29 Rectal Administration

Question 1

why is rectal administration done

Answer 1

oral route not possivle
local treatment of rectum/colon
rapid system absorption
oral intake is comprimised by disease of upper GIT

Question 2

structure of rectum

Answer 2

hallow organ with single-cell epithelial layer
no villi - lower surface area

Question 3

transport mechanisms

Answer 3

NO active transport
diffusion passive

Question 4

rectal venous drainage

Answer 4

upper rectum - portal vein - liver
lower rectum - systemic circulation - heart

Question 5

what is the aim for rectal venous drainage

Answer 5

keep in the lower rectum to avoid first-pass metabolism

Question 6

major advantages

Answer 6

avoids gastric emptying and food effects, stomach acid degradation
avoidance of first-pass metabolism

Question 7

major diasvantages

Answer 7

poor patient acceptability
small surface area
potential irritation of mucous membranes
low fluid content (dissolution problem)

Question 8

distribution of enemas in the colon

Answer 8

volume determines how far formulation spreads
lower volume = more localsied
higher volumes = more proximal distribution

Question 9

local effects use of suppositories

Answer 9

haemorrhoids - anaesthetics, steroids, astringents
bowel evacuation - glycerol suppositories, bisacodyl

Question 10

systemic use of suppositories

Answer 10

paracetamol
diclogenac
prochlorperazine
bisacodyl

Question 11

what is a suppository

Answer 11

drug + base

Question 12

requirements of suppository base

Answer 12

melts, dissolves at body temp
rapid solidification during manufacture
narrow melting range
non-irritating, non-toxic
sufficient viscosity

Question 13

types of suppository bases

Answer 13

fatty or water-soluble

Question 14

fatty bases

Answer 14

theobroma oil (cocoa butter)
synthetic fatty bases modern - witepsol, dehydag, cotmar

Question 15

challenges for theobroma oil

Answer 15

polymorphism
B form is stable

excessive heating - wrong crystal forms
slow cooling required

Question 16

advantages of modern fatty bases

Answer 16

controlled melting range
more stable vs theobroma oil
better batch consistency

Question 17

water soluble bases

Answer 17

glycerol-gelatin base
polyethylene glycol (PEG)

Question 18

characteristics of glycerol-gelatin base

Answer 18

type A - acid hydrolysis - cationic
type B - alkaline hydrolysis - anionic
hygroscopic
preservatives requried
slowly dissolves - good for prolonged release

Question 19

polyethylene glycol characteristics

Answer 19

dissolves slowly in rectal fluid
may cause osmotic irritation due to minimal rectal water
peroxide formation possible - airtight packaging

Question 20

what properties does a 95:5 ratio have

Answer 20

soft base and immediate release

Question 21

properties of a 75:25 ratio

Answer 21

harder base and sustained release

Question 22

what base would you choose for a fat soluble + water insoluble drug and why

Answer 22

aqueous base
drug needs hydrophilic medium to be released

Question 23

what base would you choose for a water solubledrug and why

Answer 23

fatty base
hydrophilic drug will partition out into rectal fluid

Question 24

when may you need surfactants

Answer 24

when the drug has low solubility in both aqueous and fat

Question 25

callibration procedure

Answer 25

fill mould with pure base only make around 5 suppositories weigh them calculate the average mass per mould cavity

Question 26

densities for drug and base

Answer 26

drug density > base density

Question 27

definition of displacement value

Answer 27

the displacement value of a drug is the number of parts by weight of drug that displaces 1 part by weight of base

Question 28

counselling points for suppositories

Answer 28

fatty base = refregerated PEG-based may require miostening before insertion

Question 29

counselling for suppository administration

Answer 29

inset past the anal sphincter to prevent expulsion lie of side for a few mins after insertion avoid use if rectal bleeding or infection present

Question 30

effect of density on disaplacement

Answer 30

higher dense drug displaces more base

Question 31

what type of base is most likely to cause osmotic irritation

Answer 31

PEG bases