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


  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.
Last updated 2019-07-18

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