PHARMACOLOGY

♦ What is Pharmacology?

The study of how drugs interact with a living system.

Pharmacology Two Types:

Pharmacodynamics: ( Effect of the drug on the body ).
Pharmacokinetics: ( Effect of the body on the drug ).

Pharmacology:

Pharmacokinetics: “what the body does to the drug.”

a. Absorption
b. Distribution
c. Metabolism
d. Elimination

Pharmacodynamics: “what the drug does to the body.”

a. Wanted effects – Efficacy
b. Unwanted effects – Toxicity

The drug at the site of administration:

Disintegration:

Disintegration is the process in which a tablet is fractured into small particles.

Dissolution:

Dissolution is the process where solid substances enter a solvent to yield a solution.

Absorption:

This is the percentage of the

Dose absorbed from the

gastrointestinal tract after

oral administration. This

varies from drug to drug.

» Drugs are frequently administered orally.

» Other routes:

✓ Intravenous

✓ Subcutaneous

✓ Intramuscular

✓ Topical

✓ Inhalation

✓ Per rectal

Transport of a drug from the GI tract:

Depending on their chemical properties.
Drugs may be absorbed from the GI tract by either

1. Passive diffusion or

2. Active transport

Two types of absorption:

Passive diffusion: Active transport:

1. Drug moves from a region of high concentration to lower concentration.

2. Does not involve a carrier

3. Not energy-dependent

1. Drug moves from a region of low concentration to higher concentration.
2. Involves specific carrier proteins.
3. Energy-dependent ( adenosine tri-phosphate )

Peak plasma concentration (Cmax):

The highest concentration of a drug achieved in the blood after a dose.

Tmax:

The time after administration of a drug when the maximum plasma concentration is reached when the rate of

absorption equals the rate of elimination.

Minimum effective concentration(MEC):

The minimum quantity of a drug required to produce a particular effect.

Area Under Curve (AUC) :

Availability of a drug in the body for a given period.

Greater AUC ~ Better for patient

Half-life:

The half-life( t1/2 ) is the time at which the peak plasma concentration of a drug in the body reduces by 50%.

Minimum Bactericidal Concentration (MBC):

It is the minimum concentration of an antibiotic in the blood that can kill micro-organisms.

Minimum Inhibitory Concentration (MIC):

It is the minimum concentration of an antibiotic in the blood that can inhibit the growth of micro-organisms.

Lower MIC, Higher peak serum concentration; More powerful antibiotic.

Drug Distribution:

The process by which a drug reversibly leaves the bloodstream and enters the extracellular fluid and the cells of the tissues.

Reversible binding of drugs to plasma protein
Non-diffusible form ( protein-bound fraction )
Slows their transfer out of the blood vessel
Plasma albumin is the major drug-binding protein.

Drug Metabolism:

Chemical transformation of drugs that occur within the body
Metabolites: Any substance produced by metabolism.

First Pass effect/Pre systemic metabolism:

When a drug is taken by mouth, it is absorbed. Next, it passes through the liver, and then it enters into circulation. In the liver, the drug may or may not be metabolized. This process is called the First Pass effect.

It tells us how much of a drug will reach the inactive circulation form.

Bioavailability:

The rate and extent at which the drug reaches the systemic circulation.

Drug Interaction:

When the even pharmacological action of one drug is affected by another drug taken simultaneously, the effect is known as a drug interaction.

Efficacy:

Efficacy is the maximal response produced by a drug.

Potency:

Amount of drug required to produce a particular response. The lower the Dose needed for a given response, the more potent the drug.

Drug receptors :

Drug receptors:

Specialized target molecule, present in the cell surface or intracellularly, that binds with a drug and

mediates its pharmacological actions.

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Drug

Drug Receptor Mechanism:

Affinity: Tendency of a drug to combine with the receptor.

Agonist: A drug that has both Redep bar efficacy and affinity for the receptor.

Antagonist: A drug that has an affinity for a receptor but lacks efficacy.

Toxicology: The untoward effect is death in toxicology.

Toxic Dose: is the Dose causing symptoms of poisoning or untoward effect in an average individual.

Lethal Dose (LD): is the Dose causing the death of experimental animals in a short period under controlled conditions.

ED50: The Dose at which 50% of the experimental animal shows a maximum therapeutic response.
LD50: is the minimum dose required to kill 50% 0f the test animals in 24 hours in controlled conditions.

Therapeutics: The science dealing with the use of medicine for treatment is therapeutics.

Therapeutic ratio: The figure obtained by dividing the LD50 by therapeutic Dose is known as the therapeutic ratio. Obviously, the higher this ratio, the safer is the drug to use.

Materia Medica: The science of source of the drug is called Materia Medica

Therapeutic Index toxic dose/effective dose:

The ratio of the Dose that produces toxicity to the Dose that provides a clinically desired or effective response.

Significance of therapeutic Index: It is a measure of the drug’s safety since a considerable value indicates that there is a wide margin between doses that are effective and doses that are toxic.

Excretion:

Elimination of drugs from the body after being partly or wholly converted to water-soluble metabolites.

Skin (sweating), Lungs, Intestine (stool), Urinary System (urine)

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