Suppositries

Question 1

Physiological factors
that affect rectal absorption
Colonic content
circulation route

Answer 1

• Colonic content
• The drug molecules will have a greater opportunity to come into contact with the rectal wall when rectum is void.
  Greater contact = greater absorption of drug
• circulation route
• Lower and middle haemorrhoidal veins and the lymphatic circulation assists in absorption and distribution of drug
  Excellent for drugs that are destroyed by the liver

Question 2

Physiological factors
that affect rectal absorption -
pH and lack of buffering capacity of
rectal fluids

Answer 2

pH and lack of buffering capacity of
rectal fluids
- The quantity of fluid available for drug dissolution is very small (approximately 3 ml). Thus the dissolution of slightly
soluble substances is the slowest step in the absorptive process.
- Oily bases – eg theobroma oil readily melts at body temp but fails to release fat soluble drugs readily - Water soluble bases – eg gelatin, PEG tend to dissolve slowly.

Question 3

Physiocochemical factors of drug and
suppository base that influence rectal absorption
Lipid – water solubility

Answer 3

The rate at which a drug is released from a
suppository and absorbed by the rectal mucous membrane is directly related to its solubility in the vehicle or, in other words, to the partition coefficient of the drug between the vehicle and the rectal
liquids.
 When drugs are highly soluble in the vehicle the tendency to leave the vehicle will be small and so the release rate into the rectal fluid will be low.

Question 4

Physiocochemical factors of drug and
suppository base that influence rectal absorption : Particle size

Answer 4

Undissolved drugs – size of drug particle
determines its rate of dissolution and availability for absorption.
Smaller the particle size –> greater the surface area –> more readily the drug dissolves –> greater the chance for rapid absorption.

Question 5

advantages of suppositories over oral forms

Answer 5

• drugs that are destroyed by first pass effect
• drugs that are destroyed by stomach acid and enzymatic activity
• drugs that cause gastric irritation
  -when oral route is not possible

Question 6

disadvantages of suppositories over oral form

Answer 6

• uncomfortable
• variation of absorption
• expulsion of drug due to poor timing of administration
• may cause irritation to mucous membrane by some bases/drugs

Question 7

Physiocochemical factors of drug and
suppository base that influence rectal absorption: nature of base

Answer 7

fatty/oily bases
- theobroma oil
-synthetic triglyceride mixture
water soluble bases
- PEG
- glycerinated gelatin

Question 8

desirable qualities of a suppository base

Answer 8

• Readily melt at body temp or dissolve in the rectal fluid
• Readily release drug
• Stable on storage
• Non absorbent / non-irritant
• Compatible with many drugs
• Easy to mould and to be removed from the mould.
• Easy handing and economy cost