Absorption and Distribution Flashcards
What is absorption?
A mass transfer process of unchanged molecules from the site of absorption into the bloodstream.
Where is the site of absorption usually?
Usually the same as the site of administration but not always the case.
Name some of the factors which may impact the drug reaching the plasma.
-Physiochemical properties of drug (molecular size, shape, how likely it is to ionise in certain environments, its lipophilicity, etc.)
-Dosage form
What is the bioavailability of IV drugs?
100%
In which type of medication do we not want any absorption?
Topical medication
What is the intention of topical medication?
Drug not to make it into the systemic circulation, i.e. for it not to be absorbed.
Why is topical medication useful?
By applying medication directly to the affected part, and ensuring that it isn’t systemically absorbed means that we can avoid “off-target” adverse effects by reducing overall exposure beyond the site of action.
Give an example of a topical medicine.
Creams, eye drops, etc but also local anaesthetics,
How do local anaesthetics bring about their
effect?
Pain signals rely on fast-acting voltage-gated sodium channels
How can local anaesthetics be administrated?
Creams, numbing gels, injections
Why do you not want local anaesthetics to be absorbed?
-If you take the drug away from the site of action, you terminate its effect.
-Fast-acting voltage-gated sodium channels are not confined to the peripheral pain-transmitting nerves.
What are the effects of too much anaesthetic in the CNS?
Agitation, tinnitus, visual disturbance… seizures
->this is because paradoxically excitatory due to blockade of cortical inhibitory pathways
What are the effects of too much anaesthetic in the heart and CVS?
Complex, but eventually bradycardia, hypotension and cardiac arrest (difficult to salvage)
Suggest some steps that will minimise the chances of local anaesthetic getting into the circulation.
-Avoid injecting into circulation.
-Avoid injecting into highly vascular tissues.
-Co-administer the drug w adrenaline as will cause vasocontriction and reduce the chances of the drug being absorbed.
Name two forms of administration you might choose when you want the drug to be absorbed systemically.
-Enteral administration
-Parental administration
->for your info-
enteral=oral; sublingual; rectal
parental=SC, IM ,pulmonary, nasal, IV
What administrative group is the most desirable?
Why?
Oral
->cheapest, no equipment required, easiest, non-invasive
What can solubility be affected by?
Gut contents
Where are most drugs absorbed?
Small intestine as has larger surface area than stomach
What is first class metabolsim?
Any metabolism that happens before the drug gets into the systemic circulation.
What is phase 1 metabolism?
Phase I metabolism involves the additional of a functional group.
What is phase 2 metabolism?
Phase 2 metabolism involves the addition of a conjugation.
What is the first barrier for drugs administrated orally?
Involves surviving those pre-systemic chemical and biological changes.
What is the main barrier to absorption?
Endothelium
Define paracellular movement.
Drugs moving between cells.
