drug delivery systems Flashcards
(32 cards)
4 types of drug delivery
oral
injection based
transdermal
carrier based
examples of delivery methods (7)
tablets/capsules - regular or modified release; prodrugs; enteric coated solutions/suspensions ointments and creams inhalation injections suppositories pessaries
drug formulation
- allows selective targeting of a tissue site to avoid pre- or systemic metabolism
- allow treatment regime to be tailored to a patient’s needs
4 key factors that determine type of drug delivery system used
dose
frequency of administration
timing of administration
desired speed of onset
choosing a dosage regime (6)
find recommended dose: BNF(c) is there impaired renal/hepatic function consider age and weight consider disease to be treated consider drug toxicity give a starting dose and increase to achieve the desired effect
oral medication and absorption
absorption via GI tract (buccal, sublingual, oral, rectal)
oral delivery systems allow blood levels to be maintained in the therapeutic range for longer periods of time
solutions and suspensions
solutions and suspensions are good for old and young patients with swallowing difficulties
may be given NG/PEG tube
rapidly absorbed
absorption depends on gastric emptying (most rapid from small intestine)
what is a suspension
dispersions of coarse drug particles in a liquid phase
dose can be contained in a small volume
high viscosity can lead to significant over/under dosing especially when measuring with a spoon in children
tablets and capsules
- Most commonly used formulation
- Most are highly stable over wide ranges of temperatures
- Low volume, cheap and easy to produce
Dissolution or tablet break down is the rate limiting step in absorption
advantages of tablets and capsules
convenience
accuracy of dose
reproducibility
drug stability ease of mass production
enteric coated tablets
delays disintegration of the tablet in the stomach allowing it to reach the small intestine
- protects the drug from stomach acid
- protects the stomach from the drug
prolonged release formations
- Important to stay on the same brand to prevent toxicity as different brands have different amounts of drug and different formulation
- The time course for a drug in the body can be prolonged
- This can be done by giving the drug in a form that has a slower but sustained rate of release
This type of preparation contains more of the active drug but releases it more slowly over a prolonged period
they can be oral/parenteral/surgical implants
advantages of prolonged/delayed release formations
• Most disorders required prolonged therapy
• Maintains drug levels within a therapeutic range
• Reduces the need for frequent dosing
• Compliance is improved
Improved nursing and doctor compliance
prodrugs
synthesised inactive derivatives of an active drug which requires to be metabolically activated after administration
advantages of prodrugs
• prolongation of duration of action
avoidance of degradation of the drug in the gut
buccal and sublingual administration
- Ideal method for drugs which have extensive pre-systemic or first pass metabolism
- Sublingual tablets are small and dissolve slowly under the tongue or in the buccal cavity
- Most common example is GTN - absorbed through the buccal mucosa (glyceryl trinate for the treatment of angina)
rectal administration
- Useful in the young or old
- Patients unable to swallow
- Drugs may be administered rectally
• to treat local conditions such as proctitis
• to achieve systemic absorption (indomethacin) - Bypass pre-systemic metabolism
- Administered as a suppository
- Used for chronic epilepsy in children to stop seizures
vaginal administration
- Pessaries
- Creams
- Local disease
injection based drug delivery system
- Provide fast systemic effects bypassing first-pass metabolism
- Drugs can be administered in unconscious or comatose patients e.g. can’t respond or swallow
Drugs having short half-life can be infused continuously
IV administration
- Wouldn’t be used if the oral route was just as effective
- Drugs are given intravenously when:
• a rapid onset of action is required
• careful control of plasma levels is required
• a drug has a short half-life - IV formulations may be given
• Rapidly
• Slowly to prevent toxic effects
• Continuous infusion to ensure accurate control of blood levels especially when a drug has a narrow therapeutic index
IM injection
- An injection of the drug is given into the muscle mass
- The drug may insoluble or formulated in an oil base
- Allows a more sustained duration of action up to months
- Depot Injections contraceptive, neuroleptics
May be painful
subcutaneous injection
- A common route of administration
- Easy to use and bypasses need for venous access
Used for insulin, heparin (prevent clotting) and narcotic analgesics (diamorphine)
can destroy the skin if too much is injected
transdermal drug delivery
- Adhesive patches containing the drug are applied on the skin
- For local effect
- The drug crosses the skin surface by diffusion by percutaneous absorption and goes into systemic circulation - this can cause major problems
Bypasses first-pass hepatic inactivation
percutaneous
- Creams. Ointments and Skin patches
Drugs can be administered to the skin to achieve a local effect i.e. steroids or a systemic effect i.e. HRT or nitroglycerin
