Tonicity agents sodium chloride

TONICITY AGENTS OTHER THAN SODIUM CHLORIDE... 

Step 4 From Step 3, 0.231 g of sodium chloride is required to make the preparation isotonic. But the prescription calls for boric acid as the tonicity agent. Boric acid has an E value of 0.52. This means that 1% boric acid is osmotically equivalent to 0.52% NaCl or 1 g of boric acid is equivalent to 0.52 g of NaCl. 

Hypotonic ophthalmic solutions or suspensions can be rendered isotonic by the addition of tonicity agents such as sodium chloride, potassium chloride, dextrose, glycerol and buffering salts. As with other adjuvants, the formulator should give due consideration to possible interactions between the tonicity agent and other components of the formulation, including the drug itself. 

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