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Buffers in Pharmaceutical and Biological Systems and Buffered Isotonic Solutions

Many pharmaceutical practices use buffer solutions, especially when formulating ophthalmic solutions.

Biological buffer systems

An average pH of 7.4 is maintained in the blood and in that Plasma contains buffers consisting of carbonate and bicarbonate as well as acid and alkali sodium salts of phosphoric acid. A plasma protein that behaves like an acid in the blood can combine with a base to act as a buffer. Hemoglobin/oxyhemoglobin and acid/alkali potassium salts of phosphoric acid make up the two buffer systems of the erythrocytes.

At body temperature with an ionic strength of 0.16, the dissociation exponent pK1 of carbonic acid in the plasma is about 6.1. Forcarbonic acid/bicarbonate buffer of the blood, the buffer equation can be written as,


H2CO3 is the blood represents CO2 in blood as dissolved CO2. In normal blood plasma with a pH of 7.4, the ratio of bicarbonate to carbonic acid is,


Or,

Lacrimal fluids - Researchers have discovered that lacrimal fluid has a moderate buffer capacity, to the point that it can be diluted 1:15 using neutral distilled water. There is a pH range of 7 to 8 for tears, with a pH of about 7.4. According to consensus, eye drops that have a pH between 4 and 10 will not harm the cornea. Below pH 6.6 and above pH 9.0, though, discomfort and tears may occur.

Urine - An adult's 24-hour urine collection averages approximately pH 6.0, but it can range from 4.5 to 7.8. Hydrogen ions are excreted by the kidneys when urine pH falls below normal values. Conversely, the kidneys function by reabsorbing hydrogen ions when the urine's pH is higher than 7.4.

Pharmaceutical buffers

Many pharmaceutical practices use buffer solutions, especially when formulating ophthalmic solutions. A wide variety of buffer solutions is available today and phosphate-buffered saline (PBS) is one of the most common biological buffers. Na2PO4 and sodium chloride (NaCl) are contained in phosphate-buffered saline. A mixture of KCl, phosphoric acid, calcium chloride, magnesium sulfate, and monobasic potassium phosphate may also be present.

The pH of pharmaceutical products is usually adjusted using buffering systems for two reasons: to ensure maximum stability and to maintain that pH within physiological limits. The pH of the body fluids is usually substantially changed by pharmaceutical solutions since they usually have low buffer capacity to prevent overpowering the body's buffer system. Pharmaceutical solutions are normally buffered with buffer concentrations within the range of 0.025 to 0.050 M, whereas buffer capacities are usually between; 0.01 to 0.1. Many pharmaceutical buffers, such as acetate, phosphate, citrate, and borate, are derived from substances naturally found in the body. It is best to choose a pharmaceutical buffer with a pH greater than pKa when choosing one. Buffers in pharmaceuticals are present in four forms such as,
  1. Parental buffers
  2. Solid dosage forms
  3. Semisolid formulations
  4. Ophthalmic products

Buffered Isotonic Solutions

Pharmaceutical solutions that are intended to be applied to delicate body membranes must also have an equivalent osmotic pressure as the fluids in the body. An isotonic solution is not accompanied by swelling or contraction in the tissues it contacts. Isotonic solutions can be injected into the eye, the nasal passages, the blood, and other body tissues. The isotonic solution of sodium chloride is a familiar pharmaceutic preparation of this kind. A small amount of blood mixed with various toxicities of aqueous sodium chloride solutions illustrates the need for isotonic solutions when applied to delicate membranes.
  1. Isotonic - 0.9 g of NaCl per 100 mL maintains the normal size of cells if blood is added to the solution. Solution and red blood cell contents are essentially the same in terms of salt concentration and osmotic pressure
  2. Hypertonic - The red blood cells floating in a NaCl solution of 2.0% are hypertonic by passing through their cell membranes, making an effort to dilute the nearby salt solution. Cells shrink as a result of this outward flow of water and become wrinkled or crenated.
  3. Hypotonic - Blood that is mixed with 0.2% NaCl solution or distilled water causes the blood cells to swell and eventually burst, releasing hemoglobin. The concentration of salt in this scenario is understood as being concerning the content of the blood cells. Haemolysis is a term used to describe this process.
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Ankur Choudhary is India's first professional pharmaceutical blogger, author and founder of Pharmaceutical Guidelines, a widely-read pharmaceutical blog since 2008. Sign-up for the free email updates for your daily dose of pharmaceutical tips.
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