Pharmacology for Rehab 1

What is half-life?
The amount of time required for 50% of drug remaining in the body to be eliminated

How are drugs usually eliminated?
By chemically altering original compound while still in body,
By excreting the active form of the drug
By a combo of the two

What is biotransformation?
The chemical changes that take place in the drug following administration (so it is no longer active.)
( also known as Drug Metabolism)

What is excretion?
Removing the active form of the drug from the body

Biotransformation usually results in this altered version of the original compound

What is the primary function of biotransformation?
Drug termination

How quickly does drug biotransformation occur and why
within matter of minutes or hours,
to reduce the chance for toxic effects caused by drug accumulation or prolonged drug activity

What causes the chemical changes that occur during drug metabolism?
oxidation, reduction, hydrolysis, or conjugation of original compound

Occurs when either O2 is added or H is removed from the original compound.
Where are the primary catalysts located?
Oxidation, these enzymes are primarily in smooth endoplasmic reticulum of cells (DMMS)

Predominant method of drug biotransformation in the body

Reactions that consist of removing O2 or adding H;

Drug metabolism in which original compound is broken into separate parts.

Drug metabolism in which the intact drug or metabolite is coupled with endogenous substance.

Phase I chemical reaction
biotransformation reactions consisting of those using oxidation, reduction, or hydrolysis

Phase II chemical reaction
biotransformation reactions involving conjugation of parent drug or the metabolite of a drug that was already metabolized using phase I reaction

How does biotransformation help metabolite excretion from body?
by creating a more polar compound

Primary location for drug metabolism

Organs besides the liver that contain metabolizing enzymes and exhibit considerable drug transformation abilities
lungs, kidneys, gastrointestinal epithelim, skin

What is enzyme induction?
When prolonged use of certain drugs “induces” the body to enzymatically destroy a drug more rapidly

Why does enzyme induction occur?
Usually because either more metabolizing enzymes are being manufactured or less are being degraded.

Why does tolerance to some drugs occur?
Enzyme induction causes drugs to be metabolized more rapidly than expected and decreases the therapeutic effect.

Besides using drugs long term, what else can cause enzyme induction?
long term ingestion or inhalation of alcohol, smoking, or environmental toxins

Primary sites for drug excretion

Where is the metabolized or conjugated version of the original drug filtered?
in the glomerulus after filtration in the nephron

What kind of drugs will be excreted in significant amounts by the kidneys? Why?
relatively polar drugs or their metabolites, because the ionized metabolite has a greater tendency to remain in the nephron and not be reabsorbed into the body

2 primary measurements used to indicated the rate at which a drug is eliminated in order to adjust dosage accordingly
clearance and half-life

2 factors in calculating clearance from a specific organ
the blood flow to the organ
the fraction of drug removed from the plasma as it passes through the organ

Clearance is dependent on what?
The tissues ability to extract the drug from the plasma and the perfusion of the organ

Primary factors responsible for variations in the response to drugs
Genetic variations, disease, drug interactions, age, diet, sex

Why do some of the most serious problems occur during drug interactions? Ex.
Because one drug delays the biotransformation of the other. Tagamet/coumadin. Tagamet delays metabolism of coumadin

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