Vehicles, Additives, and Importance of Isotonicity

• Vehicles, Additives, and Importance of Isotonicity play a crucial role in pharmaceutical formulations by ensuring drug solubility, stability, and patient acceptability.
• Vehicles and Additives also help maintain osmotic balance to prevent irritation or tissue damage.

Vehicles

• The medium in which the drug is dissolved or suspended.
• Common vehicles include:
  1. Water for Injection (WFI): Highly purified water used as a solvent.
  2. Saline Solutions:9
  3. Glucose Solutions: Used for energy and as a solvent.
  4. Lactated Ringer’s Solution: Contains electrolytes and is used for fluid replacement.
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Additives

• Substances added to enhance the stability, solubility, or administration of the drug, such as:
  1. Preservatives: To prevent microbial growth (e.g., benzyl alcohol).
  2. Buffers: To maintain pH (e.g., phosphate buffers).
  3. Stabilizers: To prevent degradation (e.g., antioxidants like ascorbic acid).
  4. Surfactants: To improve solubility or reduce surface tension.
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Importance of Isotonicity

• Isotonicity ensures that the parenteral solution has the same osmotic pressure as bodily fluids, preventing:
• Maintaining isotonicity is crucial to avoid tissue irritation, pain at the injection site, and systemic complications such as hemolysis or edema.
  1. Cell Lysis: From hypotonic solutions causing water influx.
  2. Cell Shrinkage (Crenation): From hypertonic solutions causing water efflux.
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