- 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 essential in pharmaceutical and medical applications (e.g., injections, ophthalmic, and nasal preparations) to minimize irritation and prevent tissue damage during 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.
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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.
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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).
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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.
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7) Transfer and Store:
- Transfer the solution to a suitable container and store it under appropriate conditions.
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