Introduction to Pharmacology

Pharmacology is the science of dealing with all drugs, legal or illegal, and their
actions on living organisms.
Drugs / Medications – chemical substances that have an effect on living organisms,
used to diagnose, prevent, control, and/or cure a condition or disease.
Sources of Drugs
1. plants
2. animals
3. synthetic

Drug Names
chemical name – shows the chemical component of the drug
generic name / common name / nonpropriety name – simpler name of the drug.
official name – the name under which the drug is listed in official publication such as
FDA.
brand name / trademark name / propriety name – registered name of the drug
given by its manufacturer.

Drug Classification
1. Body system they effect e.g. respiratory drugs, cardiovascular drugs
2. Therapeutic use or clinical indication e.g. antacids, antibiotics, antihypertensives
3. Physiologic or chemical action e.g. beta-blockers, cholinergics
4. Prescription or Nonprescription (OTC)
5. Therapeutic drugs or Illegal/recreational drugs
Categories of Drug Action:
1. Stimulation
2. Depression
3. Replacement
4. Irritation
5. Inhibition or killing of organisms
Therapeutic Action of Drugs
1. Curative – treat the disease itself e.g. antibiotic for infection
2. Supportive – sustains body function until other treatment or until body’s
response can take over e.g. Mannitol to reduce ICP
3. Palliative – relieves signs and symptoms of a disease but will not affect the
disease itself e.g. anti-inflammatory drugs.
4. Substitutive – replaces body fluids or substances e.g. insulin for DM

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 5. Chemotherapeutic – destroys malignant cells e.g. cyclophosphamide for
prostate cancer
6. Restorative – returns the body to health e.g. multivitamins

General Properties of Drugs

• Drugs do not confer any new function on a tissue or organ in the body. They
only modify existing functions.
• For a drug to take effect in the body, it must bind to its receptor first.
• The better the fit between the receptor and the drug the stronger the action of
the drug.
• Drugs that interact with the receptor to stimulate a response is called an agonist.
• Drugs the interact with the receptor to block the response is called an antagonist
or blocker.
• Drugs in general exert multiple actions rather than a single effect. Therefore, no
drug is free from side effects.
• Drug interaction results from physiological interaction between a drug and
another drug.

DRUG ACTION
The three phases are:
1. Pharmaceutic - the first phase of drug action where the drug becomes a
solution so that it can cross the biologic membrane
2. Pharmacokinetics – the process of drug movement to achieve drug action.
3. Pharmacodynamics – the study of the way drugs affect the body.

I. Pharmaceutic phase
It involves:
1. Disintegration – a process where a drug in solid form like tablet disintegrate
into small particles.
2. Dissolution – dissolving of smaller particles in the GI fluid before absorption.
Drugs in liquid form are already in solution.
Rate-limiting – the time it takes the drug to disintegrate and dissolve to become
available for the body to absorb it

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Factors Affecting the Pharmaceutic Phase
1. Excipients – fillers and inert substances which allow the drug to take on a
particular size and shape and to enhance dissolution.
2. Additives – increases the absorbability of the drugs e.g. potassium (K) and
sodium (Na)
3. pH – drugs are both disintegrated and absorbed faster in acidic fluids (pH 1 or
2)
4. Enteric-coated drugs – resist disintegration in the gastric acid of the stomach.
Disintegration does not occur until the drug reaches the alkaline environment of
the small intestine.
*Enteric coated tablets or capsules and sustained-release (beaded) capsules
should not be crushed. Crushing would alter the place and time of absorption of
the drug.
5. Food – interferes with the dissolution of certain drugs.

II. Pharmacokinetic Phase

Processes of drug movement to achieve drug action:
1. Absorption
2. Distribution
3. Metabolism / Biotransformation
4. Excretion / Elimination

ABSORPTION
• Refers to the time the drug enters the body until it enters the bloodstream or
lymphatic fluid.
• Movement of drug particles from the site of entry to the circulation by passive
absorption, active absorption or pinocytosis.
Factors Affecting Absorption
1. Blood flow – drugs are absorbed faster in body areas with more blood vessels
or rich blood supply. IM injection promotes faster absorption of the drug than
subcutaneous injection.
2. Pain and stress– slows down gastric emptying time that the drug remains in
the stomach longer.
3. Food – solid, hot and high in fat decreases absorption of the drug.
4. Exercise – decreases blood flow to the GIT by causing blood to flow to the
peripheral muscle thereby decreasing absorption.
5. pH – acidic drugs are best absorbed in acidic environment and alkaline drugs are
best absorbed in an alkaline environment.
6. Route of administration – drugs that do not pass the GI tract or liver such as
drugs administered parenterally or topically are absorbed faster.

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 7. Ionization – nonionized drugs (have no positive or negative charge) are
absorbed faster than ionized drugs.
8. Solubility – lipid soluble medications are absorbed faster that water-soluble
medications
9. Drug concentration- drugs administered in high concentration tend to be more
rapidly absorbed. Bolus dose of drugs produce rapid effect.
10. Drug formulation – an active drug may be combined with another substance
from which it is slowly released or may be prepared in a vehicle that offers
relative resistance to the digestive action of the stomach contents.
First-pass effect / Hepatic first pass – the process in which the drug passes to the
liver first where the drug may be metabolized to an inactive form that may then be
excreted, thus reducing the amount of active drug.
Bioavailability – percentage of the administered drug dose that reaches the systemic
circulation.
The percentage of bioavailability for the oral route is always less than 100% but for the
intravenous route, it is always 100%. Thus, the oral dose could be higher that the drug
dose for IV use to achieve the desired drug effect.
A decrease in liver function or a decrease in hepatic blood flow can increase the
bioavailability of the drug.
Rapid absorption of some oral drugs increased the bioavailability of the drug an can
cause an increase in drug concentration which may eventually lead to drug toxicity.

DISTRIBUTION
• The process by which the drug becomes available to body fluids and tissues.
Factors Affecting Distribution
1. Blood flow – increased blood supply enhances distribution
2. Drug’s affinity to tissue – the drug attaches to receptor sites for the
pharmacological response to take place. Agonist tend to bind with receptor sites
and exerts its action while antagonist cause uneven attachment producing no
response. When more than one drugs is administered, these tend to compete to
bind with receptor sites which may decrease its effect.
3. Protein-binding effect – Drugs in plasma tend to bind with protein (primarily
albumin) in varying degrees. The portion of the drug that is bound to protein is
inactive because it is not available to receptors, and the portion that remains
unbound is free active drug. Only free active drug exerts a pharmacologic
response.
**To avoid possible drug toxicity, the nurse should check the patient’s plasma
protein and albumin levels and determine the drug’s protein binding percentage.

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 A decrease in plasma (albumin) decreases protein-binding sites, permitting more
free drugs in the circulation.
4. Abscesses, exudates, body glands and tumors hinder drug distribution.
5. Body weight – obesity affects distribution because blood flows through fat
slowly thus increasing time before drug is released.
6. Volume of drug distribution (Vd) – Vd is dependent on drug dose and its
concentration in the body. Drugs with a larger volume of drug distribution have a
longer half-life and stay in the body longer.
**Clients with edema requires higher drug dose while those with dehydration
may need a smaller dose.
7. Barriers to drug distribution – prevents entry of drugs to certain body parts.
a. Blood Brain Barrier (BBB) – a semipermeable membrane in the CNS
that protects the brain from foreign substances. Highly lipid soluble drugs
can cross the BBB.
b. Placental Barrier – during pregnancy, drugs may pass through the
placental barrier which may cause adverse effects to the fetus
(teratogenic effect)

METABOLISM
• The process by which the body inactivates or biotransform drugs.
• The liver is the primary site of metabolism.
• Metabolism of medications may cause its inactivation to facilitate excretion.
However, some medications will be metabolized to its active form which
increases pharmacologic response.
• When the drug metabolism rate is decreased, excess drug accumulation can
occur and lead to toxicity.

EXCRETION / ELIMINATION
• The process by which drugs are eliminated from the body. The main route of
drug elimination is through the kidneys (urine). Other routes include bile, feces,
lungs, saliva, sweat and breast milk.

Factors Affecting Excretion

1. Urine pH – acidic urine promotes elimination of weak base drugs and alkaline
urine promotes elimination of weak acid dugs.
2. Renal function – kidney disease that results in decreased glomerular filtration
rate (GFR) or decreased renal tubular secretion slows down or impairs drug
excretion. Creatinine clearance and Blood Urea Nitrogen (BUN) are kidney

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 function tests to detect problems in excretion. A decrease in GFR results in an
increase serum creatinine level and a decrease in urine creatinine clearance.
3. Blood concentration levels – when peak level of the drug is reached,
excretion levels become greater than absorption and blood levels of drugs begin
to drop.
4. Drug interaction – drugs can affect elimination of other drugs. A drug may
promote or prevent excretion of another drug which are received at the same
time.
5. Half-life (t ½) – the time it takes for the half of the drug concentration to be
eliminated. This determines appropriate drug dose and frequency of
administration. A short half-life is considered to be 4 to 8 hours, and a long half-
life is 24 hours or longer. Metabolism and excretion affect the half-life of a drug.

III. Pharmacodynamic Phase

Drug response can cause primary or secondary physiologic effect or both. The primary
effect is desirable, intended effect while the secondary effect may be desirable or
undesirable.
1. Dose Response – the relationship between the minimal versus the maximal
amount of drug dose needed to produce the desired drug response.
2. Maximal Efficacy – refers to the maximum drug effect.
3. Onset of action – the time it takes to reach the minimum effective
concentration (MEC) after a drug is administered.
4. Peak action – occurs when the drug reaches its highest blood or plasma
concentration.
5. Duration of action – the length of time the drug has a pharmacologic effect.
6. Therapeutic Index (TI) – estimates the margin of safety of a drug through
the use of a ratio that measures the effective (therapeutic) dose (ED) in 50% of
people (ED50) and the lethal dose (LD) in 50% of people (LD50). The close the
ratio is to 1, the greater the danger of toxicity. A low therapeutic index connotes
a narrow margin of safety while high therapeutic index has a wide margin of
safety.
7. Therapeutic Range / Therapeutic Window – the level of drug between the
minimum effective concentration in the plasma for obtaining desired drug action
and the minimum toxic concentration (the toxic effect).
8. Peak drug level – the highest plasma concentration of the drug at a specific
time. It indicates the rate of absorption of the drug.
9. Trough drug level – the lowest plasma concentration of a drug. It indicates the
rate of elimination of the drug
10. Loading dose – a large initial dose given to achieve a rapid minimum effective
concentration in the plasma.
11. Desired effect / Therapeutic effect – primary effect or intended effect of the
drug. It is the reason the drug was prescribed.

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 12. Side-effects – are secondary unintended effects; physiologic effects not related
to desired drug effects.
13. Adverse Reactions – are more severe than side-effects; a range of untoward
effects (unintended and occurring at normal doses) of drugs that cause mild to
severe side effects. Adverse effects must always be reported and documented.
14. Toxic Effects / toxicity – when the drug level exceeds the therapeutic range,
toxic effects are likely to occur from overdosing or drug accumulation. It occurs
when a drug is eliminated more slowly than it is absorbed, causing excessive
drug concentration.
15. Allergic or hypersensitivity reaction – an immunologic reaction to the drug.
16. Anaphylactic reaction – a severe, life-threatening allergic reaction that causes
respiratory distress and cardiovascular collapse.
17. Idiosyncratic effect – it is the unusual, abnormal response to the drug; it is an
unexpected, unpredictable or unexplained response.

DRUG INTERACTIONS

The action of one drug is altered by the action of another drug by altering the
pharmacokinetics of a drug.
Combination of two agents may increase or decrease the action of one or both drugs
which can be beneficial or harmful.
Types of Drug Interactions:
1. Additive Effect (Summation) – the combined effect of two drugs produces a
result that equals the sum of the individual effects of each drug.
2. Synergistic Effect (Synergism / Potentiation) – The combined effects of
drugs is greater than the sum of each individual agent acting independently.
3. Cumulative Effect – It is the increasing response to the repeated doses of a
drug that occurs when the rate of administration exceeds the rate of metabolism
or excretion.
4. Antagonistic Effect (Antagonism) – Conjoint effect of two drugs is less than
the drugs acting separately. Each drug cancels the effect of the other.