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Infections > Antimicrobial preservatives > Flashcards

Antimicrobial preservatives Flashcards

1
Q

What is the purpose of antimicrobial preservatives?

A

To prevent and inhibit the growth of micro-organisms which could cause an infection in the patient taking the medication or cause degradation of the medication.

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2
Q

What is not the purpose of antimicrobial preservatives?

A

Cover up poor manufacturing processes.

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3
Q

What are the four main functions of antimicrobial preservatives?

A
  1. Reduce the risk of spoilage (excipients can be metabolized by microbes)
  2. Kill any low level contaminants still remaining the preparation
  3. Some micro-organisms may survive sterile preparation, resistant to aseptic techniques.
  4. Loss of profits
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4
Q

What bacterium can metabolise preservatives?

A

Gram negative bacterium when the preservative concentration is below a certain level.

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5
Q

What are the observable effects of microbial attack on pharmaceutical
products?

A

Discolouration
Loss of viscosity
Acidic or basic metabolites changing the pH of the product
Change to the smell or taste
Gaseous metabolites may be seen as trapped bubbles within viscous formulations

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6
Q

When an emulsion is broken down what are some of the observable effects?

A

The metabolism of the surfactants will reduce stability between the water and oil globules which will cause the creaming of the oil globules. This then reduces the pH and encourage the coalescence of the globules causing cracking. . Fatty acids and their
ketonic oxidation products will provide a sour taste and unpleasant smell, whilst bubbles of gaseous metabolites may be visible, trapped in the product, and pigments may discolour the product.

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7
Q

Which type of emulsions are susceptible to antimicrobial attack?

A

Oil in water emulsions. The preservative tends to partition in the oil phase and therefore contaminates attack the aqueous phase where there is little presence of contaminants.

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8
Q

What therapeutics are prone to anti-microbial attack?

A

Morphine, atropine, paracetamol and steroid esters

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9
Q

What Humectants are prone to anti-microbial attack?

A

Glycerol/Sorbitol

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10
Q

What are the 7 factors affecting anti-microbial spoilage?

A

Types, and size of contaminant inoculum
Nutritional factors
pH
Moisture content
Redox potential
Storage temperatures
Packaging design

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11
Q

How do micro-organisms survive within pharmaceutical products?

A

Ingredients become more resistant to heat sterilisation if polymers are present such as gelatin.
Adsorption onto naturally occurring particulate material may aid
establishment and survival in some environments.

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12
Q

What sort of pharmaceutical containers has Pseudomonas taken advantage of?

A

Pseudomonas can grow in solutions of QAC antiseptics and chlorohexidine resulting in the contamination of products.

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13
Q

What are some of the requirements of a preservative?

A

be able to kill rapidly all microbial
contaminants (broad spectrum) as they
enter the medicine.
* not be irritant or toxic to the patient.
* be stable and effective throughout the life of
the medicine.
* be selective in reacting with the
contaminants and not the ingredients of the
medicine.
* Effective at low concentrations
* Effective over wide pH range
* Does not interact with formulation
ingredients

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14
Q

What is benzoic acid used for?

A

It is used as a preservative for oral and topical formulations

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15
Q

What strength of biguanides are used as a preservative?

A

0.0025% used as a solution for hard
contact lenses, 0.01% in eyedrops

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16
Q

What are some of the alcohol preservatives used?

A

Chlorbutol and phenoxyethanol

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17
Q

What sort of preparations can a preservative be added to?

A

The majority of oral liquid
preparations
* Creams and lotions (not
ointments)
* Most eye drops and eye irrigations
* Injectables that are allowed to be
multi-dose
* Nose and ear drops

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18
Q

What are some of the reasons for not including preservatives?

A

Due to toxicity
Patient sensitivity
Some preparations are intrinsically preserving
If a medicine is unlikely to promote microbial growth or the infection risk is low with things such as powders or capsules.

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19
Q

What preparations do not include a anti-microbial preservative?

A

Single use injections, all IV infusions and
intrathecal injections
* Irrigations (except for preserved eye
irrigations/washes)
* Eye drops in unit dose containers
* Eye and skin ointments (because there is no
aqueous phase)
* Tablets, capsules, powders, granules (because they are dry)

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20
Q

What can the most active antimicrobial preservatives also interact with?

A

Formulation, cause side effects in the patient and the packaging

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21
Q

What are some examples of Parahydoxybenzoates?

A

Alkyl esters (methyl, ethyl, propyl, butyl) of phydroxybenzoic acid

22
Q

What is the required pH range for parahydoxybenzoate activity?

A

From low acid pH up to about 7

23
Q

How are parahydoxybenzoate inactivated?

A

Non-ionic surfactants

24
Q

What are parahydoxybenzoate provide protection aganist?

A

Fungi but not Pseudomonas

25
Q

What sort of preparations are parahydoxybenzoate used in?

A

Can be used e.g. in creams, oral liquids, eye
drops and injectables

26
Q

What form can’t Chlorocresol be used in?

A

Oral preparations or injectables

27
Q

What form can phenols be used in?

A

Injectables (up to 0.5% for insulin)

28
Q

What demographic should alcohol not be in the preparation of drugs for?

A

Neonates due to toxicity

29
Q

What preparation is given in a diazepam injection?

A

Propylene glycol

30
Q

When is Benzalkonium chloride normally used as a preservative?

A

In eye drops (0.01-0.02%) and injectables

31
Q

What is benzalkonium chloride often given in combination with for protection against pseudomonas?

A

Disodium edetate

32
Q

What is the optimal pH for benzalkonium chloride activity?

A

Neutral to slightly alkaline

33
Q

When is chlorhexidine often used?

A

Eye preparations (0.01%)

34
Q

What are some of the advantages of using chloroform as a preservative?

A

Activity over a wide pH range and a broad spectrum of antimicrobial activity.

35
Q

What are some of the disadvantages of using chloroform?

A
  • It is however nephrotoxic and a recognised
    carcinogen; particularly toxic to babies (UK is
    almost unique in still using Chloroform)
  • Has been associated with fatalities –
    dispensing errors
  • It is volatile and is readily lost by evaporation
    during manufacturing and use.
  • A 2 – 4 week “in use” shelf life is applied to
    products preserved with chloroform
36
Q

What do benzoates and sorbates have good activity aganist?

A

Gram positive bacterium and as antifungal

37
Q

How does change in preservative concentration affect the efficacy?

A

Normally varies exponentially. Extent of change depends on the type of agent.

38
Q

How does change in product temperature impact the efficacy?

A

This will alter efficacy in proportions related to different types of preservative and certain groups of microorganisms. Thus, a drop in temperature from 30 to 20°C could result in fivefold and 45fold losses of killing power towards Escherichia coli by phenol (Q10 = 5) or ethanol (Q = 45), respectively

39
Q

What are the other two factors that impact preservative efficacy?

A

Size of inoculum
Preservative capacity

40
Q

In weakly acidic preservatives what form of the molecule are active?

A

The non-ionised form

41
Q

Why are Benzoic and sorbic acids not active above pH 5?

A

Due to their non-ionizable ester group and poorly ionizable hydroxyl
substituent (pKa ca. 8.5) have moderate protective effect even at neutral pH levels.

42
Q

How do preservative molecules distribute themselves in a oil in water emulsion?

A

the oil phase by partition,
* the surfactant micelles by solubilization

43
Q

What equation defines the partitioning of preservative molecules?

A

Conc in aq= Total conc x oil-water ratio +1/ oilwater partition coefficient x oil-water ratio +1

44
Q

What are some examples of preservatives interacting with packaging materials?

A

Phenolic preservatives permeate into rubber closure of eye drops
Quaternary ammonium preservative levels are reduced by adsorption onto plastic and glass containers
Volatile preservatives such as chloroform are
lost by the routine opening and closing of
containers

45
Q

What do you mix parabens to increase activity?

A

Germall 115

46
Q

What is the concept of synergy?

A

Activity of the combined agents is greater than that expected from the agents applied individually

47
Q

How does solubility change by increasing the carbonyl chain length?

A

Aqueous solubility decreases in order: methyl, ethyl, propyl and butyl ester

48
Q

What is the procedure for testing the efficacy of anti-microbial organisms?

A
  1. Prepare a series of containers containing the products and preservative contained within as normally prepared.
  2. Give a incolum of the test organisms either 10^5 or 10^6 per ml or per gram.
  3. The total volume of the added
    suspension of the test organisms must
    not exceed 1% of the volume of the
    product
  4. Mix thoroughly
  5. Remove a sample from each product at time zero and the other specified times.
    6.Use TVC methodology to count
    survivors
49
Q

What are some examples of the test organisms used?

A

Aspergillus niger (Fungal spores)
▪ Candida albicans (Yeast)
▪ Pseudomonas aeruginosa (Gram –ve bacillus)
▪ Stapylococcus aureus (Gram +ve coccus

50
Q

Why is testing the efficacy of preservatives required?

A

Ensure the activity has not been impaired by:
-Storage
-Active constituents within the preparation
-The formulation

51
Q

What is acceptance criteria A?

A

Would have to bring about a 2-log (99%) reduction in viable count of all the challenge bacteria within 48 hours; a 3-log (99.9%)
reduction at 7 days and the count should
remain at that low level for 28 days.

52
Q

What is the acceptance criteria for fungi?

A

Should be reduced by 2-logs at 14 days and be shown not to have increased from that value when tested at 28 days

Infections (16 decks)

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