Topical bupivacaine and proparacaine: a comparison of toxicity, onset of action, and duration of action.

Bupivacaine is a local ocular anesthetic with a long duration of action when administered by retrobulbar injection. To determine the potential for the use of bupivacaine as a topical ocular anesthetic, the onset and duration of action and toxicity of various concentrations of bupivacaine were studied after instillation in rabbit eyes. The onset and duration of action were not significantly different from that of topical 0.5% proparacaine. Increasing the pH of the bupivacaine solution from 5.7 to 6.5 nearly doubled the duration of action, but the increase was not sufficient to be clinically important. Slit lamp biomicroscopic examination and scanning electron microscopy showed that bupivacaine was less toxic to the corneal epithelium than 0.5% proparacaine. Healing after keratectomy was significantly more rapid in eyes treated with 0.75% bupivacaine, compared with eyes treated with 0.5% proparacaine. These results suggest that bupivacaine may be less toxic to the corneal epithelium than proparacaine and could be clinically useful for topical ocular anesthesia, particularly if pharmacologic modifications can increase the duration of anesthesia provided by this drug.