The pH of antibiotic vitreous infusion combinations: a potential cause of retinal toxicity.

Experiments were undertaken to measure the pH of solutions of commonly used intravitreal antibiotics in various irrigating solutions to determine whether a change in pH might be a factor in antibiotic-induced retinal toxicity. Such retinal toxicity has been particularly damaging when solutions of gentamicin have been used. The pHs of the following solutions were measured: gentamicin, amikacin, methicillin, tobramycin, and vancomycin, combined with balanced salt solution (BSS) PLUS (bicarbonate buffer), BSS (citrate/acetate buffer), and lactated Ringer's solution (lactate buffer). Each of these antibiotics induced a concentration-dependent decrease in pH of the solutions; gentamicin, amikacin and tobramycin produced the largest shifts. The results also demonstrated that BSS PLUS acts as the strongest buffer and lactated Ringer's as the weakest. We conclude that it is important to determine the pH of intraocular antibiotic irrigating solutions, not just the pH of the antibiotics.