ObjectiveTo establish a method for determining the concentration of gatifloxacin in rabbit ocular tissue and compare the ocular pharmacokinetics of 0.3% gatifloxacin eye gel after a single and multiple topical instillations in rabbits.

MethodsNinety-four healthy New Zealand rabbits were selected.Ten rabbits were randomly selected without any treatment for blank tissue collection, and the remaining 84 rabbits were randomly divided into a single-dose group (36 rabbits) and a multiple-dose group (48 rabbits) equally between males and females using a random number table.The left eye was taken as the experimental eye.The single-dose group was given one drop of 0.3% gatifloxacin eye gel into the left eyes, and the rabbits were divided evenly into six subgroups.In each subgroup, tear specimens and blood specimens were collected at 0.5, 1, 3, 5, 7, 10 hours after gel application, then cardiac blood samples were taken, after which animals were sacrificed immediately to collect ocular tissue including aqueous humor, conjunctiva, cornea, sclera, iris-ciliary body, lens, vitreous body, retina, and choroid.The multiple-dose group was given 1 drop of gatifloxacin ophthalmic gel in the left eye three times a day.At 0.5 hour after the first administration days 4 and 6, and 0.5, 1, 3, 5, 7, and 10 hours after the first administration on day 7, the cardiac blood sampling and ocular tissue collection were performed.The methanol precipitation protein method was used to pretreat samples, and the concentration of gatifloxacin in rabbit plasma and eye tissue was measured and calculated by high-performance liquid chromatography-tandem mass spectrometry method to obtain pharmacokinetic-related parameters such as peak concentration (C _max), peak time (T _max), and area under curve (AUC).The mobile phase was a methanol-0.1% acetic acid aqueous solution (volume ratio=70∶30), and a positive ion multiple reaction detection mode was used.Ciprofloxacin was used as the internal standard, the selectivity, standard curve and lower limit of quantification, accuracy and precision, extraction recovery rate, matrix effect, and stability of the method were validated in accordance with the 9012 Guidelines for Validation of Quantitative Analysis Methods for Biological Samples in Chinese Pharmacopoeia ( 2020 edition).Combined with the minimum inhibitory concentration (MIC ₉₀) of gatifloxacin on common ocular infectious bacteria, C _max/MIC ₉₀ and AUC/MIC ₉₀ were calculated.The study protocol was reviewed and approved by the Animal Ethics Committee of Shenyang Xingqi Pharmaceutical Co., Ltd.(No.XQ-2016-011).

ResultsGatifloxacin has a good linear relationship in various eye tissues and plasma.The between-run precision in corneal tissue is within the range of -1.5%-6.0%, and the daytime precision was not greater than 15%.The extraction recovery rate in corneal tissue ranged from 92.0% to 94.8%, and the precision of the matrix effect at low, medium, and high concentrations calculated by internal standard normalization was not greater than 3.3%.After a single topical instillation, gatifloxacin reached a high concentration in anterior and posterior segment ocular tissues and its distribution ranked in order from the highest to the lowest by AUC _0-t as follows, tears, cornea, conjunctiva, iris-ciliary body, sclera, aqueous humor, choroid, retina, lens and vitreous body, with the C _max of 94.90 μg/g, 7.34 μg/g, 3.65 μg/g, 1.81 μg/g, 1.75 μg/g, 1.31 μg/ml, 0.86 μg/g, 0.53 μg/g, 0.13 μg/g and 0.07 μg/ml, respectively.T _max was 1 hour in all ocular tissues except in the lens, choroid, and vitreous body fluid, where T _max was 0.5 hour.There was no significant difference among the concentrations of gatifloxacin in ocular tissues at 0.5 hour on days 4, 6 and 7 after multiple dosing ( P>0.05), and the AUC _0-t in the cornea, conjunctiva, and sclera was approximately 2.04, 2.12, and 2.32 times that of the single dosing.The concentration of gatifloxacin released into the systemic circulation after single and multiple dosing was less than 25.00 ng/ml.For both Staphylococcus aureus and Staphylococcus epidermidis, pharmacokinetic/pharmacodynamics in the conjunctiva, cornea, sclera, iris-ciliary body, aqueous humor, and choroid were satisfied with C _max/MIC ₉₀≥10 and AUC/MIC ₉₀≥30 after continuous administration of gatifloxacin ophthalmic gel.

ConclusionsA rapid and sensitive method for measuring gatifloxacin concentration in ocular tissues is successfully constructed.Gatifloxacin ophthalmic gel administered three times a day for three days can achieve stable concentrations in ocular tissues, and the concentration of gatifloxacin in ocular tissues is increased compared with a single dose.Effective treatment of common bacterial infections of the conjunctiva, cornea, sclera, and iris-ciliary body can be achieved with topical application of gatifloxacin ophthalmic gel.