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Pharmaceutics > Rectal Route > Flashcards

Rectal Route Flashcards

1
Q

What action can rectal route be used for?

A

Local + systemic

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2
Q

What can rectal route be used locally for?

A

Pain + itch

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3
Q

What can be given to locally treat rectum?

A

Antiseptics, local anaesthetics + anti-inflammatory

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4
Q

Can all drugs given for oral administration be given via the rectal route?

A

YES

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5
Q

What can given to treat systemically?

Rectum

A

Anti-inflammatories, analgesics + anti-asthmatics

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6
Q

How is the drug rectally absorbed?

A

Passive diffusion

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7
Q

What is the rate + extent of rectal absorption compared to oral + why?

A

Lower = small SA

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8
Q

Describe what happens after absorption in rectum

A

Drug enters haemorrhoidal vein, after absorption
Blood in lower + middle haemorrhoidal veins drain systemic circulatory directly
Blood from upper vein enters portal vein, which flows into liver = 1st-pass metabolism

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9
Q

What physiological factors affect rectal absorption?

A

Quantity of rectal fluid
Properties of rectal fluid
Contents of rectum
Motility of rectal wall

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10
Q

Why does quality of rectal fluid affect absorption?

A

Limited fluid in a thin layer

= dissolution poorly for H2O-soluble drugs = rate limiting step in absorption process

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11
Q

Why does properties of rectal fluid affect absorption?

A

Neutral pH, minimal buffering capacity = inability to control degree of drug ionisation
= salt form used to control ionisation to provide local/systemic absorption

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12
Q

What does it mean if there is no esterase or peptidases in rectal fluid?

A

Greater stability of peptide-like drugs

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13
Q

Why does content of the rectum affect absorption?

A

Presence of faeces affects dissolution = effects absorption

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14
Q

What are the rectal advantages?

A

Possible to remove dose
Suitable for drugs liable to degrade in GI tract
Suitable for elderly, terminally ill, paediatric or unable to swallow
Immediate-release or modified-release

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15
Q

What does the rectal route also surpass?

A

1st-pass metabolism

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16
Q

What are the rectal disadvantages?

A 
Compliance poor
Upward movement of dosage
Specialist required
Drug absorption slower than oral
Local side effects
Manufacture of suppositories more difficult
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17
Q

Why is upward movement of dose a rectal disadvantage?

A

Increases 1st-pass metabolism

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18
Q

What are the rectal dosage forms?

A 
Suppositories = most common
Foams
Solutions
Suspension
Emulsions
Rectal capsules
Tampons
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19
Q

Describe suppositories

A

Single dose preparations
Formulated in different size + shapes
Tapered at one end
Excipients may be added

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20
Q

Why are suppositories tapered at one end?

A

Aid insertion

= wider in middle (aid retention)

21
Q

What is the drug content of suppositories?

A

0.1% w/w to 40% w/w

22
Q

Describe the drug-release mechanism

A

Melting or spreading
Sedimentation
Wetting
Dissolution

23
Q

What should the suppository base be?

A 
Solid at RT
BUT soften at 37 degrees 
Non-irritant to rectal mucosa
Physically + chemically stable over shelf-life
Compatible with drug
High viscosity
24
Q

Why must the suppository base have a high viscosity?

A

To minimise leakage

25
Q

What are the 2 types of suppository base?

A

Glyceride - fatty bases

H2O-soluble bases

26
Q

What is an example of a glyceride suppository base?

A

Witepsol

27
Q

What is an example of a H2O-soluble suppository base?

A

Glycerol-gelatin

28
Q

Describe fatty suppository bases

A

Semi or fully synthetic fatty acids

Mixed triglycerides with C12-C18 saturated fatty acid

29
Q

What is the typical melting range for fatty suppository base?

A

33-37 degrees

30
Q

Describe glycerol-gelatin hydrophilic suppository base

A

Mix of gelatin, glycerol + H2O
Higher gelatin proportion
Hygroscopic

31
Q

Why is there a higher gelatin content in glycerol-gelatin hydrophilic suppository base?

A

More rigid + longer-acting

32
Q

Describe polyethylene glycol suppository base

A

Mix of different molecular weight of polyethylene glycols

PEG above 4000

33
Q

What are lower molecular weights of polyethylene glycol?

A

Liquids

34
Q

Why do polyethylene glycol suppository bases have a PEG of above 4000?

A

Waxy solids

35
Q

What are the issues with hydrophilic suppository bases?

A

Small amount of liquid already in rectum = base could withdraw H2O from rectal epithelium
= dehydration + pain
Many drugs incompatible
Drug release slow

36
Q

What excipients may be used?

A

Surface-active agents
Hygroscopicity reducing agents
Melting point controlling agents
Other excipients

37
Q

Why are surface-active agents used?

A

To enhance wetting properties of base with rectal fluid = enhance drug release

38
Q

What is an example of surface-active agent?

A

Sorbitan esters

39
Q

What are surface-active agents added to?

A

Fatty base or lipophilic drug

40
Q

Why are hygroscopicity reducing agents used?

A

Added in fatty bases to reduce uptake of H2O from atmosphere storage

41
Q

What is an example of a hygroscopicity reducing agents?

A

Colloidal silicon dioxide

42
Q

Why are melting point controlling agents used?

A

To increase or decrease melting point of fatty base

43
Q

What are examples of melting point controlling agents?

A

Beeswax = increase melting point

Glyceryl monostearate = decrease melting point

44
Q

What other excipients are used?

A 
Diluents
Adsorbents
Lubricants
Preservatives
Colouring
45
Q

What drugs are normally unsuitable for rectal route + why?

A

Hydrophilic compounds = limited H2O in rectum

46
Q

What does drug solubility in rectal fluid determine?

A

Rate + extent of absorption

47
Q

What happens when a drug has a high base-to-H2O partition coefficient?

A

Likely to be in solution

= lower tendency to leave dosage form

48
Q

What would be the 1st choice of drug for rectal route?

A

H2O-soluble drug dispersed in fatty base

Pharmaceutics (21 decks)

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