Polymers: Rectal Drug Delivery

Question 1

Why may a drug be delivered via the rectal route rather than another route?

Answer 1

• Oral administration is problematic - problems with GIT, unconcious patients
• Drug is not suitable for oral administration - GI side effects, instability at GIT pH
• Locally-acting drugs - pain or itching from haemorrhoids, local anaesthetic

Question 2

Describe the absorption of drugs from a suppository in the rectum

Answer 2

1. Melting or dissolution of base
2. Release and diffusion of drugs
3. Drug molecules pass through the mucus layer and cell membranes
4. Drug can enter the general circulation directly or by passing through the strongly metabolic liver (portal vein)

Question 3

List 4 factors which affect the absorption of drugs from the rectum

Answer 3

1. Quantity of fluid available is very small - dissolution difficult and slow
2. Properties of rectal mucus - pH =7.5
3. Contents of the rectum - no esterase or peptidase activity so much greater stability of peptide-like drugs
4. Motility of the rectal wall - waves of contractions, pressure from abdominal organs

Question 4

List the 5 dosage forms used for rectal administration

Answer 4

1. Suppositories
2. Tablets
3. Capsules
4. Ointments
5. Enemas

Question 5

List 3 requirements of suppository bases

Answer 5

1. Melt at or just below body temperature
2. Be easily moulded and removed from the mould
3. Be non-toxic and non-irritant

Bases are often fatty e.g. triglycerides

Question 6

List 2 hydrophilic bases used in suppositories

Answer 6

1. Glycerol - gelatin bases
2. Macrogels

Hydrophilic bases are used much less than fatty ones

Question 7

List 2 problems with hydrophilic bases of suppositories

Answer 7

1. Could draw water from the rectal epithelium resulting in its dehydration and pain
2. Many drugs are incompatible with hydrophlic bases

Question 8

List 4 excipients used in suppositories

Answer 8

1. Stiffening agents
2. Suspending agents
3. Emulsifying agents
4. Preservatives

Question 9

Define: Displacement value (DV)

Answer 9

The number of parts of suppository ingredients that displace 1 gram of base

Question 10

How is the total amount of API required calculated for a group of suppositories?

Answer 10

Total amount of API = N x D
N = number of suppositories to be made
D = amount of API per suppository

Question 11

How is the amount of base required calculated?

Answer 11

Amount of base = (N x Y) - (Total amount of API/DV)
Y = weight of 1 suppository without API
N = number of suppositories to be made

Question 12

What is an enema?

Answer 12

Fluid injected into the lower bowel by way of the rectum

Question 13

What are enemas most often used for?

Answer 13

Cleansing enema = relieves constipation or for bowel cleansing before a medical examination/procedure