November 3, 2012 | Veterinary Record Papers Papers Plasma disposition of enrofloxacin following intravenous and intramuscular administration in donkeys S. Sekkin, C. Gokbulut, C. Kum, U. Karademir This study was designed to investigate the plasma disposition and systemic availability of enrofloxacin (ENR) following intramuscular and intravenous administrations. Six donkeys (Equus asinus) were used in this study. The animals were allocated into two groups (intramuscular and intravenous groups). After a 2-week washout period, the experiment was repeated with the groups reversed according to a two-phase crossover design. In phase I, group I received intravenously the commercially available injectable solution of ENR at the dose of 5 mg/kg and group II received intramuscularly the same ENR formulation at the same dose rate. Blood samples were collected 1 hour prior to drug administration and various times between 5 minutes and 48 hours post-treatments. The samples were analysed by high performance liquid chromatography with fluorescence detector. The half- life and mean residence time of ENR (12.08 hours and 17.85 hours) after intramuscular route were significantly longer compared with intravenous administration (9.54 hours and 7.46 hours, respectively) and these were associated with a flip-flop phenomenon. A marked proportion of ENR (20–21 per cent) was metabolised to ciprofloxacin (CPR) following both administration routes and the half-life of CPR paralleled that of the parent drug after intramuscular administration. Mean absorption time was relatively long (10.39 hours), and the bioavailability of ENR was 76.56 per cent after intramuscular route in the donkeys. The plasma concentration is lower after intramuscular administration at a dose rate of 5 mg/kg, and may need a higher dose to provide sufficient plasma concentration in donkeys compared with horses. Introduction Enrofloxacin (ENR) is a synthetic antibacterial agent of the fluoro- quinolones, and it is extensively used for treatment of infections in humans and animals (Altreuher 1987). ENR has a broad spectrum of activity against a variety of pathogens, including Gram-positive and Gram-negative bacteria, mycoplasmas and intracellular pathogens, such as Brucella and Chlamdia species (Neu 1987, Wolfson and Hooper 1991, McKellar and others 1999). Some fluoroquinolones, such as danofloxacin, moxifloxacin, mar- bofloxacin and ENR, are being used widely in horses (Bertone and others 2000, Carretero and others 2002, Gardner and others 2004). In addition, pharmacokinetic disposition of ENR in horses has been well studied (Langston and others 1996, Kaartinen and others 1997, Bermingham and others 2000, Papich and others 2002, Epstein and others 2004, Peyrou and others 2006, Steinman and others 2006). On the other hand, there is a paucity of data available on the pharmacoki- netics of drugs used in donkeys, including antibiotics, since donkeys were often a neglected species in domestic animals. Nevertheless, there is an increasing interest on donkey farming due to the develop- ment of their use in leisure activities, onotherapy which is a type of pet or animal-assisted therapy popular in Italy using donkeys, and in particular the rediscovery of donkey milk as food source for children affected by cow milk allergy (Carroccio and others 2000). Different classes of drugs used in horses and ruminants are com- monly extrapolated to donkeys without optimisation of dosing regi- mens and determination of pharmacokinetic and pharmacodynamic properties. Because of the lack of registered drugs for donkeys, anti- microbials licensed for horses or ruminants are used for treatment of bacterial infections in this species with the same dose rates. It has been reported that donkeys have a greater capacity to metabolise certain drugs compared with horses; thus, higher dosage or shorter intervals are required for maintaining effective concentrations (Welfare and oth- ers 1996, Matthews and others 1997, Coakley and others 1999, Peck and others 2002, Grosenbaugh and others 2011). Therefore, the aim of the present study was to determine the pharmacokinetic properties of ENR in donkeys following intravenous and intramuscular administra- tion at a single dose of 5 mg/kg bodyweight. Material and methods Experimental animals Six donkeys (Equus asinus) which ranged in age from two to five years, weighing 90–125 kg bodyweight, were used in this study. The animals were kept indoors and had clover, hay and water available Veterinary Record (2012) doi: 10.1136/vr.100653 S. Sekkin, DVM, PhD C. Gokbulut, DVM, PhD C. Kum, DVM, PhD U. Karademir, DVM, PhD Department of Pharmacology and Toxicology, Faculty of Veterinary Medicine, University of Adnan Menderes, Bati Kampusu, Aydin, Turkey E-mail for correspondence: cengizgokbulut@yahoo.com Provenance: not commissioned; externally peer reviewed Accepted September 7, 2012 group.bmj.com on December 7, 2012 - Published by veterinaryrecord.bmj.com Downloaded from