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F. Giansanti, M. Ramazzotti, L. Vannozzi, D. Degl'Innocenti, M. Giuntoli, U. Menchini; Intravitreal Infliximab Clearance: Different Sampling Techniques and Assay Methods. Invest. Ophthalmol. Vis. Sci. 2009;50(13):5024.
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Infliximab is a human-mouse chimaeric IgG1 antibody specifically designed to inhibit the active soluble TNF-. Due to the systemic administration route, its positive effects on uveitis is usually coupled to serious side effects due to antigenicity and to a general immuno-depression. In the past we demonstrated the safety of intravitreal infliximab in a rabbit model from clinical, functional and microscopic points of view. We also proposed a novel vitreous micro-sampling technique consisting in the aspiration of very reduced amounts of vitreous samples (10-15 µl) from anesthetized living animals, with benefits from both ethical and economical points of view. In this new work a 1.5 mg dose of infliximab was injected in the vitreous of anesthetized rabbit. Vitreous clearance of the drug was evaluated with standard and microsampling technique.
Thirtysix rabbits were used for the study. 1.5 mg of infliximab was injected in the vitreous of each animal. Samples were taken at consecutive times ranging from 30 min to 40 days with both standard and micro- sampling methods. For measurements, we used a comparative multi-assay approach
Both sampling methods agreed in determining a mono-exponential decrease starting at day 3-4, with an half life of approximately 6-7 days and reaching a quasi-zero level at day 35-40. During the initial lag phase, micro-samplings from different vitreous portions detected lacunae with heterogeneous infliximab concentration. A thermal vitreous liquefaction allowed us to observe that infliximab was retained within the eye for at least three days prior to decrease, during which it distributed in the vitreous. The micro-sampling method proved to give details on drug distribution not achievable by the classic method while maintaining a comparable accuracy. For measurements, we used a comparative multi-assay approach. ELISA proved to be the most sensitive and less sample-expensive technique, the perfect candidate for analysing micro-samples. Western blot showed the absence of cross-reacting material and, more importantly, that infliximab kept its integrity during the time course, an important result in term of drug efficacy. The dot blot technique proved to be reliable for the rapid quantification of infliximab, surely faster and less tricky than ELISA but with poor sensitivity.
Infliximab has a vitreous half life of approximately 6-7 days. Both sampling methods agreed in determining vitreous half life of the drug.
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