Preservatives

Question 1

Chelators/Anticoagulants

Answer 1

eg EDTA and citrate

• Forms complex with reactive metals that aid in bacterial growth and facilitate oxidative reactions,
• Inhibit bacteria/mold/yeast,
• EDTA and citrate - has medical uses- forms a complex with blood calcium -anticoagulant
• EDTA forms irreversibly

Question 2

How do organic acids exhibit a preservative effect

Answer 2

• Act by disrupting microbial metabolic pathways intracellularly, therefore most active at low, undissociated pH
• Alteration of Ph affects enzyme function
• eg Sorbic acid
• Benzoic acid(food preservation and antiseptic)

Question 3

Oxidants and antioxidants

Answer 3

• Oxidants- source of highly reactive free radicals
  
  • eg Hydrogen peroxide
• Antioxidants - reduce oxidation of active ingredient by free radicals(prevent oxidation and does not kill microbes)
  
  • eg Ascorbic acid, NHT, BHA,

EDTA is added to chelate metal ions to facilitate oxidation reactions

Question 4

Alcohols and parabens

Answer 4

Alcohols-act by dehydrating environment
eg Chlorbutanol, Phenol, Benzyl alcohol

Parabens- effective antiseptic and preservative
susceptible to decomp, risk of hypersensitivity
eg Methyl paraben, Ethyl paraben, Propyl paraben

Question 5

Heavy metals act by…

Answer 5

Irreversibly binding to key enzymes

Organomercuric compounds
eg Thimerosal, Phenylmercuric nitrate

Polymers
eg Povidone (synthetic, water soluble non-ionic that can absorb 40% own weight in water, used in WW2 as plasma expander, used stopped due to stimulation of histamine response)

Question 6

Surfactants are

Answer 6

• Bactericidal
• Ionic detergents, rupture cell walls or junctions

Question 7

Types of surfactants

Answer 7

• Biguanides - 1st line DM2 agents (Metformin)
• eg polyhexamethylene biguanide (PHMB)
• polyaminopropyl biguanide (PAPB)
• -Chlorhexidine
• Alexidine
• Amidoamines
  
  • eg MAPD
• Quaternary Ammonium Compounds
  
  • -effective at neutral pH
  • -Adsorbed onto surface of glass/plastic containers
  • eg Benzalkonium chloride-most common in ophthalmic drops
  • eg Polyquaternium (quats)

Question 8

What are disappearing eye drops

Answer 8

They are inactivated in light or different pH

Question 9

Name an example of a self preserved ophthalmic drop

Answer 9

Moxifloxacin

Question 10

Adverse effects of preservatives

Answer 10

• Hypersensitivity
• Local irritant
  
  • Skin, lungs, eyes, GIT, other mucous membranes
• Asthma
  
  • EDTA carries risk of dose-related bronchoconstriction
• Neurological toxicity
  
  • eg parabens are neurotoxic in rats
• Cancer