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MPharm 2 - PH2107 > Unit 2 - Rectal delivery > Flashcards

Unit 2 - Rectal delivery Flashcards

1
Q

What mass is a suppository?

A

Between 1 g (children) and 4 g (adults)

- depends on the density of the suppository base

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2
Q

What property must a suppository have?

A

Base must melt, soften or dissolve in the mucus secretions of the rectal cavity

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3
Q

What is the drug content of a suppository?

A

< 0.1% - 4%

- generally 1.5 - 2 times oral dose, but can be equivalent

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4
Q

What are suppositories used to treat?

A

Local conditions

  • haemorrhoids
  • fissures
  • fistulas
  • proctitis
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5
Q

Give three examples of soothing agents used in suppositories

A

Mild astringents
Vasoconstrictors
Local anaesthetics

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6
Q

Give examples of mild astringents used in suppositories

A
  • bismuth subgallate
  • zinc oxide
  • hamamelis
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7
Q

Give examples of vasoconstrictors used in suppositories

A
  • adrenaline
  • ephedrine
  • phenylephrine
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8
Q

Give examples of local anaesthetics used in suppositories

A
  • lignocaine
  • benzocaine
  • amethocaine
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9
Q

Give examples of corticosteroids that can be used in suppositories

A
  • hydrocortisone
  • prednisolone
  • betamethasone
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10
Q

Give examples of evacuants that can be used in suppositories

A
  • bisacodyl

- glycerin

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11
Q

Give an example of an antimicrobial that can be used in suppositories

A
  • sulphasalazine
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12
Q

What is an anal polyp caused by?

A

Protrusion of tissue

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13
Q

What is an internal haemorrhoid caused by?

A

Dilated superior haemorrhoidal vein

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14
Q

What is an external haemorrhoid caused by?

A

Dilated inferior haemorrhoidal vein

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15
Q

What is an anal fissure caused by?

A

Tear in mucus membrane

- caused by a change in bowel habits

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16
Q

What is an anal fistula caused by?

A

Abnormal passageway

- caused by infection

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17
Q

What are the advantages of rectal delivery?

A

Can be used to treat systemic conditions where:

  • the patient is debilitated/unconscious/unable to swallow
  • nausea and vomiting present or likely
  • GI disturbance present or likely
  • avoidance of biotransformation in GI tract (pH, enzymes)
  • unacceptable taste
  • partial avoidance of hepatic metabolism
  • avoidance of parenteral route in children (e.g. pre-operative)
  • drugs of abuse
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18
Q

Give some examples of drugs that can be given rectally

A
  • prochlorperazine
  • morphine
  • ergotamine
  • diclofenac
  • indomethacin
  • aspirin
  • paracetamol
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19
Q

What are the disadvantages of rectal delivery

A

UK and USA are averse to using suppositories
- accepted in Eastern Europe and parts of Western Europe
Administration issues
Slow and incomplete absorption
Inter- and intra-subject variation
Formulation

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20
Q

How should a rectal suppository be administered?

A
  1. If necessary, go to the loo to empty your bowels
  2. Wash your hands
  3. Remove any foil or plastic wrapping from the suppository
  4. Either squat, or lie on your side with one leg straight and the other bent
  5. Gently but firmly, push the suppository (tapered end first) into the rectum
    - push far enough that it does not slip out
  6. Close your left and sit still for a few minutes
  7. Avoid emptying the bowels for at least one hour
    - unless the suppository is a laxative!
  8. Wash your hands again
21
Q

Why is it sometimes useful to insert a suppository at night rather than during the day?

A

Once in the rectum the suppository will melt and may leak from the rectum
If you do insert suppositories during the day, be aware that some suppositories can stain your clothes

22
Q

Where should suppositories be stored?

A

In a cool dark place
- not in the fridge unless specifically instructed

If they get too warm, they may melt and not be firm enough to insert

23
Q

What is rectal drug delivery governed by?

A

Physiological and physiochemical factors

24
Q

How long is the rectum?

A

The rectum forms the last 15 to 20 cm of the GI tract

25
Q

How much mucus does the rectum contain when empty?

A

2 to 3 ml (per 300 cm2)

26
Q

How thick is the mucus layer in the rectum?

A

Approximately 100um thick

27
Q

Why are water soluble suppositories painful for the patient?

A

Osmotically attract water to the rectum, increasing the mucus volume

28
Q

Describe the structure of the rectum

A

Non-motile
No villi
Abundant vasculature

29
Q

Why may an evacuant enema be used before administering a suppository?

A

Greater absorption of drug if the colon or rectum is devoid of faecal matter

30
Q

What conditions may affect the absorption of a suppository?

A
  • diarrhoea
  • colonic obstruction (e.g. tumour)
  • tissue dehydration
31
Q

What percentage of drugs in suppositories avoid hepatic first-pass metabolism?

A

50 - 70%

32
Q

Where are drugs in suppositories absorbed into?

A

Rectal / haemorrhoidal veins

33
Q

What is the pH of rectal fluids?

A

pH 7-8

34
Q

What is the consequence of the rectum not having an effective buffering capacity?

A

Drugs will not change chemically and will determine the pH of the environment

35
Q

Which type of drugs are absorbed better in the rectum?

A

Weaker acids and bases are absorbed better than stronger, highly ionised ones

36
Q

What physio-chemical factors affect absorption?

A
  • drug solubility
  • drug particle size
  • base properties
37
Q

How does the solubility of a drug in a suppository affect its absorption?

A
  • lipid/water coefficient
  • lipophilic drugs (especially at low concentration) will be less readily released from a lipophilic base
  • hydrophilic drugs should release readily (especially at high concentration
  • therefore more water soluble salts (e.g. quinine HCl) preferred in certain formulations
  • water soluble bases dissolve in anorectal fluids
  • rate of drug absorption cannot be increased above a certain drug concentration
38
Q

How does the particle size of a drug in a suppository affect the rate of absorption?

A

Decreased size = increased dissolution = increased rate of absorption

39
Q

What properties must the suppository base have?

A
  • must be capable of melting, softening or dissolving
  • must not be irritating (could initiate a bowel movement)
  • compatibility with drug must be ascertained
40
Q

What are the two stages of absorption of drug from a suppository?

A
  • release of drug from vehicle

- transfer across mucosa

41
Q

What is the rate limiting step of absorption of a drug from a suppository?

A

Partitioning of the drug from the melted base

42
Q

How is the drug in a suppository released from the vehicle?

A

By melting at body temperature (lipophilic vehicles) or dissolving/dispersing in mucus (hydrophilic vehicles)

43
Q

What factors affect the release of a drug from a suppository?

A
  • affinity of drug for vehicle
  • solubility of drug in rectal fluids
  • particle size
  • spreading of vehicle
  • interactions between drug and vehicle
44
Q

What factors determine the transfer of a drug in a suppository across the mucosa?

A

Partitioning and diffusion

45
Q

How does a drug in a suppository pass into the mucosa of the rectum?

A

Drug needs to dissolute (slow for poorly soluble drugs) diffuse through mucus layer and then into and through the epithelium of the rectal wall (passive)

46
Q

What factors affect the transfer of a drug in a suppository into the mucosa?

A
  • lipophilicity (pH dependent for weak acids / bases) - buffer solutions can increase absorption
  • site of absorption
47
Q

Give three examples of absorption enhancers that are included in suppositories

A

Surfactants
Salicylate derivatives
EDTA

48
Q

Give examples of surfactants included in suppositories

A
  • cetomacrogols
  • tweens and spans
  • SDS
49
Q

How do surfactants work in suppositories?

A

Lower the surface tension of the vehicle and mucus barrier

  • increase membrane permeability by interacting with phospholipids
  • phenolics can have decreased absorption

MPharm 2 - PH2107 (26 decks)

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