Rectal and Vaginal Flashcards
When is rectal delivery used?
When oral route not available
Targetted drug delivery
Patient unable to swallow
Drug is not suitable for oral adminisatrion due to taste, irritation or unstable at low pH or gastric enzymes
Veins in rectal wall
Lower and middle vein drain directly into systemic circulation
Upper vein is portal so should be avoided to avoid 1st pass metabolism
How much mucus is in the rectum?
3ml over 300cm3
What are physiological factors that affect rectal absorption?
Contents of the rectum
Little buffer capacity
Motility of rectal wall
Penetration enhancer
Rectal drug formulations
Suppositories
Ointments and creams
Enemas
Tablets
Soft gelatine capsules
Disadvantages of rectal delivery?
Drug absorption can be incomplete and unpredicatble
High interpatient variability
Inconvenient
Patient compliance and acceptability can be an issue
Large scale production due to low mp of drug
Advantages of rectal delivery?
Useful in developing countires due to less side effects and less training required compared to IM or IV
Factors in suppository manufacture?
Drug is uniformly distributed in a vehicle or base
Drug should be insolube in base
MP around 37°C
Factors affecting choice of base in rectal delivery?
Bland and inert
Compatible with other ingredients
Melt, dissolve or disperse at or below body temp
Good moulding properties
Readily release active ingredient
Types of base in rectal delivery
Fatty base - theobroma oil
Water soluble - polyethylene glycol
Macrogols
What is sodium salicylate used for in rectal delivery systems?
As an absorption enhancer by interacting with calcium ions in the membrane to ncrease permeability
Factors in formulation of rectal delivery?
Drug solubility - low water content of rectum
Rate of release - can be controlled through choice of base
Drug particle size - agglomeration or precipitation
How to calculate weight of base required?
Total weight of drug = no. of suppositories x mould calibration x drug strength
Weight of base displaced by drug = 1/ displacement value x total weight of drug
Actual weight of base required = (no. of suppositories x mould calibration) - weight of displaced base
What can vaginal delivery be used to deliver?
Thrush
HRT
Spermicidal agents
Advantages of vaginal deliver
Large surface area
Rich blood supply
Ease of administration
Prolonged retention
Easy to administer
Disadvantages of vaginal delivery
Limited to potent molecules
Limited moisture causes local irritation
BV can affect pH, so ionisation affects absorption
Advances in rectal
Dividable stick-shaped suppositories to allow for dose altering
Prolonged drug retention through the use of bioadhesives
