Additives

Describe the mechanisms of action and potential adverse effects of buffers, anti-oxidants, anti-microbial and solubilizing agents added to drugs

Additives are components of a drug preparation which do not exert the pharmacological effect.

Additives include:

• Preservatives
  • Benzyl alcohol
    • Antimicrobial when > 2%
    • Can be used as a solvent when > 5%
    • Toxic

• Antioxidants
  • Sulfites
    • Hypersensitivity
    • Neurotoxic if given intrathecally

• Solvents
  • Water
    Appropriate for dissolving polar molecules.
  • Non-aqueous solvents
    Used to dissolve non-polar molecules, or to produce more stable preparations of semi-polar molecules. Examples include:
    • Propylene glycol
      • Hypotension
      • Arrhythmia
        With rapid injection.
      • Pain on injection
      • Thrombophlebitis
    • Mannitol
      • Diuresis
    • Soybean oil
      • Pain on injection
      • Allergy

• Emulsion
  Formed when drops of a liquid are dispersed throughout another liquid in which it is immiscible. Emulsions are:
  • Unstable
    Emulsifiers are used to enhance stability.
  • Prone to contamination
    Due to the water component.
  • Prone to rancidity
    Due to the oil component.

• Buffers
  Maintain pH in a particular range in order to:
  • Maximise stability
    Preserve shelf life.
  • Maintain solubility
  • Maximise preservative function

References

1. MacPherson RD. Pharmaceutics for the anaesthetist. Anaesthesia. 2001 Oct;56(10):965-79.
2. Petkov V. Essential Pharmacology For The ANZCA Primary Examination. Vesselin Petkov. 2012.