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Lecture 1

NEUR 3204 Lecture 1: Lecture 1

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Carleton University
NEUR 3204
Patrice Smith

*Know the definition of bioavailability and what it means. Lecture 1: Principles of Psychopharmacology: From Drugs to Behaviour What is Pharmacology? ➢ Pharmacology is the study of drug action, interactions that occur between a living organism and chemicals that alter normal biological functions. o If behaviour is changed, then it’s Psychopharmacology. o This is the entire physiology, not so specific. ➢ Often confused with pharmacy, a separate discipline in the health sciences that deals with preparing and dispensing medicine. What is Psychopharmacology? ➢ Psychopharmacology is the study of the effects of drugs on the brain and on behaviour (DRUGS & BEHAVIOUR). o If a drug has an impact on the brain, it’s logical to say it will then have an impact on behaviour. ➢ The term drug has many meanings: o Medication to treat a disease. o A chemical that is likely to be abused. ▪ An exogenous chemical that significantly alters the function of certain bodily cells when taken into the body (chemical is generally not required for normal function). o So not only medications, but also anything that can be taken into the body and affect bodily/brain function. Nature’s Drugs ➢ Food and other substances derived from plants and other natural sources can elicit potent drugs effects. o Can be considered psychoactive in nature, an example being tobacco leaves. Specific vs. Nonspecific Drug Effects ➢ Physical and biochemical interactions of drug with target site. o Specific receptors in the brain that facilitate a behaviour as a result from a drug. Some people have more or less receptors, which influences how the drug will affect them. ➢ Based on unique characteristics of the individual. o Susceptibility is different between people. ➢ Pharmacokinetics is the study of drug absorption, distribution within body, and drug elimination. ********* o Absorption depends on the route of administration. ▪ Oral has to go trough the mouth—so you have to design a drug that can pass through an acidic environment. So absorption plays a part. o Drug distribution depends on how soluble the drug molecule is in fat (to pass through membranes) and on the extend to which the drug binds to blood proteins (albumin). ▪ More soluble = more of an effect. ▪ Bioavailability. o Drug elimination is accomplished by excretion into urine and/or by inactivation by enzymes in the liver. ▪ Sometimes, even prior to getting to the site of action, drugs can be degraded in the liver. Has to be taken into account. So dosage is more than necessary, but that’s under the assumption that some will be lost before it can activate the correct receptors. Pharmacokinetic Factors that Determine Bioavailability of Drugs ➢ Bioavailability: A principal pharmacokinetic property of drugs, refers to the portion of drug that reaches blood circulation. Speaks to the amount of drug in the blood stream that can actually get to its receptors. Intravenous, which goes right into the circulation, is much more bioavailable than oral, which has to go through the stomach first. o Route of drug administration. o Absorption and distribution. o Binding to blood proteins. o Inactivation. o Excretion. Routes of Drug Administration ➢ Something in the blood stream still must be able to cross the BBB. Then it’s available to bind to the receptors. ➢ These are good multiple choices: ➢ Intravenous (IV): into a vein (rapid absorption). o Immediately bioavailable. ➢ Intraperitoneal (IP): into the gut (used in lab animals). ➢ Subcutaneous (SC): under the skin. ➢ Intramuscular (IM): into a muscle. ➢ Inhalation of the drug into the lungs. ➢ Topical: absorbed through the skin. ➢ Oral: via the mouth. ➢ How and where the drug is administered will determine how quickly the drug is absorbed and enters the bloodstream. o Bioavailability. ➢ Dose-response (DR) curve: depicts the relation between drug dose and the magnitude of drug effect. o Drugs can have more than one effect. o At the max, all the receptors are being used, so adding more drugs won’t do anything. ➢ Drugs vary in effectiveness (****), depending upon: o Site of action. Receptor could be used up. o Affinity for receptors. Maybe it doesn’t bind super easily. o The effectiveness of a drug is considered relative to its safety (therapeutic index). Maybe it sucks at crossing the BBB. The Time Course of Drug Blood Level Depends on Route of Administration ➢ Oral o Slow and highly variable absorption. o Less predictable blood levels. o Subject to first-pass metabolism. ▪ Metabolism facilitated by liver enzymes which impact how much of the drug gets into the blood stream. ➢ Intravenous o Most rapid form of administration. ➢ Intramuscular o Slower but more even absorption. ➢ Subcutaneous o Slow and steady absorption. ➢ The purple in the bottom of graph is oral, showing it’s slow and unpredictable. Intravenous ➢ Overdose is a distinct possibility and difficult to reverse (by-passes stomach). ➢ Very reinforcing. o Immediate rush from the drug injected. Intramuscular ➢ Rate of absorption depends on rate of blood flow to muscle. o Better circulation in muscle tissue means quicker response. ➢ May cause muscle
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