Routes of Administration (Rectal and Vaginal) Flashcards
Why is the rectal drug delivery used for local and systemic action?
- Local: treatment of pain and itch (drugs include antiseptics, local anaesthetics, anti inflammatory)
- Systemic: Drug should be absorbed through mucous membranes of the rectum (anti inflammatories, analgesics)
What is the rectum anatomy?
- Is part of the colon , forming the last 15-22cm of the GI tract
- Separated from the external by the anus
- Mucus has no enzymatic activity or buffering capacity. Good blood circulation
What are the advantages of the rectal route?
- Absorption bypasses portal circulation through the liver and avoids first pass metabolism
- Patient is unable to swallow, drug is inactivated in stomach acid, drug may cause irritation to the gastric mucosa
What are the disadvantages of the rectal route?
- Patient acceptability and compliance is low
- Upward movement can increase first pass metabolism
- Drug absorption is slowest
- Local side effects
How does the rectal route of drug absorption work?
- Primarily by passive diffusion
- Following absorption, drug enters haemorrhoidal veins
- Blood in the inferior and middle haemorrhoidal veins drain into the systemic circulation directly
- Blood from superior haemorrhoidal vein enters into the portal vein and flows into the liver = first pass metabolism
What are the physiological factors that affect rectal absorption?
- Quantity of rectal fluid
- Properties of rectal mucus
- Contents of the rectum
- Motility of the rectal wall
How does the quantity of rectal fluid affect rectal absorption?
- Limited amount of fluid spreads in a thin layer.
- Dissolution for poorly water soluble drugs can be the rate limiting step
How does the properties of rectal mucus affect rectal absorption?
- pH 7-8 with minimal buffering capacity leads to inability to control the degree of drug ionisation
- Salt form of the drug is used to effectively control ionisation to provide local or systemic absorption
How does the contents of the rectum and the motility of the rectal wall affect systemic absorption?
- Drug will have greater opportunity to be absorbed when the rectum is empty. So enema is given before administration
- Wall muscle activity can influence the rate of dissolution within the rectum
What are factors that influence rectal drug delivery? (may need to change how it is delivered)
- Drug associated (Partition co efficient, solubility, degree of ionisation, particle size)
- Formulation associated (liquid/ solid)
- Pathology associated (bowel disease, hemorrhoids)
- Physiology associated (rectal mucus, motility)
What are the different rectal dosage forms?
- Suppositories
- Foams
- Solutions
- Suspensions
- Emulsions
What are the different rectal semi solids and what are they normally used for?
- Rectal creams, gels, ointments. Packaged with plastic tips
- Topical application to the perianal area
- Treat local conditions of anorectal pruritis, inflammation and the pain associated with haemorrhoid
-Drugs include: Astringents, local anaesthetics
What are supossitories?
- Single dose
- Cone shaped forms with fatty bases (slow melting) or water soluble bases (dissolving)
- Lipophilic drugs use water soluble bases
- Hydrophilic drugs use fatty bases
What are the main stages of the drug release mechanism of suppositories?
- Melting
- Spreading
- Sedimentation
- Wetting (wetting agents reduce surface tension and allows it to spread on surface)
- Dissolution
What are the different types of suppository bases?
- Fatty Base
- Hydrophilic Bases: could draw water from rectal epithelium (dehydration)
- It must be solid at room temp, non-irritant, stable
