Drug Formulation and design Flashcards
(28 cards)
What is pharmacodynamics?
The study of the actions, effects and interactions of drugs in the body
What is pharmaceutics?
The mode of administration of the drug
What is pharmacokinetics?
How the drug is absorbed, distributed, metabolised and excreted
What is bioavailability?
The rate and extent to which the drug is absorbed
What is biotransformation?
The rate and extent to which the drug is metabolised or degraded
What are the possible rates of administration?
Topical
Oral
Injection
Eye drops
Eye ointments
Ballistic
Iontophoresis
Give some advantages to oral administration
Convenient
Relatively inexpensive and safe
Give some disadvantages to oral administration
Absorption rate is variable
Drug may be inactivated by digestive acids and enzymes
Requires px to take when needed
Give some advantages to intravenous administration
Rapid onset
No barriers to absorption
Give some disadvantages to intravenous administration
Infection risk
Irreversible
What should be considered when choosing the method of administration for a drug?
Where the action is needed - is it on the inside or outside of the body?
How long is the action needed for?
Drug stability - what’s its shelf life?
What happens immediately after an eye drop is instilled?
Blink causes immediate loss of drug
Concentration goes from 50% 1 minute after to 0.1% after 8 minutes
How are eye drops absorbed by the body?
Systemic - drains from the eye via conjunctiva and punctae into the nasolacrimal gland, goes to the stomach and is metabolised.
Ocular - absorbed via the cornea, into the aqueous humour which is drained via the trabecular meshwork
What does trans-corneal diffusion require to work?
A concentration gradient
Where does the drug need to be lipophilic (uncharged) in trans-corneal diffusion?
At the epithelium and endothelium
Where does the drug need to be hydrophilic (charged) in trans-corneal diffusion?
At the stroma
Why can’t fluorescein cross/enter the cornea unless it’s damaged?
Charge is too high at pH 7.4 (tear pH)
What is pKa?
Dissociation constant
the pH at which a drug is 50% charged (concentrations of charged and uncharged forms equal)
Can pKa be changed?
No
pH change can be changed to achieve desired result
What factors can affect eyedrop bioavailability?
Drug formulation and design
Corneal integrity - increased absorption if damaged
Topical anaesthetic administration
Iris pigmentation
Px specific factors
What can affect the stability, irritation and efficacy of the delivery of a drug?
pH
Tonicity
Oxidation
Sterility
Outside what pH range will eyedrops sting?
6.6-7.8
Outside what tonicity range will eyedrops sting?
0.5-2% NaCl
150-650 mOsm
How can drug delivery to the eye be enhanced?
Ointments
Local anaesthetic
Benzalkonium chloride
Multiple drops
Slow delivery inserts (gels, CLs)
