Pharmacology Flashcards
what is the minimum effective concentration (MEC)?
the concentration a drug must reach in plasma to be effective
what is the maximum tolerated concentration (MTC)?
the concentration of a drug in plasma that will cause unwanted side effects
how is a drugs therapeutic ratio (TR) calculated?
MTC/MEC
do safer drugs have high or low TRs?
high
unsafe = low
what is ED50?
the median effective dose of a drug
what is TD50?
the median toxic dose of a drug
what is LD50?
the median lethal dose of a drug
when does a drug interaction occur?
when the effects of one drug are increased/decreased by the administration of another
describe a pharmacodynamic drug interaction
drug A modifies the effect of drug B, without altering its concentration in tissue fluid
which type of drug interaction is more predictable?
pharmacodynamic
describe a pharmacokinetic drug interaction
drug A modifies the concentration of drug B that reaches its site of action
name a drug that can increase rate of emptying of the stomach
metoclopramide
name a drug that can decrease the rate of emptying of the stomach
atropine
how can antibiotics cause failure of contraception?
enterohepatic recirculation of oral contraceptives may be reduced by antibiotics
what effect does phenytoin have on the efficacy of warfarin?
decreases by inducing enzymes
what effect does cimetidine have on warfarin?
increases efficacy by inhibiting enzymes
what is the result of the drug interaction between simvastatin and grapefruit juice?
myopathy
what is the result of the drug interaction between warfarin and clarithromycin?
enhanced anticoagulation
what is the result of the drug interaction between phenytoin and omeprazole?
phenytoin toxicity
what is the result of the drug interaction between azathioprine and allopurinol?
azathioprine toxicity
what is the result of the drug interaction between catacholamines and MOA inhibitors?
hypertensive crisis
what is the result of the drug interaction between ciclosporin and st johns wort?
loss of immunosuppression
what is the result of the drug interaction between lithium and diuretics?
lithium toxicity
what is the result of the drug interaction between methotrexate and NSAIDs?
methotrexate toxicity
what is the result of the drug interaction between salbutamol and atenalol?
inhibits the bronchodilator effect
what is the result of the drug interaction between benzodiazepines and alcohol?
increased sedation + risk of falls
what is the result of the drug interaction between ACEis and NSAIDs?
increased risk of renal impairment
what is the result of the drug interaction between digoxin and diuretics?
digoxin toxicity
what is the result of the drug interaction between warfarin and aspirin/NSAIDs?
increased risk of bleeding
what effect do competitive inhibitors have on Km and Vmax?
high Km
same Vmax
what effect do non competitive inhibitors have on Km and Vmax?
same Km
low Vmax
what is the extraction ratio (ER) of a drug?
the rate of drug removal from the bloodstream relative to the rate of drug delivery to the liver
what effect does reduced synthesis of plasma proteins due to liver disease have on drugs?
increased toxicity of highly protein bound drugs with low TRs
i.e. phenytoin
what effect does reduced synthesis of clotting factors due to liver disease have on drugs?
enhanced sensitivity to oral anti-coagulants
what effects can drugs have on hepatic encephalopthy?
can be worsened or precipitated
sedatives, opioids
what effect can drugs have on ascites?
may be worsened by drugs that cause fluid retention such as NSAIDs
