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Flashcards in Pharma Deck (202)
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1

Give 3 reasons why someone may make a prescribing errors

-Loss of attention due to exhaustion
-Inappropriate training
-Illiterate hand writing

2

Define pharmacokinetics

-Study of the movement of a drug into and out of the body ie what the body does to the drug

3

Define pharmacodynamics

-Study of the drug effect and mechanism of action oe what the drug does to the body

4

Define pharmacogenetics. Give an example

-The effect of genetic variability on the pharmacokinetics or pharmacodynamics of a drug on an individual
-CYP450 enzymes have genetic variation within the population eg 2D6 and thus some people will not react or over react to a drug which is metabolised by this enzyme eg codeine

5

Give some factors which may effect the pharacokinetics of a drug

-Obesity
-Alcohol consumption
-Other medications
-Liver and renal function
-Albumin concentration

6

What is bioavailability of a drug? How do you calclulate it? Give some factors which affect bioavailability

-The fraction of a dose which finds its way into the circulation unchanged
-[AUC Oral] plasma/[AUC IV]plasma
-Route of administration, age, lipid solubility of drug, absorption of drug, first pass metabolism

7

What is first pass metabolism?

-The metabolism of a drug which occurs before it reaches the systemic circulation. Includes metabolism in the gut lumen by gastric acid/enzymes, gut wall by absorption and the liver

8

Broadly describe the 2 phases of drug metabolism in the liver

-Can either enter phase I or go straight into phase II
-Phase I involves cyp 450 and is a oxidation or reduction reaction which usually inactivaes the drug
-Phase II is a conjugation reaction with glucaronide, glutathione, sulphate which makes the drug water soluble so it can be eliminated

9

What are the two key factors which affect drug distribution and how do they do this?

-Protein binding -> Unbound drugs are able to bind to receptors and pass across cell membranes and have a pharmacological affect. Bound drugs remain in the circulation, therefore if a drug is highly bound the distribution will be less
-Volume of distribution -> a hypothetical measure of instantaneous distribution of drugs into available body compartments. If there is a low volume of distribution it means that the drug will be at high concentration in the body compartments which it can dissolve in

10

If there was a change in protein binding eg drug interactions, what properties of certain drugs would make you concerned?

-If a drug is highly bound -> displacement would rapidly increase the concentration of active drug
-If there was a low volume of distribution -> means the drug is in high conc in the places it is. displacing the drug from protein binding would raise the concentration more
-If the drug had a narrow therapeutic window because displacement could push the drug to toxic levels

11

Give 3 things which may affect protein binding

-Hypoalbuminaemia
-Pregnancy
-renal failure
-Displacement by other drugs

12

What factors have an effect on volume of distribution?

-Lipid solubility
-Regional blood flow
-Specific receptor sites in tissues
-Active transport
-Drug interactions

13

What is a pro-drug?

-A drug which is inactive when administered and becomes activated by the body eg codeine to morphine

14

Name some CYP inhibitors. What affect do inhibitors have on metabolism?

-Grapefruit juice (simvastatin)
-Omeprazole
-Anti-fungals
-Disulfram
-Erythromycin
-Valproate
-Isoniazid
-Cimetidine/Ciprofloxin
-Ethanol (acute)
-Sulphonamides
-Decrease metabolism of drugs prolonging the effects

15

Name some CYP inducers. What affect do inducers have on metabolism?

-Phenytoin
-Carbamazepine
-Cranberry Juice (warfarin)
-Rifampicin
-Alcohol (chronic)
-Barbituates
-St Johns Wort/Sulphonylureas
-Induce the production of the enzymes to increase metabolism of drugs and thus decrease their effects

16

What 3 processes determine the renal excretion of drugs? What is the relationship between clearance and half life?

-Glomerular filtration
-Passive tubular resorption
-Active secretion
-The lower the clearance (GFR) the longer the half life

17

What is first order and zero order kinetics? Why do most drugs exhibit zero order kinetics at high doses?

-1st order = rate of elimination is proportional to drug level and a constant fraction is eliminated -> half life can be calculated
-Zero order= rate of elimination is constant regardless of drug level. half life not easily calculated
-Enzymes and receptors become saturated

18

Why does digoxin need a loading dose? Why does renal failure affect its toxicity?

-It has a long half life and steady state would take 3-5 half lives and you need rapid affect
-In renal failure there is less excretion of digoxin meaning that the drug will remain at toxic levels for longer and the same dose may reach toxic levels as that in a normal kidney

19

Describe the metabolism of paracetamol at therapeutic and toxic doses
What is the treatment for paracetamol overdose?

-Therapeutic -> 90% Paracetamol enters phase II metabolism and excreted, 10% enters phase II and converted to NAPQI but quickly undergoes conjugation with glutathione and inactivated
-Toxic -> Phase II saturated so much higher conc enters phase I metabolism. Produced large amounts of NAPQI and not enough glutathione to reduce so oxidative damage to the liver
-Activated charcoal within 1 hour
-N-acetylcysteine

20

How do competitive antagonist change the dose response curve? How is this over come?

-Keeps the same shape but shifts it to the right
-Adding more agonist (its surmountable)

20

How do non-competitive antagonist change the dose response curve? How is this over come?

-You get the same shape but the total response is decreased
-It cannot as it alters the conformational shape of target

21

What is the difference between drug selectivity and drug specificity?

-Selectivity refers to how well a drug binds to one group of receptor targets without binding to other targets and producing undesirable effect
-Specificity refers to how well the drug binds to a receptor subtype allowing it to be organ specific

22

What is affinity? What pharmacological term is used to measure affinity and how is it interpreted?

-A measure of the tendancy of a ligand to bind to its target
-Kd -> The lower the Kd the higher the affinity

23

What is efficacy? What is potency?

-The abolity of a drug to be able to activate the receptor and produce a response once it is bound
-Potency is how much of the drug is needed to generate a response taking into account affinity and efficacy

24

What is the therapeutic window? How is it calculated?
Give 3 drugs with a narrow therapeutic window

-The range of doses which can effectively treat a condition whilst still remaining safe. It is between the lowest concentrations which cause the desired affect and lowest concentrations causing adverse effects
-EC50-> TD50
-Warfarin, digoxin and gentamicin

25

How can drug interactions be caused during the absorption of a drug?

-Something may prevent the drug being absorbed due to inducible/inhibitable active transporters in the gut

26

Name some drugs which prolong the QT interval

-Cocaine
-Haloperidol
-Erythromycin
-Amiodarone
-Tricyclic antidepressants

27

How can renal disease affect the pharmacodynamics/kinetics of drugs?

-Decreased clearance
-Disturbances in electrolytes may predispose to toxicity eg digoxin and hypokalaemia
-Nephrotoxins will further damage the kidney

28

How can hepatic disease affect the pharmacodynamics/kinetics of drugs?

-Decreased albumin production affects protein binding
-Decreased CYP450 production will change metabolism of drugs
-Reduced hepatic clearance of drugs

29

How can cardiac disease affect the pharmacodynamics/kinetics of drugs?

-Excessive response to hypotensive agents
-Reduced organ perfusion may lead to reduced hepatic flow and clearance and reduced renal flow and clearance