Formulation Factors to Consider

Solution pH

The physiologic pH of blood and tears is approximately 7.4. Thus, from a comfort and safety standpoint, this would be the optimal pH of ophthalmic and parenteral solutions. This may not be possible, however, from a perspective of solubility, chemical stability or therapeutic activity. Thus, some compromise must be made and product stability must be considered paramount.

When a formulation is administered to the eye, it stimulates the flow of tears. Tear fluid is capable of quickly diluting and buffering small volumes of added substances, thus the eye can tolerate a fairly wide pH range. Ophthalmic solutions may range from pH 4.5 - 11.5. But the useful range to prevent corneal damage is 6.5 to 8.5.

Once we have determined the optimal pH of a product, we need a mechanism for adjusting and maintaining the pH of the solution.