The lack of pharmaceutical agents that are approved for use in pet birds in the United States is an important concern for veterinarians caring for avian species. As a result, drug doses used in those species are frequently derived from clinical reports or must be extrapolated from doses recommended for use in other species. This method of determining doses leads to issues that can be detrimental to the health of the bird being treated. Interest in the clinical pharmacology of pet bird species has increased in recent years and proper dosing of drugs and treatment of these animals has been improved as a result.
Marbofloxacina is a synthetic fluoroquinolone antimicrobial. Like other fluoroquinolones, it acts by inhibiting bacterial DNA gyrase. Marbofloxacin is safe and efficacious in other species and has rapid bactericidal activity against many gram-negative, and some gram-positive, aerobic organisms at relatively low concentrations.1 Efficacy against Staphylococcus intermedius, Escherichia coli, Proteus mirabilis, Pseudomonas spp, and Mannheima haemolytica has been reported.2-7 Marbofloxacin has similar or higher antibacterial activity and a broader antibacterial spectrum than other fluoroquinolones.1
Marbofloxacin was developed exclusively for veterinary use and is approved for treatment of skin and soft tissue infections in dogs and cats and for urinary tract infections (ie, cystitis) in dogs. Marbofloxacin is rapidly and almost completely absorbed from the gastrointestinal tract after oral administration in fasted animals, with a reported bioavailability of 94%.2 A study8 in dogs revealed that approximately 80% of marbofloxacin circulates unbound in the plasma. The drug is only minimally (approx 10% to 15% of drug dose) metabolized by the liver. Forty percent of an oral dose of marbofloxacin is excreted unchanged in the urine, with the remainder excreted unchanged (via the bile) in the feces.2
Because management of bacterial infections with antimicrobials is one of the most challenging aspects of the practice of avian medicine, a study was designed to determine the pharmacokinetics of marbofloxacin in blue and gold macaws (Ara ararauna), a species that is commonly kept as a companion animal and as a display animal in zoologic collections. Data derived from this study may be helpful in designing treatment regimens for bacterial diseases of blue and gold macaws and may yield information with clinical implications for other psittacine species.
Materials and Methods
Birds—Ten blue and gold macaws (3 males, 7 females) weighing 0.90 to 1.12 kg (mean, 1.04 kg) were used. Birds were usually housed outdoors in 2 group cages at Busch Gardens Tampa Bay. Birds were from 10 to 20 years of age and were fed a diet consisting of approximately 50% commercially prepared pellets,b various vegetables, and small amounts of fruit. Birds were permitted to adapt to inside housing in individual wire cages (3 × 3 × 3 m) for 6 weeks prior to initiation of the study. Immediately before the study, birds underwent physical examination. Examination findings, values for PCV and total plasma protein concentration, and behavioral variables were determined to be within reference range. The study was approved by the Institutional Animal Care and Use Committees of Kansas State University and Busch Gardens Tampa Bay.
Experimental design—Birds were stratified by weight and randomly allocated into 2 groups consisting of 5 birds each. Birds were fasted for 2 hours before administration of marbofloxacin and were fed 1 hour after administration in a crossover design. Marbofloxacinc (dose, 2.5 mg/kg) was administered orally via crop gavage to 5 birds and IV via the left basilic vein to 5 birds. Blood samples (0.75 mL) were collected from the jugular, right basilic, or tarsometatarsal veins in heparinized syringes at 0, 0.5, 1, 3, 6, 12, 24, 48, 72, and 96 hours after drug administration. Plasma was separated via centrifugation (10 minutes at approx 2,000 × g) and stored at −70°C until shipped to Kansas State University on dry ice; samples remained stored at −70°C until analyzed. After a 4week washout period, the study was repeated with the first 5 birds receiving the dose IV and the second 5 birds receiving the dose orally.
Marbofloxacin analysis—Concentrations of marbofloxacin in plasma were determined by use of an HPLC system with a mass spectrometer for detection.d The mobile phase consisted of 20:80 acetonitrile:water (vol:vol) with 10 mM formic acid. The flow rate was 0.2 mL/min. The acetonitrile used was HPLC grade, water was deionized in house, and the formic acid was certified American Chemical Society grade. Under those conditions, the retention times for marbofloxacin and enrofloxacin (used as in internal standard) were 3.6 and 4.8 minutes, respectively. The mass spectrometere was set up as follows: electrospray with positive ionization was used as the ionization source, and source voltage was set at 4.5 kV; sheath gas flow rate was set at 65 arbitrary units and auxiliary gas was set at 10 units; heated capillary had a temperature of 135°C and a voltage of 28 V; tube lens offset was 45 V, intermultipole lens voltage was −16 V; octapole 1 offset was −3 V; octapole 2 offset was −5.5 V. The ions at 363.2 and 360.2 m/z (mass-to-charge ratio) were used for quantitation of marbofloxacin and enrofloxacin, respectively. Both marbofloxacin and enrofloxacin were confirmed by use of mass spectrometry.
Standard and quality control samples were prepared in bulk by adding marbofloxacin-naïve macaw plasma to aliquots of water containing at least 10 times the intended final concentration of marbofloxacin. The resulting solutions were used for quality control and had concentrations of 0.01, 0.1, and 1.0 μg/mL. Five quality control samples at each concentration were extracted and assayed on the day of validation; for each subsequent assay, 2 samples at each concentration were thawed and extracted. Standards were prepared in duplicate for each day on which samples were assayed. The standard curve was linear, weighted 1/x, and concentrations ranged from 0.001 to 5.0 μg/mL. The intra- and interday validation results were within 10% of intended value for precision and accuracy. Recovery was > 70% over the range of the assay.
A sample of 200 μL was pipetted into a test tube, and a 50-μL aliquot of water containing 4 μg of enrofloxacin/mL was added. The solution was mixed, and a 3-mL aliquot of acetonitrile was added. The sample was vortexed for 10 minutes and centrifuged for 10 minutes at 2,000 × g. After centrifuging, the supernatant was transferred to a clean test tube and dried under N2 in a 40°C water bath. The sample was reconstituted with 200 μL of mobile phase, and the mixture was vortexed for 1 minute before the liquid was transferred to a vial for injection onto the liquid chromatography–mass spectrometer system. Injection volume was 50 μL.9
Pharmacokinetic calculations—Values of pharmacokinetic variables were determined for each bird by use of noncompartmental analysis10,11 performed with commercially available software.f Values calculated for IV administration of marbofloxacin were plasma AUC; AUMC; MRT, where MRT = AUMC/AUC; Vd, where Vd = dose × AUMC/AUC2; plasma clearance, where clearance = dose/AUC; elimination rate constant (λz) calculated as the slope of the terminal phase of the plasma concentration curve that included a minimum of 3 time points; and t½, where t½ = 0.693/λz. For the orally administered dose of marbofloxacin, the following variables were determined: AUC; AUMC; MRT; and bioavailability (F), where F = (AUCPO/AUCIV) × 100. Values for AUC and AUMC were calculated by use of the trapezoidal rule with extrapolation to infinity. The percent extrapolated was < 5%.
Results
Mean ± SD plasma concentrations (Figure 1) and pharmacokinetic variables (Table 1) associated with IV and oral administration of the drug were determined. After IV administration, marbofloxacin had a Vd of 1.3 ± 0.32 L/kg and plasma clearance of 0.30 L/h/kg. The harmonic mean for t½ was 4.3 hours after IV administration. Mean residence times were 5.0 and 6.7 hours after IV and oral administration, respectively. After oral administration, Cmax was 1.08 μg/mL and time to reach Cmax (Tmax) was 2.6 hours. Mean oral bioavailability was 90%. None of the macaws had any clinical signs attributable to an adverse drug reaction or adverse effects of repeated blood collection.
Pharmacokinetic variables for marbofloxacin after administration of single oral PO or IV dose of 2.5 mg/kg in 10 healthy blue and gold macaws.
| Pharmacokinetic variables | Administration route | |||||
|---|---|---|---|---|---|---|
| PO | IV | |||||
| Mean ± SD | Median | Range | Mean ± SD | Median | Range | |
| Cmax (μg/mL) | 1.08 ± 0.316 | 1.09 | 0.578–1.65 | NA | NA | |
| Tmax (h) | 2.6 ± 0.8 | 3.0 | 1.0–3.0 | NA | NA | NA |
| AUC (μg•h/mL) | 7.94 2.08 | 7.44 | 5.80–11.9 | 9.41 ± 2.84 | 9.18 | 5.74–16.3 |
| t1/2 (h)* | 3.9 | 4.4 | 1.1–15 | 4.3 | 4.2 | 2.4–11 |
| Clp (L/h/kg) | NA | NA | NA | 0.29 ± 0.078 | 0.27 | 0.15–0.44 |
| Vd (L/kg) | NA | NA | NA | 1.3 ± 0.32 | 1.3 | 0.80–2.0 |
| F (%) | 90.0 ± 31 | 83 | 41–143 | NA | NA | NA |
| MRT (h) | 6.7 ± 2.6 | 6.5 | 3.3–12 | 5.0 ± 1.0 | 4.8 | 3.8–7.3 |
Significantly (P < 0.05) different from values for the other administration routes.
Harmonic mean.
Tmax = Time to reach Cmax. Clp = Total plasma clearance. F = Bioavailability. NA = Not applicable.
Mean ± SD plasma concentrations of marbofloxacin in 10 healthy blue and gold macaws after administration of single PO and IV doses of 2.5 mg/kg. Concentrations were undetectable at later time points.
Citation: American Journal of Veterinary Research 67, 6; 10.2460/ajvr.67.6.947
Mean ± SD plasma concentrations of marbofloxacin in 10 healthy blue and gold macaws after administration of single PO and IV doses of 2.5 mg/kg. Concentrations were undetectable at later time points.
Citation: American Journal of Veterinary Research 67, 6; 10.2460/ajvr.67.6.947
Mean ± SD plasma concentrations of marbofloxacin in 10 healthy blue and gold macaws after administration of single PO and IV doses of 2.5 mg/kg. Concentrations were undetectable at later time points.
Citation: American Journal of Veterinary Research 67, 6; 10.2460/ajvr.67.6.947
Discussion
The pharmacokinetic properties of marbofloxacin have been evaluated in other species including dogs,9,12-14 pigs,15 cattle,6,16 sheep,16 goats,17 horses,18 chickens,19,20 raptors,21 and Eurasian buzzards (Buteo buteo).22,23
The harmonic mean t1/2 of marbofloxacin after IV administration in macaws in the present study was 4.3 hours. Other reported values for t1/2 after IV administration of marbofloxacin have been reported as follows: 4.11 hours in Eurasian buzzards,22 5.3 hours in broilers,20 12 hours in dogs,9 4.2 hours in calves,6 7.2 hours in goats,15 and 4.7 hours in horses.18
A Cmax of 1.08 ± 0.316 μg/mL in the macaws was achieved 2.6 ± 0.84 hours after oral administration. In Eurasian buzzards that received an orally administered dose of 10 mg/kg, Cmax of 3.70 μg/mL was reached 2.92 hours after administration.23 In comparison, Cmax concentration in dogs after an orally administered dose of 2 mg/kg was 1.4 μg/mL after 2.5 hours.9
Dosage recommendations vary according to species. The recommended dosage for dogs is 2.75 mg/kg, PO, every 24 hours, but the dose may be increased to 5.5 mg/kg. A minimum dosage of 2 mg/kg, PO, every 24 hours may be appropriate for control of most susceptible infections in chickens.20 Results of studies22,23 in buzzards suggest that marbofloxacin should be administered at a dosage of 2 mg/kg, IV, every 12 hours or 10 mg/kg, PO, every 24 hours.
On the basis of our results, marbofloxacin administered at 2.5 mg/kg, PO, every 24 hours may be effective for the treatment of infections caused by susceptible bacteria in macaws, depending upon the MIC of the target pathogen. This dosing frequency was derived on the basis of the Cmax:MIC ratio of suspected avian pathogens with an MIC of 1.0 and on the breakpoint concentration of 1.0 μg/mL for susceptible pathogens as determined in dogs and cats by the Clinical and Laboratory Standards Institute; those values would yield a Cmax:MIC ratio of approximately 10.0. Marbofloxacin has bactericidal activities against a wide range of gram-negative and gram-positive organisms and may be useful for treatment of bacterial infections of the skin, urinary tract, and soft tissues in blue and gold macaws.
ABBREVIATIONS
| HPLC | High-performance liquid chromatography |
| AUC | Area under the concentration-versus-time curve |
| AUMC | Area under the first moment curve |
| MRT | Mean residence time |
| Vd | Volume of distribution at steady state |
| t1/2 | Terminal half-life |
| Cmax | Maximum plasma concentration |
| MIC | Minimum inhibitory concentration |
Zeniquin, Pfizer Animal Health, Exton, Pa.
Daily Select Premium large bird food, Pretty Bird International Inc, Stacy, Minn.
Marbocyl FD, Vétoquinol International, Cedex, France.
Synergi Hydro RP (150 × 2.0 mm, 4 μm, 80 Å), Phenomenex, Torrance, Calif.
LCQduo, ThermoFinnigan, San Jose, Calif.
WinNonlin, version 3.1, Pharsight, Mountain View, Calif.
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