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In Vitro Iris and Corneal Uptake and Washout of 1% Lidocaine Hydrochloride

Nicole J. Anderson, MD; Wendell D. Woods, PhD; Terry Kim, MD; David E. Rudnick, MA; Henry F. Edelhauser, PhD

Arch Ophthalmol. 1999;117:225-232.

Objectives  To characterize the uptake, washout, and metabolism of lidocaine hydrochloride in the iris/ciliary body and cornea.

Methods  Iris/ciliary body uptake of lidocaine hydrochloride was measured by incubating human and rabbit irides in radiolabeled carbon 14–1% lidocaine hydrochloride for 2 to 60 minutes. Washout was determined by incubating the iris in ¹⁴C–1% lidocaine hydrochloride for 5 minutes and transferring the iris to a series of wells. The wells contained a common intraocular irrigating solution of essential ions, glucose, and glutathione buffered with bicarbonate (an enriched balanced salt solution [BSS PLUS]), which is similar to aqueous humor. Corneal uptake was measured by exposing the endothelial surface to ¹⁴C–1% lidocaine hydrochloride for 5 or 15 minutes. Corneal washout was performed after 5-minute exposure to ¹⁴C–1% lidocaine hydrochloride using a 2-chambered diffusion apparatus. Samples of the iris, cornea, and BSS PLUS washout solution were analyzed by high-performance liquid chromatography and liquid scintillation spectrometry.

Results  In vitro iris/ciliary body uptake of ¹⁴C–1% lidocaine hydrochloride follows a logarithmic curve, with 50% to 60% of maximum lidocaine hydrochloride uptake present at 5 minutes. There was no difference in uptake between human, albino rabbit, and pigmented rabbit irides. Washout of lidocaine from the iris occurs with a half-life of 8 to 9 minutes. Corneal uptake of lidocaine was greater after incubation for 15 vs 5 minutes. The washout of lidocaine from the cornea had a half-life of 5 minutes. Results of high-performance liquid chromatography confirmed that there were no metabolites or breakdown products in the iris, cornea, or washout solution.

Conclusions  Lidocaine is taken up quickly by the iris/ciliary body and cornea and rapidly removed from these tissues after BSS PLUS washout. Irrigation during phacoemulsification seems to limit lidocaine exposure to the ocular tissues, resulting in a short duration of anesthesia. Lidocaine is not metabolized or broken down by the iris or cornea during this short period.

From the Departments of Ophthalmology, Emory University School of Medicine, Atlanta, Ga (Drs Anderson, Woods, and Edelhauser and Mr Rudnick), and Duke University School of Medicine, Durham, NC (Dr Kim). The authors have no commercial, proprietary, or financial interest in the products or companies described in this article.