Horses antimicrobial treatment

Antimicrobial agents are used frequently in horses with gastrointestinal disorders but in most cases their use is empirical. For some infectious disorders of the alimentary tract, there are specific antimicrobial treatments, including ... 

Erythromycin estolate in conjunction with rifampin (both drugs administered orally) can be recommended for the treatment of Rhodococcus equi pneumonia in foals. Early diagnosis of the infection and prompt initiation of therapy considerably increase the effectiveness of treatment. Apart from this specific indication, macrolide antibiotics (including erythromycin) and lincosamides (lincomycin and clindamycin) are contra-indicated in horses. Antimicrobial agents in these classes can cause severe disturbance of the balance between commensal bacterial flora in the colon of the horse. 

In companion animals, the bacterial infections most frequently requiring treatment involve the skin, wounds, ears, respiratory tract, and urinary tract. Prevalence of resistant bacteria is difficult to assess in pets. Since empirical treatment is common, there is limited information on trends in resistance, and almost no data are available on the magnitude of antimicrobial use in these species. Increasing resistance among E. coli and Staphylococcus isolates from pets has been reported from studies in a number of countries. Methacillin-resistant Staphylococcus aureus (MRSA) have been isolated from dogs and horses, although animal outbreaks have generally been traced to infected humans. ... 

The tetracyclines are amphoteric antimicrobial agents that can form salts with bases or acids (see Chs 1 and 2). Oxytetracycline is a bitter, yellow, odorless crystalline powder. The base is slightly water soluble and the hydrochloride is readily water soluble and is typically administered to horses by slow i.v. injection. It is effective at 5.5 mg/kg once daily for 2 days or more in the treatment of B. equi but is unlikely to completely clear this infection. It is, therefore, used for premunition. Rapid i.v. injection may cause a precipitous drop in blood pressure and collapse owing to the effects of calcium chelation on the myocardium. Intramuscular injection causes objectionable local reactions in horses and should be avoided. Oral administration may be more... 

The treatment of UTIs in horses consists of proper antimicrobial therapy and, if possible, the correction of the predisposing anatomical or functional problems with urine flow (e.g. outflow... 

It warrants mention that resistance to a particular antimicrobial agent in vitro may not preclude successful treatment with the drug as long as high concentrations are achieved in urine. Similarly, demonstrable susceptibility in vitro does not always guarantee a successful response to treatment. For example. Enterococcus spp. is often found to be susceptible to the potentiated sulfonamide combinations in vitro however, this pathogen is inherently resistant to these combinations in vivo (Jose-Cunilleras Hinchcliff 1999, Schott 1998). Antimicrobial therapy should be continued for at least 1 week for the treatment of lower UTIs and for 2-6 weeks for upper UTls in horses. Ideally, a voided, midstream urine sample should be submitted for bacterial culture 2-4 days after the initiation of therapy and again 1-2 weeks after treatment has been discontinued. 

The cephalosporins and tetracyclines are commonly used for treatment of UTIs in other species. However, in horses, the cephalosporins are rarely more advantageous than the penicillins or potentiated sulfonamides. However, ceftiofur has broad-spectrum antimicrobial activity and may be indicated when urinary pathogens are resistant to... 

The treatment of endometritis should include antimicrobial therapy based on culture and susceptibility testing (see Ch. 2). The treatments used commonly for bacterial and fungal uterine infections in horses are included in Tables 11.1 and 11.2. Fungal or yeast infections often result from the extensive use of antimicrobial agents in the uterus. These infections are difficult to treat and may cause permanent damage to the endometrium. An intrinsic problem with uterine yeast or fungal infections is the prolonged and potentially expensive therapy required. 

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