BioPsych Chapter 5

Endogenous

“From within”; substances naturally produced by the body

Exogenous

“From outside”; substances introduced from outside the body

Site of action

Where a drug interacts with the body (e.g. receptors transporters and enzymes)

Mechanism of action

How a drug exerts its effects (e.g. receptor agonism enzyme antagonism reuptake inhibition)

General (systemic) dose

Dose that circulates through the whole body

Local dose

Targets a specific area to treat one issue

Drug

Any exogenous substance that causes a pharmacological effect at a site of action in the body

Chemical name

Describes chemical structure; helps predict function and interactions

Generic name

The drug’s scientific name before being patented; commonly used in medicine and research

Proprietary (brand) name

The patented marketed name of a drug (e.g. Xanax OxyContin)

Street name

Culturally influenced names often used to disguise drugs (e.g. X xannies bars)

Pharmacokinetics

The study of absorption distribution metabolism and excretion (ADME) of drugs

Pharmacodynamics

The study of how drugs interact with the body to produce effects

1st Rule of Pharmacology

The dose is critical—determines toxicity and efficacy

Dose-response curve (DRC)

Graph showing how a drug’s effects change with different doses

ED50

Median effective dose; dose at which 50% show desired effect

LD50 (TD50)

Median lethal dose; dose at which 50% die from the drug

Therapeutic Index (TI)

LD50 / ED50; indicates drug safety margin

Potency

Amount of drug needed to produce an effect; measured by ED50 shift on DRC

Effectiveness

The maximum effect a drug can produce

Side effects

Any unintended effects; can be harmful or therapeutic depending on context

2nd Rule of Pharmacology

How a drug enters the body affects potency effectiveness and duration

Vehicle

Medium (capsule

Subcutaneous (s.c.)

Injection under the skin; slow absorption

Intramuscular (i.m.)

Injection into muscle; moderate absorption (~60 mins)

Intraperitoneal (i.p.)

Injection into the peritoneum (outside organs); common in lab animals

Intravenous (i.v.)

Injection into vein; very fast absorption (<1 minute)

Intrathecal (i.t.)

Injection into spinal fluid; bypasses blood-brain barrier (BBB)

Intracerebroventricular (i.c.v.)

Injection directly into the brain extremely small doses used

Arteries

Carry blood away from the heart

Veins

Carry blood to the heart

Capillaries

Tiny vessels that allow diffusion of gases nutrients and drugs

Inhalation

Drugs enter through lungs—large surface area fast absorption direct brain route

Smoke vs. vapor

Smoke doesn’t re-vaporize; vaporized drugs (like anesthetics) reach equilibrium quickly

Intrasal (snorting)

Absorbed through nasal mucosa; effects felt in seconds to minutes due to weak BBB

Oral (p.o.) administration

Taken by mouth; absorption depends on solubility and resistance to stomach acid

Rectal administration

Uses GI tract for absorption when oral route isn’t possible

Transdermal

Absorption through skin; slow and steady release (e.g. nicotine patchesfentanyl)

Lipid solubility

Determines how well drugs pass through membranes and BBB

Blood-brain barrier (BBB)

Protects brain; allows only lipid-soluble molecules to pass

Passive transport

Diffusion-based movement through BBB pores or carrier proteins

Active transport

Moves substances across BBB against the concentration gradient

Metabolism

Enzymatic breakdown/inactivation of drugs; produces metabolites

Metabolites

Drug byproducts that may be more or less active or toxic

Enzymes

Proteins (ending in –ase) that break down drugs often in the liver

Factors affecting metabolism

Drug experience age body weight sex/genetics enzyme presence species dosage route and frequency

Purpose of metabolism

Makes drug molecules easier to process and eliminate

Alcohol metabolism

Humans metabolize ethanol uniquely due to enzymes evolved from fruit consumption