Drug Delivery Systems Flashcards
How can a drug delivery system be formulated?
- to allow selective targeting of a tissue site
- to avoid pre- or systemic metabolism
- to allow a 24 hour action
What determines the drug delivery system we use?
- the dose of the drug to be given
- the frequency of administration
- the timing of administration
What must be considered when choosing a dosage regime?
- recommended dose
- renal function
- hepatic function
- age and weight
- disease
- drug toxicity
- starting dose
What is considered oral medication?
- solutions
- suspensions
- capsules
- tablets
- modified release tablets
How are oral medications absorbed?
via the GI tract
How can oral medication be administered?
- buccal
- sublingual
- oral
- rectal
What are solutions and suspensions useful for?
- young
- old
- patients with swallowing difficulties
How can solutions and suspensions also be given?
Via a naso-gastric or PEG tube
Describe the absorption of solutions/suspensions given via ng/PEG tube.
- absorbed extremely rapidly
- most rapidly from the small intestine
What is absorption of solutions/suspensions dependent on?
Gastric emptying
What is a suspension?
Dispersions of coarse drug particles in a liquid phase which can be contained within a small volume
What are suspensions good for?
drugs which are insoluble unpalatable as they are better tolerated
What do oral delivery systems involve?
Use of various polymers and hydrogel based formulations
What is the rate limiting step in absorption of tablets?
Dissolution or tablet break down
What are the distinct advantages of tablets/capsules?
- convenience
- accuracy of dose
- reproducibility
- drug stability
- ease of mass production
What does enteric coating on a tablet do?
enteric coating delays disintegration of the tablet until it reaches the small intestine
Why are tablets enteric coated?
- protect the drug from stomach acid i.e. omeprazole
- protect the stomach from the drug i.e. aspirin
Why are prolonged/ delayed release formulations useful? (5)
- 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
How can the time course for a drug in the body be prolonged?
- reducing the rate of drug absorption
- giving the drug in a form which has slower, but sustained release
What are oral examples of prolonged/delayed release drugs?
- verapamil
- diltiazem
- isosorbide mononitrate
- lithium
- carbamazepine
What are parenteral preparation examples of prolonged/delayed release drugs?
- IM injections
- flupenthixol
- risperidone
What are surgical implant examples of prolonged/delayed release drugs?
- progesterone contraception
- testosterone
What are prodrugs?
Prodrugs are synthesised inactive derivatives of an active drug which requires to be metabolically activated after administration
What are the advantages of using prodrugs?
- prolongation of duration of action
- avoidance of degradation of the drug in the gut
What is buccal/sublingual administration ideal for?
drugs which have extensive pre-systemic or first pass metabolism
Why might a drug be administered rectally?
- to treat local conditions such as proctitis
- to achieve systemic absorption (indomethacin)
Does administration via the rectal route bypass pre-systemic metabolism?
yes
What can be administered vaginally?
- pessaries
- creams
What does the injection based drug delivery system provide?
fast systemic effects bypassing first-pass metabolism
When are drugs administered IV?
- 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
What do IM injections allow?
a more sustained duration of action
What are subcutaneous injections used for?
- insulin
- heparin
- narcotic analgesics
How does the transdermal drug delivery system work?
- The drug crosses the skin surface by diffusion by percutaneous absorption and goes into systemic circulation
- bypasses first-pass haptic inactivation
What do skin patches allow?
The release of a drug from reservoir into the skin and then into the systemic circulation.
How can inhaled drugs be delivered?
- pressurised aerosol
- breath actuated aerosol
- nebuliser
- dry powder device
What are the advantages of inhalation?
- drug delivered directly to site of action
- rapid effect
- small doses used
- little systemic absorption
- reduced adverse effects
What is the major disadvantage of inhalation?
Patient education is essential
Describe the action of monoclonal antibodies.
mAbs act directly when binding to a cancer specific antigen and induce immunological response to cancer cells
Why have mAbs been modified?
For delivery of a toxin, cytokine or other active drug
What do pre-clinical and clinical liposomal packed drugs exhibit?
reduced toxicities with enhanced efficiency
What does nanotechnology allow in drug delivery systems?
The drug can be targeted to a precise location which would make the drug much more effective and reduce the chance of possible side-effects
Name 3 nanocarriers?
- nanoparticles
- nantubule
- nanoshell
What are the advantages of nanoparticle based drug delivery?
- more specific targeting and delivery
- reduction in toxicity while maintaining therapeutic efficiency
What are nanoerythrosomes?
- Resealed erythrocytes that can carry proteins, enzymes and macromolecules
- Used in the treatment of liver tumour, parasitic disease and enzyme disease
What is genetic transfer system in clinical trials for?
- adenovirus
- HIV
