Iontophoresis-gentamicin delivery into the rabbit cornea, using a hydrogel delivery probe

Purpose. To evaluate the efficacy of penetration of gentamicin into the cornea of rabbits using iontophoresis with a hydrogel-gentamicin containing probe. Methods. Eight of 10 groups (groups 3-10) of 6 rabbits (one eye per rabbit), underwent corneal iontophoresis using soft stable hydroxyethyl methacrylate hydrogel discs (80% water content) loaded with gentamicin sulphate which were mounted on an iontophoresis probe. The studied current intensities were 0, 0.1, 0.3 and 0.6mAmp, and the durations of iontophoresis were 10 and 60sec. Two control groups received 1.4% topical drops of gentamicin every 5 min for 1hr (group 1) or sub-conjunctival injection of 10 mg gentamicin (group 2). Following sacrifice, aqueous humour was taken, corneas were excised, and gentamicin concentration was determined in aqueous humour and cornea samples. Results. Post-iontophoresis, the concentration of gentamicin in the corneas ranged from high (88.60±38.64 μg ml^-1) to very low (0.10±0.89 μg ml^-1). Both the control groups and those rabbits treated with current intensity of 0.1mAmp or greater obtained therapeutic gentamicin levels in the corneas. Use of iontophoresis for 60sec or current intensity greater than 0.1mAmp obtained corneal gentamicin levels not different from sub-conjunctival injection. Application of current intensity of 0.1mAmp or greater gave corneal gentamicin concentrations comparable to topical application of the drug, except when 0.6mAmp were used for 60sec (p=0.05). Increasing current intensity or duration of iontophoresis significantly increased (p=0.001 for both) gentamicin penetration into the cornea. Current intensity had more influence (Beta²=0.40) than duration (Beta ²=0.13) on drug penetration. A significant interaction was found between the duration of iontophoresis and the current intensity. Very small or no concentrations of the drug were discovered in the anterior chambers of rabbits. Conclusions. Iontophoresis using hydrogel-gentamicin probe may deliver therapeutic concentrations of gentamicin into the cornea.