pharmacology Flashcards
what is bioavailability
fraction of unchanged drug that reaches systemic circulation
how do you calculate oral bioavailability
area under curve for IV drug =X
area under the curve for oral drug = Y
Y/X x100
what is generic substitution
a different formulation of the same drug
considered equivalent to each other, e.g. neurofen VS Tesco ibuprofen
generics must have a bioavailability of 80-125% compared to the reference product
what is a therapeutic substitution
a different drug with the same effect, i.e. assumed therapeutic equivalence
what are the disadvantages of oral route
patient compliance
patient must be able to eat
variation in bioavailability
what ways will an oral drug fail to enter the circulation
destroyed in gut
not absorbed
destroyed by gut wall
destroyed by liver
this can change depending on the patient
what is an excipient
makes the tablet bigger
what are binding agents for
binds the tablet together
what are lubricants for
involved in manufacturing process
what is the advantage of a drug in solution
quicker to absorb
what is the main site of drug absorption
small intestine, due to large surface area and more neutral pH
what routes can drug pass straight into the circulation
buccal/sublingual
rectal mucosa, no first pass metabolism
in which ways can drugs cross cell membranes
diffuse directly through the lipid
transmembrane carrier protein
rarely: diffusion through aqueous pores and pinocytosis
describe ionisation for weak bases
ionised in acidic pH
absorbed in the small intestine
describe ionisation for weak acids
unionised in acidic pH
also absorbed in small intestine due to large surface area
describe uptake of Levodopa
taken up from stomach and small intestine by a transport carrier
DOPA decarboxylase is present in gastric mucosa which breaks it down
what can affect drug absorption in the GI tract
drugs that alter absorption e.g. antacids, laxatives, vasodilators, some antibiotics
intestinal diseases which affect absorption or motility
e.g. crohns or coeliacs
particle size
first pass metabolism
splanchnic blood flow
efflux pumps
diet
how might intramuscular drugs enter the circulation
lipophilic drugs rapdidly
polar drugs by bulk flow
high molecular weight via lymphatics
how do inhalation drugs work
enter via alveolar epithelium or bronchial mucosa
what are the advantages of intranasal drugs
avoids first pass metabolism
ease, convenience and safety
describe some drugs that can be given topically
corticosteroids
antihistamines
local anaesthetics
transdermal patches eg contraception, HRT, GTN, nicotine
what are the key drug factors
lipid solubility, acidic/ basic, charge and size
what are key biological factors
blood flow, surface area, enzymes, compartment ph
what gastrointestinal diseases might affect drug absorption
diabetic gastroparesis
crohns
coeliacs
what are cortiocosteroids used to treat
eczema
