Intracameral anesthesia: in vitro iris and corneal uptake and washout of 1% lidocaine hydrochloride.
OBJECTIVE
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 halflife 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.
Anderson
N J
NJ
Department of Ophthalmology, Emory University School of Medicine, Atlanta, GA, USA.
Woods
W D
WD
Kim
T
T
Rudnick
D E
DE
Edelhauser
H F
HF
D000772:Anesthesia, Local; D000779:Anesthetics, Local / Q000378:metabolism / Q000493:pharmacokinetics*; D000818:Animals; D000867:Anterior Chamber / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D002924:Ciliary Body / Q000378:metabolism*; D003315:Cornea / Q000378:metabolism*; D006207:Half-Life; D006801:Humans; D007498:Iris / Q000378:metabolism*; D008012:Lidocaine / Q000378:metabolism / Q000493:pharmacokinetics*; D008875:Middle Aged; D011817:Rabbits
D000779:Anesthetics, Local; D008012:Lidocaine