S2.2 Pharmacodynamics Flashcards
What is pharmacodynamics?
What the drug does to the body
Define intrinsic efficacy
Ability of a drug to activate a receptor
Define efficacy
Ability of a drug to produce a response
Define potency
Dose required to produce the desired biological response.
What is Emax and EC50?
Emax - Max response we can measure
EC50 – conc of drug which causes 50% max response
What is bmax and Kd?
Bmax – max binding capacity
Kd – conc of drug which gives 50% occupancy of available receptors
What is the action of antagonists?
Competitive antagonists compete with the agonists, non-comp antagonists bind to the allosteric site which reduces the effects of an agonist.
What is IC50?
Concentration of antagonist giving 50% inhibition.
Define affinity?
Tendency of a drug to bind to a specific receptor type.
Give some examples of CYP450 inducers and inhibitors
CP450 inducers: phenytoin, carbamazepine, rifampicin
CP450 inhibitors: omeprazole, sodium valproate, isoniazid, grapefruit juice
What is the effect of renal disease on pharmacodynamics?
Low GFR so reduced clearance of renally excreted drugs: Digoxin
What is the effect of hepatic disease on pharmacodynamics?
Reduced clearance of hepatic metabolised drugs, Reduced CYP450 Activity, Much longer half-lives. Examples – opiates in cirrhosis
What is the effect of cardiac disease on pharmacodynamics?
Falling cardiac output leads to excessive response to hypotensive agents and reduced organ perfusion
