Pharmocology principals Flashcards
what is apparent volume of distribution definition?
The theoretical volume that would be necessary to contain the total amount of an administered drug at the same concentration that it is observed in the blood plasma
what is apparent volume of distribution formula?
Vd (liters)= amount of drug in body (Ab in mg)/ Plasma concentration (Cp in mg/L)
What is the loading dose calculation?
Loading dose = Vd x desired Cp (volume of distribution x drug concentration in plasma)
With protein bound drugs, what is measured when you do drug levels ?
Both the bound and Unbound portions
With protein bound drugs, which part of the drug is active?
The free portion
How does the plasma concentration increase with increased saturable drug doses compared to non saturable protein binding?
Less proportionally when compared to non saturable,, as the bound levels stays constant
Where does most metabolism occur?
the liver
Which notable 5 drugs decrease INR when used with warfarin (according to pharm lecture)?
Carbamazepine, phenytoin, rifampicin, cholestyramine, St john’s Wort.
What is P glycoprotein’s function?
It is an efflux channel in the GIT, which normally functions to reduce absorption of drugs from the GIT
what is the equation for clearance
Clearance (L/min) = (Vd x elimination constant)
Clearance (L/min) = Vd x 0.693/ t1/2
What is the equation for steady state
Cpss = (bioavailability x dose) / dosing interval
How long dose it take to reach steady state
5 x t1/2
Which 5 drugs in the lecture have saturable metabolism and thus zero order kinetics
phenytoin, alcohol, theophyllin, aspirin, perhexilline
What is the definition of a non competitive antagonist
Non competitive antagonist - binds irreversible to the receptor, max effect not achievable with agonist
What is the definition of a competitive antagonist
binds reversibly to receptor, max effect still achievable with higher dose of agonist
What is therapeutic range?
Therapeutic range is the difference between therapeutic effect and adverse effect
What is efficacy determined by?
Determined by E max -( max effect - though usually use E50 ) Defined by curve height
What is potency determined by?
Defined by dose at E max or E50 , Gradient and lateral position of curve
What are the 3 main pharmacokinetic changes in the elderly ?
- Decreased clearance (renal and hepatic function decrease), 2.Decreased Vd ( decreased muscle and water, more fat) 3. Decrease Protein binding (decrease albumin)
What are the pharmacokinetic changes in preggars?
- Clearance increased ( increase CO thus increased hepatic and renal blood flow), 2. Vd increases by 20% 3. Decreased protein binding ( lower measured drug levels, but free levels are unchanged)
what is zero order kinetics
Constant amount of drugs is eliminated per unit time, Independent of total concentration in plasma, May occur when elimination enzymes are saturated Examples – phenytoin and alcohol
What are the inducers of cytochrome p450?
CRAP GPS induce me to madness!!
Carbemazepines, Cyclosporin
Rifampicin
Alcohol (chronic)
Phenytoin
Griseofulvin
Phenobarbitone
Sulphonylureas , St John’s Wort
What are the inhibitors of p450?
VICK’S FACE All Over GQ stops ladies in their tracks.
Valproate
Isoniazid
Cimetidine
Ketoconazole
Sulfonamides
Fluconazole
Alcohol (acute)
Chloramphenicol
Erythromycin (macrolides)
Amiodarone
Omeprazole
Grapefruit juice
Quinidine
What is t1/2 calculation?
t1/2 = Vd*k
cl
( k= 0.7)
