Methods of adjusting tonicity and pH values of some drugs and substances.

Abstract

Lachrymal fluid is isotonic with blood having an isotonicity valve corresponding to that of a 0.9% Nacl solution. Ideally, an ophthalmic solution should have this isotonicity valve, but the eye can tolerate isotonicity valves as low as that of a 0.6% Nacl solution and as high as that of a 2% Nacl solution without marked discomfort. Some ophthalmic solutions are necessarily hypertonic in order to enhance absorption and to provide a concentration of the active ingradient(s) strong enough to exert a prompt and effective action. The amount of such solution used is small because, on administration, the dilution with lachrymal fluid takes place rapidly with minimal discomfort from the hypertonicity which is only temporary. However, any adjustment toward isotonicity by dilution with tears is negligible where large volumes of solutions are used as collyria to wash the eyes. It is, therefore, important that solutions used for this purpose be approximately isotonic.