Textbook Notes (362,796)
Canada (158,054)
Psychology (9,545)
PSYC62H3 (273)
Chapter 4


6 Pages
Unlock Document

University of Toronto Scarborough
Zachariah Campbell

CHAPTER 4: PROPERTIES OF DRUGS DO ENVIRONMENT STIMULI CONTRIBUTE TO HEROIN TOLERANCE? • Sheppard Seigel suggested that condition changes may partly account for heroin overdose in experienced users. PHARMACOKINETIC PROPERTIES AND DRUG PASSAGE THROUGH THE BODY • Pharmacology consists of 2 subfields: Pharmacokinetics (how drug moves throughout the body) and Pharmacodynamics (how drug causes biological changes in the body) • Pharmacokinetics properties have a lot to do with how people use drugs • Different methods of intake do not change how drugs act in the brain, but determine how quickly it reaches the brain • Pharmacokinetic issues explain the common administration methods for the drug • The process of pharmacokinetics involves factors concerning how a drug is administered, absorbed into the bloodstream, permeates different body parts, and is eliminated from the body • It is important for drugs to reach the site of action but designing drugs to pass through the body is not easy • There are 4 primary stages of a drug's pharmacokinetic properties: Absorption, Distribution, Metabolism, and Elimination (Figure 4.1) Absorption • Process of absorption refers to the entry of drug into circulatory system • Before entering into the circulatory system, the drug must diffuse through different membranes and into organs. The particular membrane depends largely on drug's route of administration • Route of administration determines how much drug reaches the bloodstream and the length of time need for absorption (Figure 4.2) • Most therapeutic drugs are taken orally in which the drug passes through the stomach and into intestines. Most drug absorption occurs in the small intestine. Orally administered drugs must be encased within a tablet or capsule to protect it from digestive acids in the stomach. At the same time, much of the tablet or capsule must be dissolved by the digestive acids to free drug molecules for absorption. This often reduces the amount of drug that actually reaches the bloodstream • Delay for drug effects depends on the time it takes for the drug to pass through the digestive system and also on the unique chemical properties of the drug and the substance its delivered in. • Most drugs take several minutes to reach bloodstream. 15min to an hour for intestinal absorption. Analgesic (pain-relieving) drug Tylenol takes 30min • Table 4.1 covers other routes of Administration • Inhalation brings the drug directly to the area needing treatment ex. albuterol for asthma. Inhaled substances absorb more quickly than those orally administered. Ex. tobacco takes 7 seconds to reach brain. But, not all inhaled substances reach bloodstream • Intravenous injection involves drug delivery into vein through hypodermic needle. This route of admin involves no absorption limitations, absorption is full and rapid, is preferred by users of abused drugs, and is often used in emergency by physicians or when patient is unresponsive, ex. injection of naloxone to a patient experiencing heroin overdose • Psychiatric medical care staff may deliver drug through intramuscular injection or intranasally by nasal spray (if drug is sublingually deliverable) if patient refuses to swallow antipsychotics Distribution • Distribution refers to passage of a drug through the body which involves passing membranes to reach site of drug action. Psychoactive drugs must pass blood-brain barrier to reach CNS. This phase affects the drug's bioavailability, ability of drug to reach a site of action. • Poor bioavailability ends clinical trial testing to experimental drugs (Figure 4.3) • Drugs used by mothers can permeate the placental barrier, enter placenta, and harm the baby • Nonspecific binding - binding of the drug to sites that are not the intended target for drug effects. This occurs by protein binding (when drug binds to proteins in the bloodstream and as a result, it can't cross the blood-brain barrier) or by depot binding (when drugs bind to receptors or other parts of the body that drug doesn't affect) Metabolism • Metabolism is the process of converting drug into one or more other products called metabolites (product resulting of enzymatic transformation of a drug). It mostly occurs in liver and sometimes in the stomach. Most drugs are broken down by members of CYP-1, CYP-2, and CYP-3 cytochrome P450 enzymes • Enzymes can affect a person's response to drugs. Poor metabolizers are people who either have fewer enzymes needed to metabolize the drug or their gene polymorphisms have a diminished ability to metabolize the drug. These people would have greater treatment sensitivity because the unmetabolized drug will remain in the body longer. And ultrarapid metabolizers either they have more enzymes or greater ability of enzymes to metabolize. They have weaker treatment sensitivity. • Blood testing for these enzymatic activities provides an important approach for personalized medicine, a method of prescribing drugs most appropriate for a patient's unique biological makeup • Sometimes orally administered drugs metabolize before reaching site of action (Figure 4.4). This process is called first-pass metabolism. Ex, 90% of buspirone (BuSpar) converts to metabolites in the stomach before reaching CNS • Metabolites may act in the body, be harmful, or interact with other drugs. Active metabolites can offer pharmacological effects of their own. Ex. enzymes convert quetiapine (seroquel) to metabolite N-desalkylquetiapine, which functions as an antidepressant. Active metabolite that is converted from an inert compound is called a prodrug (biologically active compound converted through metabolism of an inert substance). Lastly, drug tests assess metabolites because they reveal the substance a person used. Elimination • Elimination is the process by which a drug leaves the body. It can occur through urine, feces, sweat, saliva, or breath, depending on the drug. Alcohol is partly eliminated through breath which is why breathalyzers are used to determine alcohol consumption • Drugs have an elimination rate - amount of drug eliminated from body over time. For most drugs, this rate occurs in half-lives. Half-life is the duration of time necessary for the body to eliminate half of a drug, usually based on measuring drug concentration in blood. Drug eliminated in half-lives are referred to as having first- order kinetics. Alcohol and drugs that are not eliminated in set half-lives are referred to as having zero-order kinetics. • Elimination rate varies by dose and drug levels in blood. 10-14ml of 100% alcohol is eliminated per hour. Elimination rates also determine how long a drug's effects will last. Doctors rely on these rates when prescribing how frequently to take a drug, so that the patient takes his next dose when first one starts to subside. In doing so, drug effects reach a steady state (a sustained level of drug in the body) PHARMACODYNAMICS: DESCRIBING THE ACTIONS OF DRUGS • Pharmacodynamics refer to mechanisms of action for a drug. It often deals with actions of a drug at synapses since psychoactive drugs may alter any stage of neurotransmission at synapses, depending on the drug's unique characteristics • Certain substances can interfere with the propagation of action potentials. Ex. Tetrodotoxin is a toxin found in puffer fish which prevent action potential from occuring by blocking sodium channels, which causes cessation in neurotransmission. Puffer fish uses this toxin to paralyze its prey and researchers use it to study brain • Figure 4.7 provides examples of drug actions on dopamine neurotransmission • Many substances alter synthesis for dopamine. L-3,4-dihydroxyphenylalanine or L- DOPA is a precursor for dopamine that is used to treat Parkinson's disease (movement disorder produced by destruction of dopamine neurons in the nigrostriatal pathway). Increasing number of L-DOPA molecules in dopamine neurons increases production of dopamine. As a result, L-DOPA counteracts dopamine loss in Parkinsons. But it does not prevent further dopamine loss and eventually neural loss reaches a point where no medication works. • Drugs like amphetamine interfere with dopamine storage by entering dopamine vesicles and expelling dopamine. Dopamine then leaks out from axon terminal and enter synaptic cleft where it binds to dopamine receptors and increase dopamine neurotransmission • Drugs like antipsychotic haloperidol interferes neurotransmission by binding to dopamine D r2ceptor which prevents dopamine from binding to and activating the D 2eceptor. Haloperidol acts through a basic receptor mechanism called receptor antagonism • Drugs can also alt
More Less

Related notes for PSYC62H3

Log In


Don't have an account?

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.