Buffered isotonic solutions maintain both a stable pH and an osmotic pressure similar to that of physiological fluids, such as blood and tears.
These solutions are commonly used in pharmaceutical and medical applications, particularly for parenteral (injection), ophthalmic, and nasal preparations, to minimize irritation and prevent damage to cells and tissues upon administration.
Key Properties of Buffered Isotonic Solutions:
1. Buffering capacity:
These solutions contain a buffer system that resists changes in pH when small amounts of acid or base are added, ensuring the stability, efficacy, and safety of active pharmaceutical ingredients (APIs).
Common buffer systems include phosphate, acetate, and citrate buffers.
2. Isotonicity:
Buffered isotonic solutions have an osmotic pressure (~290 mOsmol/kg) similar to physiological fluids, preventing damage to cells (e.g., swelling from hypotonic solutions or shrinkage from hypertonic solutions).
Substances like sodium chloride, glucose, or mannitol are often added to adjust the osmotic pressure.
Preparation of Buffered Isotonic Solutions:
1.Select a Buffer System:
Choose a buffer with a pKa close to the desired pH.
2.Calculate Buffer Concentrations:
Use the Henderson-Hasselbalch equation to calculate the appropriate concentrations of the weak acid and its conjugate base.
3.Dissolve Buffer Components:
Weigh and dissolve the buffer components in a suitable solvent (typically water).
4.Adjust pH:
If necessary, adjust the pH using small amounts of strong acid (e.g., HCl) or base (e.g., NaOH).
5.Add Isotonicity-Adjusting Substance:
Calculate and dissolve the required amount of isotonicity-adjusting substance (e.g., sodium chloride) to achieve the desired osmotic pressure.
6.Measure Osmolality:
Use an osmometer to confirm that the solution's osmolality is within the desired range.
7.Transfer and Store:
Transfer the solution to a suitable container and store it under appropriate conditions.