# Lecture 8.docx - PHARMACODYNAMICS what the drug does to...

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PHARMACODYNAMICS: what the drug does to your body; concerned with the mechanisms of action that give rise to the biological and physiological effects of a compound DOSE-RESPONSE CURVE - for every drug, there is a mathematical relationship between the dose and the effect o The dose determines: Whether there is an effect (minimal threshold) The intensity of the effect (up to a point) The effects that are experienced Low-dose effects typically different from high-dose effects Side effects may appear only above certain dose thresholds - Most drugs have more than one effect, but, only one effect is represented in each dose-response curve o Separate dose-response curves for every effect of the drug Primary and side effects, lethality o Dose-response relationship/curve It is common in science to see graphs with dose on x axis and some response on y axis Also called dose-effect relationship Never simply linear; usually bell shaped, bimodal, etc. PHARMACODYNAMICS - Efficacy vs potency - Efficacy is whether or not an effect has been achieved [see image] - The dose-response curve for Tylenol with severe pain relief, the curve would be a flat horizontal line because as you increase dose, the pain relief will not increase - Potency is the minimum amount needed for a drug to yield its efficacy (to have its effect) Nexium has an overall greater efficacy than tums because it has high efficacy for high and moderate acid reflux while tums has high efficacy only for moderate and low (no matter how much you take it will not relieve high reflux). The curves may be different heights but the same shape. However, both drugs can relieve moderate reflux so we can compare potencies. Since it takes less Nexium than tums to achieve moderate relief for both, Nexium is more potent. - When comparing potency of different drugs for the same effect, use a response value that all drugs reach - Most anxiolytic drugs are prescribed in really small doses because they are potent o Taking more results in negative side effects (sedation hypnosis coma) [see image – terminology like EC50; refers to the graphs/curves] THERAPEUTIC WINDOW - Wide therapeutic window – wide range of doses that could work to achieve therapeutic effect and not as likely to kill you o Less overlap between curves: as you increase dose, the chances of you dying aren’t as great until you hit a really high dose

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- Small therapeutic window – more overlap between curves; as you increase dose, the lethality odds are increasing more greatly - We are more concerned with margin of safety: the space between ED99 (99% of patients experience the therapeutic effect) and LD01 (1% experience lethality) - NEUROTRANSMITTER PERSPECTIVE (neurotransmitter “dose”) o Taking a direct agonist will shift the dose-response curve to the left. If you have x amount of neurotransmitter required on the x axis and % response on the Y axis, then taking an agonist for the receptors of the neurotransmitter will shift to the left o

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