Administering drugs topically Flashcards
why not all drugs administered orally?
site of action best treated topically e.g skin disease
due to their pharmacological, biological and chemical properties
risk of significant systemic side effects
example of why insulin not administered orally? and why?
insulin because its a peptide and if taken orally would be destroyed by gut digestive enzymes
administered topical drugs can have what 2 effects?
systemic or local
example of route administration that has a systemic effect topically
patch, inhalation
example of route administration that has a local effect topically
creams, ocular drops
define local effect
drug applied to a localized area of body surface to minimize systemic side effects
define systemic effect
drug applied to a body surface to provide an alternative and convenient route into blood
why spray (eg. GTN for narrowing artery / drug) under the tongue?
tongue set up to absorb things, loads of blood supply
Some examples when topical route of administration is used locally?
to the skin (eczema), eye (conjunctivitis), nose (hay fever) ,lung (asthma) , rectum (constipation) , vagina (thrush)
Some examples when topical route of administration is used systemically?
to the skin (contraception), mouth mucosal membranes (chest pain)
steroid is a drug that can be formulated in many different ways to target different tissues examples:
eczema is cream, asthma is inhaled powder, nose is nasal spray
stratum corneum
outer layer of epidermis , multiple layered and lipid rich
passage of drug through stratum corneum is dependent on?
whether it is lipophilic (utilises intracellular route- readily across cell walls)
or hydrophilic (utilises the intercellular route- diffusing in fluid filled spaces between cells)
paracellular transport
transfer of substances across an epithelium by passing through the intercellular space between the cells
transcellular transport
substance travels through the cell, passing through membrane
lipophilic drug will use what type of transport
transcellular
hydrophilic drug will use what type of transport
paracellular
ointments can be
non-emulsifying (lipophilic) or water soluble (lipophilic and hydrophilic)
non- emulsifying ointments contain
beeswax and paraffin
disadvantage of water soluble ointment
easily washed off
disadvantage of non-emulsifying ointments
messy and inconvenient
creams can be either
lipophilic (water in oil) or hydrophilic (oil in water)
beeswax in drug formulation
drug product stays on skin (harder to wash off)
hole of skin moist so more likely to absorb the drug
physiological response for when bronchioles not receiving not enough oxygen
diverts blood to parts of the lung that have no air getting to it to the bits of the lug that have air getting to it
key points for drug formulations
target site appropriate
drug properties (is drug stable in particular formulation?)
Acceptability to patient
transdermal application
delivery system that releases drug through a rate controlling membrane into the skin
transdermal application works how?
reservoir of drug time (lipophilic mostly) allows released delivery of reservoir
Topical drug administration
Applying medication directly to a particular place on or in the body
Steroids given orally can cause?
Immune suppression, high blood pressure and diabetes
73 year old with severe chest at the gp practice. He needs GTN treatment. This can be given as a GTN spray or IV. There is no oral route. Why? What route can be used?
No oral route = subject to extensive first pass metabolism in the liver
Substantially higher doses required= side effects
IV (in hospital) or topically ( spray)
- well absorbed across mucosal surface of mouth
Drugs are given locally because we can easily access that area of the body. What does this mean?
Means the drug targets the tissue, without affecting other receptors in the rest of the body-minimising side effects
Drug applied to the skin may diffuse from the stratum corneum to?
Dermis- capillary microcirculation- systemic circulation
How can you increase water content of the stratum corneum? What is the effect of this?
Occlusion (blockage/closing of blood vessel or hollow organ) or hydration
Means increased penetration of both lipophilic and hydrophilic drugs
Routes to treat lung topically
Powder
Aerosol
Nebulised solution
Salbutamol (beta 2 agonist)
Why might inhaling drug be good topically?
Large surface area-rapid local absorption
Ensure high Local concentration
Local side effects
Formulations to consider for topical drugs
Target site
Drug properties-is the active ingredient stable in a particular formulation?
Acceptability to patient
Topical application-systemic effect:
Does this route avoid first pass metabolism?
Yes
Example of topical application with systemic effect
Inhaled anaesthetics
Buccal midazolam
Sublingual GTN tablet
Transdermal nicotine patch
Advantage of transdermal application
Avoids fluctuation in plasma concentration
Easy to administer and acceptable to patients
Can be stopped easily
Prolonged drug action
Disadvantage of transdermal application
Only small enough molecules can penetrate the skin this way
Not applying the patch appropriately will affect the dose
Local side effects
Slow to initiate effect
Advantage of topical drug administration
Alternative route if oral not possible
Targets intended site of action
Reduced risk of systemic side effects
High drug concentration can be achieved
Generally accepted by patients
Disadvantage of topical drug administration
Variable time of onset
Still some systemic absorption of drugs
Local side effect e.g. stinging, may be messy/inconvenient
Rapid clearance may require regular administration
Increasing the water content of the stratum corneum via occlusion (blockage/closing of blood vessel or hollow organ) or hydration will result in?
increased penetration of both lipophilic & hydrophilic drugs
salbutamol acts on what receptor? has what effect?
B2 adrenoceptor agonist
acts on smooth muscle and dilates bronchi
