Ocular pharmacokinetics of calcium, chloride and sulphate ions after instillation in the rabbit

The ionic environment of the eye is involved in major biochemical processes which are essential for preserving the integrity of cornea and lens. The purpose of the present study was to determine the intra-ocular penetration and the pharmacokinetic parameters of calcium, chloride and sulphate ions in the cornea, iris-ciliary body (ICB) and lens, after administration by instillation in the rabbit eye. In order to extrapolate our results to the processes occurring in man, we followed a precise instillation protocol using a low volume (5 microliters) of 45Calcium, 36Chloride and 35Sulphate, which is less than the lacrimal volume determined during the palpebral closing and performing manual blinking at a frequency of 2 min-1. The results indicate an immediate trans-corneal permeability and a rapid ocular distribution of these ions. We observe that, relative to dose, an important percentage of calcium (67.20 per cent) was entrapped in the cornea; this parameter was less important for chloride (10.19 per cent) and for sulphate ions (3.25 per cent). These values are in agreement with those predicted theoretically for trans-corneal penetration by such compounds. On the other hand, the total degrees of penetration by chloride and sulphate ions in ICB (1.40 per cent and 0.90 per cent, respectively) and lens (0.35 per cent and 0.41 per cent, respectively) are quite similar. Calcium retention is much higher in these tissues (25.39 per cent in ICB and 16.03 per cent in lens).(ABSTRACT TRUNCATED AT 250 WORDS)