Rectal/Vaginal Routes Flashcards
When is rectal delivery used? (2)
for local action e.g. pain and itch
for systemic action
Features of the rectum: (2)
one cell layer thick epithelium
good blood circulation
Drug absorption is by…
Rate of absorption is —— than the oral route?
passive diffusion
lower than than the oral due to small surface area
Following absorption, drug enters the…
haemorrhoidal veins
Advantages of rectal route (3)
suitable for drugs liable to degrade in the GIT or first pass metabolism
suitable for elderly, terminally ill who are unable to swallow oral dosages
possible to remove dosage form to discontinue treatment
Disadvantages of rectal route (3)
poor acceptability and compliance in certain countries
local slide effects
upward movement of the dosage form can increase first pass metabolism
Physiological factors that affect rectal absorption: (4)
contents of the rectum
- presence of faeces affects drug dissolution in rectal fluids
motility of the rectal wall
- the activity of the muscles influences the rate of dissolution
quantity of rectal fluid
- limited fluid, makes dissolution the rate limiting step
properties of rectal mucus
- neutral pH leads to inability to control drug ionisation
Suppositories…
single dose
tapered at one end to aid insertion
diff shapes and sizes - smaller for children
Two types of suppository base:
Glyceride-type fatty bases
witepsol
– Water soluble bases
less commonly used
Problems with the hydrophilic bases: (2)
small amount of liquid in rectum, it could draw water from rectal epithelium resulting in dehydration and irritation
many drugs are incompatible with hydrophilic bases
Excipients include..
melting point controlling agents e.g. beeswax
surface active agents to enhance the wetting properties of the base with the rectal fluid
Vaginal wall is highly…
vascular with a relatively large surface area.
Physiological factors influence absorption in vagina:
thevolume, viscosity and pH of vaginal fluid, the stage of menstrual cycle, age, and sexual activity.
as well as drug related factors
Advantages of vaginal administration (3)
local effects
systemic absorption high due to surface area
suitable where oral intake is restricted
Disadvantages of vaginal administration (3)
gender specific
acidic pH of vagina may enhance degradation of some drugs
menstruation cycle and hormonal variations affect systemic absorption
Ideal vaginal dosage form: (3)
colourless, odourless
free from local irritation
long acting, easy to apply
Semi-solid vaginal formulations
creams, ointments and gels
similar formulation to topical semi-solid formulations
Semi-solid vaginal formulations disadvantages: (3)
applicators tend to be messy and add to product cost
large scale production is challenging
no accurate dose
Vaginal suppositories (pessaries)
similar to the rectal ones
often use glycerol-gelatine as the base
Vaginal rings (implants)
rings are flexible, circular system containing the drug entrapped in a polymer network
controlled release of drug over a period of time
Vaginal tablets
They are solid ,single-dose preparations ,similar to oral tablets in terms of formulation and manufacture
disintegrate in the small volume of vaginal fluid to allow drug release
Two major mechanisms:
- melting
designed to melt at body temp releasing the drug - disintegration
solid dosage forms release drugs by dissolution or disintegration, followed by dispersion of the contents in the vaginal fluids
Manufacture of rectal and vaginal suppositories
using a moulding method.
• The base is heated to above the melting temperature, the drug dispersed or dissolved in the heated liquid.
•The molten product is poured into moulds, cooled then removed for final packing.
Or directly injected into the final packaging (mould strips) then sealed.
