In the Literature
Papich MG. Ciprofloxacin pharmacokinetics in clinical canine patients. J Vet Intern Med. 2017;31(5):1508-1513.
From the Page …
Fluoroquinolone antibiotics are commonly used in veterinary medicine to treat susceptible bacterial infections. Finding an antibiotic for large-breed dogs that is both efficacious and affordable can be challenging. Although relatively inexpensive, ciprofloxacin has variable bioavailability in healthy dogs,1 but less is known in patients with active infections, which may alter drug pharmacokinetics.
Dogs (n = 34) with active infections treated with ciprofloxacin (mean dose, 23.5 mg/kg PO q24h) were prospectively evaluated in a population-based pharmacokinetics study. This population-based approach can identify covariates (eg, presence of azotemia, age) that can alter drug pharmacokinetics. Body weight was the only identified covariate to cause variability in ciprofloxacin pharmacokinetics, with larger body weights associated with lower plasma drug concentrations, which could lead to ineffective antimicrobial therapy.
This study also evaluated plasma drug concentrations and the likelihood of ciprofloxacin killing an organism based on its minimum inhibitory concentration (MIC). Ideally, a dose schedule should produce a probability of clinical efficacy greater than 90%. The Clinical Laboratory and Standards Institute (CLSI) has established MIC breakpoints to define a bacterial isolate to be susceptible (S), intermediate (I), or resistant (R) to a particular antibiotic. Because ciprofloxacin breakpoints are unavailable for veterinary species, human breakpoints are used. This study found that a dosage of 25 mg/kg PO q24h provides more than 90% probability of efficacy against isolates with an MIC ≤0.06 µg/mL but only 64% probability for those with an MIC 0.12 µg/mL. To achieve a 90% probability for the latter MIC, a dosage of 50 mg/kg PO q24h is needed; a dosage of 10 mg/kg PO q24h did not achieve high probability of efficacy for any MIC.
At MICs ≥1 µg/mL, even ciprofloxacin at 50 mg/kg has essentially 0% probability of clinical efficacy.
The human CLSI breakpoint for bacteria susceptible to ciprofloxacin is ≤1 µg/mL. Veterinarians should be aware of the MIC from a culture result, not just the interpretation of S/I/R. This study’s results can be used to help determine whether ciprofloxacin can be effective and what dosage can provide a high probability of clinical success. Because large-breed dogs have lower blood concentrations, higher ciprofloxacin doses may need to be considered to help increase the likelihood of bacterial eradication. At ciprofloxacin MICs ≥1 µg/mL, alternative drugs should be considered.
… To Your Patients
Key pearls to put into practice:
Larger canine body weights have been shown to be associated with decreased plasma ciprofloxacin concentrations.
Clinicians must evaluate actual MICs from culture and susceptibility results and not simply rely on the interpretation of CLSI breakpoints.
If culture and susceptibility results indicate an MIC ≥1 µg/mL, alternative drugs should be considered.
- Papich MG. Ciprofloxacin pharmacokinetics and oral absorption of generic ciprofloxacin tablets in dogs. Am J Vet Res. 2012;73(7):1085-1091.
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