Influence of Topical Anesthesia on Tear Dynamics and Ocular Drug Bioavailability in Albino Rabbits

Ocular Pharmacokinetics

“…Studies with fluorescein show that the increase in penetration that can be achieved is limited to 50%-100%, and that this maximum rise can be achieved with solutions which are only slightly viscous (ADLER et al 1971;PATTON and ROBINSON 1975). Most probably this is a result of greater initial saturation of the tear film, not a slower rate of washout (AoLERet al 1971;SUGAYAand NAGATAKI 1978).…”

“…The turnover rates in rabbits and humans are on average very much the same, therefore. Considerably larger values are found in the stimulated eye (SIEG and ROBINSON 1977) or on deviations from physiological pH (CONRAD et al 1978), but the flow returns to baseline after topical anesthesia (PATTON and ROBINSON 1975). The position of the animal's head, when it is under anesthesia, has a noticeable effect on drainage (SIEG and ROBINSON 1974).…”

“…The tearing that occurs from painful stimuli can wash substances out of the conjunctival sac within a minute (MAURICE 1971). On the other hand, tear flow is heavily suppressed during general anesthesia (KRUPIN et al 1977) in humans and is lowered by local anesthesia in rabbits (PATTON and ROBINSON 1975). According to MURAl (1976), the turnover rate drops by about one-half when the eyes are closed.…”

“…In the rabbit, PATTON and ROBINSON (1975) estimated the average flow rate of tears to be 0.66 III min -1, and LONGWELL et al (1976), who directly cannulated the drainage duct, found a value of 0.78 III min -1. Since the total volume of lacrimal fluid is 7.5 Ill, this flow rate should lead to a loss constant of 6 h -1 for substances dissolved in the tears, and a figure of 5 h -1 for technetium loss was determined experimentally by CHRAI et al (1973).…”

Ophthalmic and anesthetic evaluation of topical 1% tetracaine and 0.5% proparacaine in dogs

“…According to Patton and Robinson (1975), decreased tear production afforded by the action of local anesthetics is responsible for increasing the bioavailability of the drug in the tissues of the cornea. This would be a possible explanation for the increase in the time of anesthetic action found in the dosage of two drops.…”