CHAPTER 6 IN THE SYLLABUS: Principles of Pharmacology
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CHAPTER 6 IN THE SYLLABUS:Principles of Pharmacology
Dr. Robert L. PatrickDepartment of Neuroscience
Brown [email protected]
Biomed 370: January 12, 2005
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PURPOSE OF TODAY’S LECTURE
• To provide a basic introduction to pharmacological principles
• To use these principles to help appreciate the approaches taken in the use of drugs to alter the activity of brain neurotransmitters
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WHAT IS PHARMACOLOGY?
• Pharmacology is the science that deals with the mechanism of action, uses, and adverse effects of drugs
• The word ‘pharmacology’ comes from the Greek word for drug: pharmakon
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DRUGS
• Most common description: A substance used as a medicine for the treatment of disease.
• In a larger context: A substance taken because of its biologically active properties. This would include substances such as caffeine, nicotine, alcohol, cannabis, heroin and cocaine.
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Source of Drugs
• Natural: Plants, fungi, microrganisms• Semi-synthetic (making a chemical
derivative of a natural product)• Synthetic
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Source of Digitalis: Digitalis Purpurea (foxglove)
Source of atropine: Atropa belladonna (deadly nightshade)
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DRUG NAMESUSING ANTIDEPRESSANTS AS
EXAMPLES
• GENERIC: FLUOXETINE• PROPRIETARY: PROZAC
• GENERIC: AMITRIPTYLINE• PROPRIETARY: ELAVIL
• Q: Which are easier to remember?
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How Can Drugs Alter Brain Neurotransmitter Activity?
• By altering some aspect of the Life Cycle of the transmitter:
• Synthesis• Storage• Release• Receptor Interaction• Transmitter Inactivation
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What Are The Common Drug Targets?
• Most common targets are body proteins:
• Receptors: Can alter transmitter signaling• Example: Using risperidone to block dopamine
receptors in schizophrenic patients
• Enzymes: Can alter transmitter synthesis• Example: Using L-DOPA, a substrate for DOPA
decarboxylase, to increase dopamine synthesis in the brains of patients with Parkinson’s Disease
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Drug Targets (con’t)
• Transporters: Can alter transmitter inactivation
• Example: Using fluoxetine (Prozac) to inhibit serotonin reuptake in depressed patients
• Ion Channels: Can alter neuronal excitability
• Example: Using phenytoin to block sodium channels in epileptic patients
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3 Types of Neurotransmitters
• Biogenic Amines: Acetylcholine, Dopamine,Norepinephrine, Epinephrine, Serotonin (can have either excitatory or inhibitory actions)
• Amino Acids: Glutamatic acid (excitatory) GABA and Glycine (inhibitory)
• Peptides: Enkephalins, Endorphins, Substance P (can be either excitatory or inhibitory)
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Drug Action
• The degree of drug action at a target site will, in general, depend upon the drug concentration at that site
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And What Determines Drug Concentration?
• Route of administration• Absorption and distribution• Binding• Inactivation• Excretion
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Entry Into The Brain
• The brain can pose a problem for drug entry, due to the blood-brain barrier
• A drug can gain entry into the brain if:• A. It is lipophilic, and can diffuse across
membranes, or• B. A specific transport system exists that
can carry (transport) the drug across membranes
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Drug Effects
• What does a curve look like when you plot drug effect on the y-axis and dosage administered on the x-axis?
• In words: You generate a dose-response curve!
• In pictures: The shape of the curve depends upon whether you plot dosage or log of the dosage on the x-axis
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Points on the Curve
• The maximal effect is called the efficacy• The amount of drug that produces 50% of
the maximal effect is called the potency• The potency is often expressed as the
ED50
• This means that the lower the ED50 the greater the potency (important point to remember!)
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Agonists and Antagonists• Agonist: An agent producing a cellular effect
(e.g., norepinephrine stimulating the heart or acetylcholine inhibiting the heart)
• Partial Agonist: Does not produce as great an efficacy as a full agonist (e.g., buprenorphine at opiate receptors)
• Antagonist: An agent which blocks the effect of the agonist (e.g., atropine preventing acetylcholine action at the heart)
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THERAPEUTIC INDEX
• Therapeutic Index (TI) = TD50 / ED50
• True or False?: If Drug A has a higher TD50 compared to Drug B, then Drug A must also have a higher therapeutic index.
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