Susceptibility of bacteria from feline and canine urinary tract infections to doxycycline and tetracycline concentrations attained in urine four hours after oral dosage

Abstract

Objectives To measure urinary concentrations of doxycycline in cats and dogs and tetracycline in dogs 4 h after conventional oral dosing and determine whether these antibiotics were present in sufficient concentrations to be effective against common feline and canine urinary tract pathogens as assessed in vitro by Epsilometer and disc diffusion antimicrobial susceptibility methods. Design A prospective study involving oral administration to clinically normal cats and dogs of doxycycline or tetracycline (dogs only) and culture of bacteria from dogs and cats with urinary tract infections to determine their susceptibility to both doxycycline and tetracycline in vitro. Procedure In the first study, nine cats and eight dogs were administered doxycycline monohydrate (5 mg/kg every 12 h) and a further eight dogs were administered tetracycline hydrochloride (20 mg/kg every 8 h) for 72 h. Blood was collected at 2 and 4 h, and urine at 4 h, after the last dose. The concentration of each agent in serum and urine was determined by modified agar diffusion. In the second study, 45 urine samples from cats and dogs with urinary tract infections were cultured. Every bacterial isolate was tested in vitro using both Epsilometer (doxycycline and tetracycline) and disc diffusion (doxycycline, tetracycline or amoxycillin‐clavulanate) tests. Results Serum doxycycline concentrations in sera of cats and dogs at 2 h were 4.2±1.0 mg/mL and 3.4±1.1 mg/mL, respectively. The corresponding concentrations at 4 h were 3.5±0.7 mg/mL and 2.8±0.6 mg/mL. Urinary doxycycline concentrations at 4 h (53.8±24.4 mg/mL for cats and 52.4±24.1 mg/mL for dogs) were substantially higher than corresponding serum values. Serum tetracycline concentrations in dogs at 2 and 4 h, and in urine at 4 h, were 6.8±2.8, 5.4±0.8, 144.8±39.4 mg/mL, respectively. Most of the urinary tract pathogens (35/45) were susceptible to urinary concentrations of doxycycline and 38/45 were susceptible to tetracycline. In contrast 41/45 of all isolates were susceptible to amoxycillin‐clavulanate. Conclusion This is the first report of urinary concentrations of doxycycline after conventional oral administration. Concentrations attained in the urine of normal cats and dogs were sufficient to inhibit the growth of a significant number of urinary tract pathogens and thus doxycycline may be a useful antimicrobial agent for some urinary tract infections.

In vitro susceptibilities of feline and canine Escherichia coli and Pseudomonas spp. isolates to ticarcillin and ticarcillin–clavulanic acid

“…The comparative results of that 1994 study may infer that a greater number of resistant E. coli isolates are collected from North American than Australian dogs. Similar observations have been noted with other antibacterials, such as fluoroquinolones and tetracyclines, against Australian canine and feline E. coli isolates . Likewise, a low number of ticarcillin‐susceptible E. coli isolates (45%) from canine urine samples was reported from Portugal; however, our study had a susceptibility of 75%.…”

Bacterial Isolates from Urinary Tract Infection in Dogs in Grenada, and Their Antibiotic Susceptibility

“…Among the 6 antibiotics tested, resistance was most frequent to tetracycline. However, a recent study [11], showed that concentrations of doxycycline attained in the urine of dogs were sufficient to inhibit the growth of a significant number (35/45) of urinary tract pathogens. In any case, the present study showed that enrofloxacin had the least resistance; more than 80% of all isolates being susceptible.…”

Pharmacodynamics of Doxycycline and Tetracycline against Staphylococcus pseudintermedius: Proposal of Canine-Specific Breakpoints for Doxycycline

“…Prior to this study, a few studies have been published to describe PK properties of doxycycline in dogs (10)(11)(12)(13)(14)(15)(16)(17). One additional study was identified (30), but analysis of the plasma concentrations from that study produced values far out of the range of those listed in Table 1; therefore, those data were not incorporated into this analysis.…”

“…The pharmacokinetics of doxycycline in dogs have been assessed in previously published studies on the oral administration of doxycycline (10,11), the findings of a conference presentation (A. Dominguez, B. Kukanich, and K. Kukanich, presented at the American Academy of Veterinary Pharmacology and Therapeutics 18th Biennial Symposium, Potomac, MD, 20 to 23 May 2013), and one unpublished study performed by one of the veterinary drug sponsors (S. T. B. Rogar, unpublished data). Other studies of nonoral administration in dogs have been published for comparison with studies of oral administration and determination of protein binding (12)(13)(14)(15)(16)(17). The oral administration studies used for this analysis used a validated assay and uniform methods.…”