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37 Cards in this Set
- Front
- Back
What does the concentration-response curve look like? |
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What does the log drug concentration-response curve look like? Describe it |
First part of curve is the concentration which the drug does nothing ( threshold conc) Middle part = linear Then reach maximum response |
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What are the three main types of experiment to measure the effect of a drug? |
In vitro (test tube) In vivo (living animal) Ex vivo (in between in vivo and in vitro) |
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How are a drugs effects measured in vitro? |
Drug effects are studies on a piece of tissue dissected from an animal (or human) and kept alive outside the body Includes experiments on cells grown in tissue culture |
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What are some examples of responses that might be measured from in vitro experiment? |
Changes in the tension of muscle Changes in the activity of an enzyme Changes in the secretion of hormone or neurotransmitter |
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How are a drugs effects measured in vivo? |
Drug effects are studied on the living animal Include clinical trials |
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What are some responses that might be measured from an in vivo experiment? |
Change in blood pressure Change in pain threshold Reduction in allergen-induced bronchoconstriction |
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How are a drugs effects measured ex vivo? |
A tissue or organ is removed from an animal that has been treated with a drug, and the effects that drug has had on the organ function are tested in vitro. |
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What may an example be of an ex vivo experiment? |
To see whether long-term treatment with a drug induces liver damage |
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For experiments in vitro, how are drug concentrations expressed? |
Moles per litre i.e Molar (M) We are interested in the number of drug molecules |
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Will a 1 Molar solution of drug X contain the same number of drug molecules as a 1 Molar solution of drug Y? |
Yes. |
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Most clinically useful drugs act at very low concentrations. What kind of concentrations are these? |
1 x 10 -6M to 1 x10-12M |
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What does a typical in vitro set up look like? |
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How may a concentration-response curve be constructed? |
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How may a cumulative concentration response curve be created? What is meant by a cumulative concentration response curve? |
Don't wash drug off after each addition |
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Why would we use the cumulative approach? |
In tissues that respond slowly, so we don't have to wash drug out between times. |
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Why is it not possible to use molar concentrations in vivo? |
Because the volume of solvent (e.g blood) is not known |
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How are drug doses expressed in vivo? What does this allow for? |
As a weight of drug per weight of animal e.g 1mg per kg Approximate extrapolation of the dose from, for example, a 20g mouse to a 70 kg human |
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What is the Emax? |
Indicates the maximum response a drug can produce Increasing the contcentration of the drug produces no greater effect |
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What is the EC 50? |
The Molar concentration of drug that produces 50 % of the maximum response for that drug (sometimes use other percentage values e.g EC90 or EC20) |
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What is meant by potency? A potent drug is effective in small or large amounts? |
Describes the concentration at which a drug is effective (often quantified using the EC 50) Small |
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How can the EC 50 be used to measure the potency of a drug? |
The lower the EC 50, the more potent the drug. |
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Comparing the EC 50 values for two drugs with the same action allows us to calculate what? |
Their relative potencies, describes by the potency ratio (M) |
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Which drug is more potent, A or B? |
Drug A |
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Assuming A to be our standard drug, and B to be the test drug, then what is the potency ratio and how is this calculated? |
M = EC50 (test) / EC50 (standard) 300/15 =20 M=20 |
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How can we calculate Log M? |
Log M = logEC50(test)- logEC50 (standard) |
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What does a potency ratio >1 indicate? |
The test drug is less potent than the standard |
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If we are developing a new drug, what do we want the potency ratio for it to be? |
<1 This indicates it is more potent than the standard |
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What is a bioassay? |
Way of measuring the effects of a drug in a biological system |
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What is a "2 + 2" bioassay? |
The simplest bioassay for determining the relative potency of 2 drugs Take 2 concentrations of the standard, then take 2 concentrations of the test drug and compare them |
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What does the "2 + 2" bioassay make use of? |
The middle portion of the log concentration-response curves are almost linear, and if the two drugs are acting by the same mechanism, then the lines should be parallel. |
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How can 'M' be obtained in a "2 + 2" bioassay? |
Comparing 2 doses of the standard (S1, S2) with 2 does of the unknown (U1, U2) |
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What do the dotted lines represent? |
An average |
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What is meant by the therapeutic index? |
The ratio between the toxic dose of a drug and the dose producing the desired therapeutic effect |
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Do we want the therapeutic index to be high or low? |
High The higher the therapeutic index, the less chance of the drug producing toxic side effects |
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Why is the therapeutic index no longer used? |
We are not interested in the concentration that kills people, more interested in a drug concentration that causes harm Ethically no longer defensible to obtain LD 50 values in animals A drug can have different ED 50's depending on the disease being treated Wide person to person variation in both toxic and beneficial effects of drugs |
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In humans, what is the therapeutic index? |
TD50 /ED50 where TD 50 is the "toxic" does in 50% of the population |