Isotonic pharmaceutical buffers

Some discomfort and possible injury can be avoided in using pharmaceutical solutions that are intended for parenteral injection or for application to delicate membranes of the body if these solutions are routinely adjusted to approximate isotonicity with body flixid. (At 37°C the standard is an 0.90% sodium chloride solution.) The Tables 3.14 and 3.15 summarize recent studies on isotonic buffers at 25°C and 37°C. A 1.77% boric acid solution is isotonic with 0.9% NaCl and has a pH of 4.96 at 25°C and 4.85 at 37°C (Cutie and Sciarrone, 1969). 

Several buffers have been studied at 25° C in isotonic saline (solutions adjusted to 7=0.16 by adding NaCl). In such solutions, equimolal ratios of Tris and Tris-HCl (each 0.05 m) gave a pH of 8.225, while for Bis-tris and Bis-tris-HCl (each 0.05 m) it was 6.647. Acetic acid (0.05 m) and sodium acetate (0.05 m) gave pH 4.637, and for 0.05 m KH2 citrate it was 3.683 (Durst, 1970). All values are within 0.005 pH units of predictions from the NaCl-free solutions, using the Debye-Hiickel equation. 

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Buffer solutions that are isosmotic with respect to some standard, typically chosen such that suspended cells will neither shrink nor expand. Sodium chloride solutions (0.90% weight/volume or 0.155 M) at 37°C is often used to represent physiological conditions. These buffer systems are also important in studies of intact cells and membranal organelles likewise, many pharmaceutical formulations must be prepared as isotonic solutions. Most enzyme-catalyzed reactions are affected by ionic... 

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