beta-lactams in vitro, several reports have described acquired resistance to them during treatment. Clarithromycin has been shown to be at least as effective as erythromycin. However, azithromycin seems less active.

Medical treatment

A study based on animals experiments demonstrated that the effective single agents against R equi include vancomycin, imipenem, and rifampin. In the same study, combinations of antibiotics were not more effective than vancomycin alone. However, combinations of antibiotics may limit the emergence of in vivo antibiotic-resistant mutants. Munoz et al (2008) reported successful linezolid monotherapy for pulmonary R equi infection in a heart transplant recipient. [15] However, the initial therapy in this patient consisted of a combination of parenteral antibiotics.

Many authors recommend the use of combination antibiotics. Some also recommend using at least one antibiotic with intracellular penetration (eg, erythromycin, rifampin). In vitro synergy studies demonstrated 4 combinations of antibiotics to be effective against R equi infection (ie, rifampin-erythromycin, rifampin-minocycline, erythromycin-minocycline, imipenem-amikacin). In the same study, the combination of macrolides and aminoglycosides was found to be antagonistic. However, it has been used with success clinically. Recommendations for combination therapy in HIV-infected patients include imipenem-vancomycin, imipenem-teicoplanin, and combinations based on macrolides and rifampin. [8]

A few cases of brain abscesses and nosocomial meningitis have been reported in immunocompetent patients. In a case report by Scotton et al, a patient with nosocomial meningitis was initially treated with vancomycin and rifampin. [16] However, because of continued fever, monotherapy with levofloxacin was instituted with success. Clinical success with vancomycin monotherapy followed by oral sulfamethoxazole-trimethoprim has been documented in an immunocompetent patient with brain abscess, in addition to neurosurgical treatment.

However, monotherapy should generally not be used to treat systemic R equi infections. In a case report published by Gabriels et al in 2006, initial monotherapy with levofloxacin was unsuccessful. [17] This was followed by recurrent infections and death in an immunocompetent patient. The organism was initially sensitive to levofloxacin but later acquired resistance to the antibiotic.

Giguere et al retrospectively compared combination therapy with azithromycin-rifampin, clarithromycin-rifampin, and erythromycin-rifampin in foals with R equi pneumonia. [18] The combination of clarithromycin-rifampin was superior to the other 2 groups of therapy.

In general, pulmonary infections should be treated for a minimum of 2 months. Treatment should initially consist of parenteral antibiotics followed by oral combination therapy. One author has recommended initial therapy with a vancomycin-based regimen followed by oral combination therapy with rifampin plus erythromycin or rifampin plus minocycline. The average duration of antibiotic therapy in a review of R equi infections in renal transplant recipients was 6.5 months. [12]

In immunocompetent patients, a shorter duration of therapy may be considered because R equi infection has been treated successfully with shorter courses. Selective local R equi infections without evidence of systemic involvement can be treated with shorter courses of antibiotics, with or without local surgical resection. Topical antibiotics have also been used in R equi endophthalmitis, in combination with systemic antibiotics and surgical therapy.

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Antibiotics

Class Summary

Therapy must be comprehensive and cover all likely pathogens in the context of this clinical setting.

Vancomycin (Vancocin)

Potent antibiotic directed against gram-positive organisms. Useful in the treatment of septicemia and skin-structure infections. Indicated for patients who cannot receive, or whose conditions have failed to respond to, penicillins and cephalosporins or who have infections with resistant staphylococci. To avoid toxicity, current recommendation is to assay vancomycin trough levels after third dose drawn 0.5 h prior to next dosing. Use CrCl to adjust dose in patients diagnosed with renal impairment.

Rifampin (Rimactane, Rifadin)

Inhibits DNA-dependent bacterial, but not mammalian, RNA polymerase.

Erythromycin (EES, E-Mycin, Eryc)

Inhibits bacterial growth, possibly by blocking dissociation of peptidyl tRNA from ribosomes, causing RNA-dependent protein synthesis to arrest.

Ciprofloxacin (Cipro)

Fluoroquinolone with activity against streptococci, MRSA, Staphylococcus epidermidis, and most gram-negative organisms, including Pseudomonas, but no activity against anaerobes. Inhibits bacterial DNA synthesis and, consequently, growth.

Gentamicin (Garamycin)

Aminoglycoside antibiotic for gram-negative coverage. Follow each regimen by at least a trough level drawn on the third or fourth dose (0.5 h before dosing). May draw a peak level 0.5 h after 30-min infusion.

Imipenem and cilastatin (Primaxin)

For treatment of multiple-organism infections in which other agents do not have wide-spectrum coverage or are contraindicated owing to potential for toxicity.

Meropenem (Merrem IV)

For treatment of multiple-organism infections in which other agents do not have wide-spectrum coverage or are contraindicated owing to potential for toxicity. Has slightly increased activity against gram-negative organisms and slightly decreased activity against staphylococci and streptococci compared to imipenem.

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