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Drug Targets (Enzymes (Enzyme Inhibitor: Drug prevents a substrate from…
Drug Targets
Enzymes
Enzyme Inhibitor: Drug prevents a substrate from entering the enzyme's active site so no reaction is catalysed
COX-1 is found in normal physiology, COX-2 is induced when inflammation occurs
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ACE inhibitors inhibit ACE, preventing the conversion of angiotensin I to angiotensin II. This causes reduced vasoconstriction and less aldosterone.
NSAIDs inhibit the enzyme cyclooxygenase (COX) which breaks down arachidonic acid to prostaglandin H2 - prostaglandins stimulate the feeling of pain
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Effectiveness of Drug
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Histamine is an agonist. It causes contraction of the ileum. Mepryamine is an antagonist that reverses the contraction of the ileum
Receptors
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An imbalance of chemicals and receptors can lead to pathology. Example: allergy is caused by increased histamine, Parkinson's is caused by decreased dopamine
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Drug Action
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Efficacy = Describes how well a ligand activates a receptor - only agonists show efficacy. Antagonists have zero efficacy
Tissues have receptor reserves for full agonists, not partial agonists
When a ligand binds to a receptor, it sets off a signalling cascade. This signal can be amplified to give a more powerful response - the type of tissue dictates signal amplification
Allosteric ligand can modulate the effect of an agonist on the receptor. An allosteric modulation is positive, an orthosteric modulation is negative
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Transporters
Antiporters allow a molecule to use the energy from another molecule moving down its concentration gradient to move against its own gradient
Protein pump inhibitors irreversibly inactivate the proton pump in parietal cells, reducing acidity of stomach e.g. Lansoprazole
Symporters use the movement from one molecule to pull in another molecule against their concentration gradient
Diuretics inhibit symporters. E.g. Furosemide inhibits NKCC2 pump on the thick ascending loop of Henle, reducing the amount of ions that can enter the medulla so less water diffuses out of the collecting ducts and more is urinated out. Urination is good for the treatment of hypertension
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Ion Channels
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Calcium channel blockers e.g. amlodipine block the channel, preventing the influx of Ca2+ in muscle so there is less vasoconstriction - treatment for hypertension
Local anaesthetics block voltage gated sodium channels so neurones do not depolarise and no action potential is developed - causes pain relief