How drugs act P2 L14 Flashcards
pharmacokinetics=
factors that determine the active concentration of the drug at the active site
absorption=
the mechanism of accumulation of a drug in a body compartment following administration
distribution=
the way in which a drug reaches each organ of the body
metabolism=
the chemical alteration of a drug into its inactive form
excretion=
removal of a drug and/or its metabolites from the body
what factors determine the conc of a drug at its active site
ADME absorption distribution metabolism excretion
when would a drug be ionised
when pH is opposite to pKa
what drugs can’t dissolve through the lipid membrane
ionised acid and bases
what plasma protein do drugs bind to (especially warfarin)
albumin
what is a bound drug
inactive
what determines distribution of free drugs
lipophilicity
Volume of distribution (Vd)=
theoretical volume that the total amount of drug would have to occupy (if uniformly distributed) to provide the same concentration as is currently in blood plasma
when is Vd low
if drug restricted to plasma water (ionised)-7000mls
when is Vd equal to body volume
if lipophillic - 70,000
when is Vd high
if protein bound 350,000mls
where is the principal site for drug metabolism
the liver
what is a prodrug
an inactive or weakly active substance that has active metabolites
where does the liver filter blood directly from
the small intestine
whats it called when the liver first filters blood from the small intestine
first pass effect
what happens in phase 1 metabolism
drug is made more polar by oxidation, hydroxylation, deamination, hydrolysis
what haem protein does first phase effect involve
cytochrome P450
what do cytochromes do (2)
Induction (decreased drug activity)
Inhibition (increases the activity of a drug)
what happens in phase 2 metabolism
conjugation
examples of substances use to conjugate drugs (2)
sulphuric acid
Glucuronic acid
what is conjugation
combining the drug with another chemical
what does conjugation achieve
makes it more polar and less reactive —> easily secreted
where are drugs excreted (3)
Urine
faeces
lungs
what 2 factors affect drug absorption
pH
lipophilicity
elimination half life=
time taken for Cmax to fall by 50%
Cmax=
maximum plasma concentration following a given dose
Tmax=
time taken between drug dose and achieving Cmax
