History of Pharmacology effects of intravenous injection of ipecac, morphine,

The discovery and development of pharmacology was strychnine, hydrocyanic acid, iodine, and quinine, and many
one of the greatest advances in the medical milieu. Eliminating more drugs. He also published the Formulary.
the ancient ways of practical healing procedures such as 6. Claude Bernard (1813 – 1873), Schmiedeberg – revealed
endowment of sacrifices from plants and animals to appease the primary pharmacological action of the drug was exerted
a wrathful spirit, drug usage was established. on the heart.
A. Ancient Era 7. M.J.B. Orfila – the founder of Science of Toxicology. He
1. Apollo – Greek God of Healing conducted Toxicologic Generale and systemic investigation of
2. Asclepius – the son of Apollo, whose priest physicians poisonous substances.
founded temples of healing where disease people were
treated by prayer, mineral spring baths, and massage. C. Origin of General Pharmacology
3. Pen Tsao (2700 B.C.) – earliest recorded compilation of 1. S. Dale (1692) - coined “Pharmakologie” as science of
drugs consisted of list of herbal remedies compiled in the reign Materia Medica.
of Chinese Emperor Shennung 2. City of Dorpat in Baltic Sea – the birthplace of Pharmacology
4. Ebers papyrus (1150 B.C.) – first written record of drugs, which was established in the University of Dorpat during 1846
which are composed mostly of prescriptions for specified and with laboratory devoted for experimental pharmacology.
ailments, and the substances and procedures to be used for 3. Rudolph Buchheim (1846) – a biochemist professor at the
treatment. University of Dorpat and was known the Father of
5. Greek Philosophers – Physicians (500 B.C.) – proposed and Pharmacology. He considered necessary to explain the action
taught the concept that health was maintained by a balance of drug upon the organs and cells of the body (evidence-based
of the body humor, which was influenced by heat and cold, pharmacology).
moisture and dryness, acidity and sweetness and disease was 4. Oswald Schmeideberg (1838 – 1921) – the most
due to imbalance by these qualities. outstanding student of Buchheim while later succeeded him at
6. Hippocrates (460 – 370 B.C.) – proposed to have originated the University. He defined pharmacology as an “experimental
the theory that disease is due to imbalance of the body humor science” which has for its purposes the study of changes
(Humoral Pathology) rather than the gods and demons. He is brought about in living organisms by chemically acting
considered the Father of Medicine. substances (except for food, whether used for therapeutic
7. Dioscorides (77 A.D.) – pupil of Aristotle who wrote the first purposes or not).
Materia Medica (Materials of Medicine) which was principally 5. John Jacob Abel (1857 – 1938) – one of the students of
the qualitative classification of medicinal herbs but included Schmeideberg who became the father of American
mineral and few animal origins. Pharmacology.

B. The Renaissance Period

1. Paracelsus (1492 – 1541) - wrote, “Reading never made a
physician. Medicine is an art that requires practical D. Origin of Veterinary Pharmacology
experience.” ⮲ The first record was when archeologist unearthed the ruin
2. William Harvey (1578 – 1657) – discovered the phenomena in India of an army hospital only for horses and elephants
of circulation. This observation was followed by the injection dating back 5000 B.C.
of water, colored fluids, ink and wax into the blood vessels of ⮲ Great epizootics decimated animal population in Western
animals. Europe, especially in cattle. In response during 1760’s, five
3. Sir Christopher Wren (1656) – made the first intravenous veterinary colleges were established in France, Austria,
injection of drug (opium) using a dog. Germany, and Netherlands, and in 1791 Veterinary College
4. William Withering (1783) – an English physician, reported started in London, England.
on his experience in the use of crude digitalis for the treatment
⮲ In United States, it was started in Philadelphia (1852) and
of “dropsy”.
Boston (1854).
5. Francois Magendie (1783 – 1855) – a French physiologist –
pharmacologist published experimental observation on the
Pharmacology Defined
 • The term Pharmacology is derived from the Greek ⮲ Is concerned with the study of basic mechanism of drug
words pharmakon, “drug or poison” and logos, action on biological systems
“study” and means the science of drugs and their ⮲ Aims to determine and interpret the relationship between
interaction with living organism. biologic activity and the structure of molecules or group of
• Pharmacology is both a basic and clinically applied molecules.
science 2. Clinical Pharmacology
⮲ Is most concerned with the rational development, effective
Purposes of Pharmacology use, and the proper evaluation of drugs for the diagnosis,
As a pure science, the purpose of pharmacology is to prevention, and cure of diseases
determine the response of living organisms to chemical stimuli
⮲ Also deals with the safe use of drugs in any animal species
in the presence or absence of disease.
including human beings.
⮲ The principles of clinical pharmacology apply to both animal
As an applied or practical science, it has the following
and human medicine.
functions:
3. Veterinary Pharmacology
1. To test the drugs quantitatively and standardize them so
⮲ Is concerned with drugs as they are used in the diagnosis
that they are available to the doctor and patient in uniform
and treatment of animal diseases, and in the intentional
and dependable forms
alteration of animal physiology.
2. To determine how drugs produce their effects on the animal
⮲ The range of animal species, in which drugs are used and
body
studied, distinguishes veterinary pharmacology from medical
3. To develop new drugs
(human) pharmacology.
4. To establish rational and safe dosaging

The Drug
Divisions of Pharmacology
Pharmacology is one of the youngest of the medical sciences,
Pharmacology consists of four divisions:
but the use of drugs is as old as humanity.
1. PHARMACODYNAMICS – is the science and study of how
drugs produce effects on living organism.
Pharmacokinetics” (from the Greek word pharmakon –
“drugs” and kinetikos – “putting into action”) which is the
science and study of the processes
Pharmacokinetics is divided into several areas, which includes
the extent and rate of Absorption, Distribution, Metabolism
and Excretion (ADME) or Liberation, Absorption, Distribution,
Metabolism and Excretion (LADME)
2. TOXICOLOGY – is the study of harmful effects of drugs, and
the conditions under which these harmful effects occur
3. PHARMACOTHERAPEUTICS – (or simply therapeutics) refers
to the application of drugs for use in the diagnosis, prevention,
and treatment of diseases, and in the purposeful alteration of
normal body functions.
4. PHARMACY - is the art and science of preparing,
compounding, and dispensing of drugs. It includes:
⮲ Pharmacognosy – the study of sources of drugs

⮲ Posology – the study of drug dosage

⮲ Metrology – deals with weights and measures

Categories of Pharmacology
1. Molecular Pharmacology Table1. Historical Trace of the Development of Therapeutics
Drug Definition ⮲ Aspirin taken at a proper does relieves pain, fever, and
The term drug is thought to originate from Old French inflammation, but an overdose of it may cause, among others,
"drogue", possibly deriving later into "droge-vate" from stomach ulcers and blood disorders.
Middle Dutch meaning "dry barrels", referring to medicinal ⮲ Warfarin, a popular rat poison, kills rats by causing internal
plants preserved in them. bleeding due to blockade of the normal utilization of vitamin
Consider two agents: Heat and a Chemical Wood Preservative K.
⮲ Heat from a hot compress may be applied on a sprained
joint to ease the pain and inflammation. Although it affects the Selective Toxicity
patient (a living organism), heat cannot be considered a drug Define as a given dose of a drug may be poisonous to one
for it is not a chemical agent. organism but not to another. Selective toxicity has been put
⮲ The wood preservative is a chemical, but it is applied on to good use in the treatment of infections and cancers and is
non-living object (wood). Can we consider the preservative a the basis of chemotherapy.
drug? It should be realized that the wood is preserved because The effect of a drug is therefore quantitative and never been
the chemical kills or prevents the growth of bacteria, molds, qualitative. Quantitative since drugs may only enhance or
termites, and other living organisms that cause wood decay. reduce the functions (changing the intensity or magnitude of
Since the wood preservative affects these living organisms body functions) of which the organism naturally capable and
that cause wood decay, it is therefore considered a drug. not to change the nature of an existing body function
(qualitative).
Drug Action
When administered to a living organism, a drug may cause a Drug Action versus Drug Effect
response, which may be useful or harmful to the organism. A drug effect refers to what is produced by the drug and drug
However, non-drug substances (e.g. food) may also be action is to where and how the effect is produced.
induced pharmacological effects.
Physiological and Pharmacological Effects MODULE 2
⮲ A substance may induce physiological or pharmacological The Principles of Drug-Receptor Interaction

effect.
⮲ Nutrients, which are not considered drugs (by the broad Specificity of Drug Action

definition), and hormones when taken in or administered in • Drugs may bind to molecules at some sites in the body

excess may produce exaggerated nonspecific effects on the where they do not produce any perceptible effect.

animal. These effects are considered pharmacological. The interaction of drugs with molecules in these sites

⮲ In contrast, an effect that promotes or maintains normal is said to be non-specific. In contrast to the
interaction of drugs with receptor molecules in their
body functions is considered physiological. ⮲ Examples: Water
site of action produces perceptible change in the
and insulin
function of an organism. This drug – receptor
o Water is normally taken as part of food.
interaction is said to be specific.
o Insulin is a hormone essential to glucose uptake by most
• If the chemical structure of the drug is altered, its
body cells; it is use in the treatment of diabetes mellitus.
specific interaction with the receptor is modified
resulting in the change in the intensity of effect. This
Every Drug Is a Poison
is called the structure-activity relationship (SAR).
Philippus Aureolus Theophrastus Bombastus von Hohenheim
(or Paracelsus), considered the grandfather of
Drug Receptor
pharmacology, said that “all substances are poisons; there is
• Majority of drugs must combine with some key
none which is not a poison. The right dose differentiates a
substances in the biological system that has an
poison and a remedy (medicine)”.
important regulatory function in the target tissue or
Take aspirin and warfarin as an example:
organ. This biological partner of the drug is called
receptive substance or drug receptor.
 • A drug receptor is any cellular macromolecule • Not all drugs require receptors to produce an effect .
present in cell membranes that a drug binds and Some drugs cause alteration in organisms by virtue of
when activated initiate its effects. their general nonspecific properties rather than by
• The usual concept for drug receptor is that only when interaction with specific receptors. Examples are
the receptor is occupied by the drug its function anesthetics (volatile anesthetics), antacids, chelators,
transformed in such a way as to elicit a response. This and osmotic agents.
concept is known as the occupation theory.
• Any drug or substance with specific affinity to Drug Activity
receptors is called a ligand. • When a drug molecule interacts with a drug receptor,
a drug receptor complex is formed, which then
Nature of Drug Receptor triggers the formation of a stimulus to produce an
• The exact chemical nature of most receptors is not effect.
known but indications are that they are made of • In the formation of a drug – receptor complex, the
proteins, lipids, and carbohydrates. Proteins form the drug and the receptor become one entity (at least
most important class of drug receptor. Receptors temporarily) which is quite different from either the
have a ligand-binding site and an effector site drug or the unoccupied receptor. Without this
analogous to those of enzymes. alteration, no drug effect may be produced.
Types of Receptors and the Mechanism by which they Produce Two Basic Requirements for Drug Activity: Affinity for the
Pharmacologic Response receptors and Intrinsic Activity
1. Ion – Channels 1. AFFINITY – the tendency of the drug to combine with its
a. Voltage gated ion channels are activated by alterations in specific receptor and is known as the first of the two
membrane voltage. requirements for drug activity. It is analogous to the ability of
b. Ligand gated ion channels are activated after binding to a key to fit into a keyhole of a lock.
specific ligands or drugs. 2. INTRINSIC ACTIVITY – aka “efficacy”, is the inherent
2. G – protein coupled receptors - compose a large class of capacity of the drug to produce an effect. Efficacy is analogous
membrane-bound receptors. The protein structure of these to the ability of the key to open the lock.
receptors includes a common seven-membered a) Agonist – a drug with both affinity and efficacy and will
transmembrane domain. action when it reaches a receptor. Agonist drugs mimic the
3. Receptor tyrosine kinase effect of endogenous compounds.

⮲ Receptors are proteins, found in the cell membrane, b) Partial Agonist – a drug that can elicit some but not a

consisting of an extracellular portion that binds the ligand, a maximal effect and which antagonizes an agonist. It is a drug

transmembrane portion that transmit the signal trough the cell with a favorable affinity but a low intrinsic activity.

membrane, and a cytoplasmic portion that terminates in the c) Antagonist – are drugs that have an affinity for the receptor

cytoplasm. site but lack intrinsic activity. They block or reduce the effects

⮲ The cytoplasmic portion of the receptor possesses tyrosine of agonists.

kinase activity
Drug – Receptor Binding
⮲ These enzyme-linked receptors mediate the responses of
• Any combination of the known chemical bonds may
insulin, epidermal growth factor (EGF), platelet – derived
be involved in the chemical interactions between the
growth factor (PDGF), and other trophic hormones.
drug and receptors.
4. Intracellular hormone receptors - Lipophilic substances
capable of crossing the plasma membrane may activate
Types of molecular bond involved in a drug – receptor
intracellular receptors.
interaction:
1. Covalent Bond – this bond shows two atoms share a pair of
Location of Drug Receptors
electrons. Having a very high binding energy, it is essentially
• Drug receptors are located either on the surface of
irreversible but can be broken at very high temperature, or
cells or within cells. They occupy only a tiny portion of
with an intervention of a catalytic enzyme.
the cell.
2. Ionic Bond – it is a result from electrostatic attraction The blockade may result in perceptible alteration of
between oppositely charged ions. The force of attraction the normal activity of the system perceived as either one of
between ions diminishes inversely with the square of the the following:
distance between them. 1. Decrease effect of endogenous neurotransmitter or
3. Hydrogen Bond – arises from the ability of a proton (H+) to hormone whose receptors are being blocked by the drug.
accept an electron pair: one from a donor (e.g. oxygen) and 2. Enhanced effect of a neurotransmitter or hormone having
the other from another donor (e.g. nitrogen or other oxygen). an opposite effect to that of the blocked neurotransmitter or
An H bond is much weaker than a covalent bond, but the hormone.
presence of several H bonds can stabilize a drug – receptor • Note that the observed pupillary dilatation following
interaction significantly. atropine is not directly caused by atropine; instead, the activity
4. Intermolecular Bond (van der Waals forces or London of norepinephrine since acetylcholine was blocked by the said
forces) – from very weak binds between dipoles or induced chemical agent (atropine).
dipoles, often between similar atoms. • If atropine is applied on an eye from which the influences of
acetylcholine and norepinephrine had been previously
Silent Receptors and Silent Interactions removed, no effect on the pupil would be observed. This
• A drug may combine with molecules other than its proved that atropine has no intrinsic activity and is considered
receptors such as plasma proteins and tissue a full antagonist of acetylcholine.
proteins, but this combination does not result in a
drug effect. The receptors involved in this interaction AGONIST, ANTAGONIST AND DUALIST
are called silent receptors. This has been referred as Agonist
non-specific receptors. The interaction, being ⮲ An agonist is a drug having both affinity and intrinsic activity.
effective, is called a silent interaction (non-specific It is any drug or substance that binds to a specific and by itself
interaction). can produce an effect and does not require the presence of
Acceptor vs. Receptor endogenous ligands.
⮲ An “acceptor” is a chemical substance with which a drug
bind nonspecifically Antagonist

⮲ This binding does not lead to perceptible pharmacological ⮲ An antagonist is a drug that does not have intrinsic activity
effect. but binds with specific receptors and blocks the action of an
endogenous hormone or neurotransmitter or other agonists.
Schematics of Important types of Drug – Receptor ⮲ An antagonist may be competitive or noncompetitive.
Interactions • A competitive antagonist, not having an intrinsic
1. Drug (D) and Receptor (R) interact – changes cell membrane activity, cannot produce an effect except in the
characteristics (stimulus) – brings about action presence of an agonist either of endogenous or
2. Drug and Receptor Interact – Receptor is covered up. But exogenous source
no “lock and key fit”, receptor is blocked. No stimulus – no • A noncompetitive antagonist inhibits the action of an
action agonist by binding at a site other than the binding site
3. Drug interacts with receptors that are not capable of of the agonist to bind with the receptor.
exciting action – silent receptors (SR), a form of binding such • An antagonist is like a key that fits the keyhole but
as plasma protein binding. does not open the lock.
4. Drug interacts with receptor of a drug destroying Enzyme
(E) in liver or plasma. Drug is inactivated.
5. Drug D2 interacts with receptor of the drug destroying Dualist
enzyme in example ⮲ The term dualist refers to a drug having both agonistic and
6. Enzyme is now tied up – action of drug D is prolonged antagonistic properties. Theoretically, intrinsic activity of a
because it is more slowly activated. drug can have any magnitude between zero and maximum (0%
to 100%).
 • The difference between an agonist and antagonist Drug Families
has sense only at the level of receptors found in a A drug family is composed of member drugs which:
specific tissue. For instance, a drug may act as an a. Act on specific receptors in certain effector systems
agonist to a receptor in the smooth muscle of the b. Produce the same kind but different magnitudes of effect
arterioles but may act as an antagonist in similar Not all drugs having affinity to the same receptor belong to
receptors in the brain. the same family.
A group of competitive antagonists having very little or no
Structure – activity relationship has been used in structural similarity to agonists, or to each other may exist.
characterizing drug receptors. In the process of specific drug
receptor interaction only the nature of drug and the resulting Naming of Drug Families
pharmacological response are known. Thus, the nature of drug • Families of agonist are often named after some
receptors is not fully known. However, there are ways by typical members of the group.
which receptors may be studied. ⮲ Examples:
1. Direct Method ▪ Atropine-like agents
⮲ Isolation from tissues ▪ Adrenergic stimulants (adrenaline-like) agents
o Isolation of receptors may be the best method but its seldom ▪ Morphine derivatives
feasible ▪ Barbiturates (derivatives of barbituric acid)
o Isolation techniques almost always alter the nature of the • They may also be named according to their
receptors, such that the receptor properties observed from chemical structures.
isolated receptors do not necessarily reflect those of receptors ⮲ Examples:
in situ. ▪ Benzodiazepines
⮲ Biochemical and physical procedures require the use of ▪ Nitroimidazoles
highly technical methods such as: ▪ Salicylates
o Electron spin resonance (ESR) ▪ Salicylanilides
o Fluorescence ▪ Xanthine derivatives
o High resolution electronic microscopy • Families of antagonist may derive their names from
o Nuclear magnetic resonance (NMR) typical members of their corresponding agonists.
o X-ray crystallography ⮲Examples:
2. Indirect Methods ▪ Antihistamines (vs. histamine)
⮲ This method is commonly employed in the study of ▪ Anticholinergics (vs. acetylcholine)
receptors ▪ Adrenergic blocking agents (vs. adrenaline or noradrenaline)
⮲ Inferences about the receptors are drawn from the results • In practice, always remember that a drug may have
of specific drug-receptor interactions. affinity to more than one kind of receptor.
⮲ The study of the influence of the chemical structure of a ⮲ For example, epinephrine acts on both β - adrenergic and α-
drug on its activity (called structure-activity relationship or adrenergic receptors.
SAR) has been a powerful tool, although indirect, in the study
of the nature of drug receptors. • Drugs having similar indication or clinical use may
not necessarily constitute a drug family.
General Procedure in SAR Study ⮲ Examples:
In a typical SAR study, an appropriate biologic response to a ▪ Atropine, attapulgite and loperamide are all used to control
prototype (parent) drug is identified for the study. The diarrhea, but each belongs to a different drug family.
prototype is then modified structurally by removing, adding,
or substituting chemical groups. The list of these modified
compounds generates a congeneric series.
MODULE 3 • The types and condition of effector system,
The Dose-Response Relationship • The initial drug effect on the effector system, and
The Graded Dose-Response Relationship • The local and systemic contra regulation of the
It is a dose-relationship response that when an increase in the response
dose produce increases in response. ⮲ For instance, the presence of competitive antagonists
Graded dose – response curves have four characteristic reduces the response to the drug (molecular antagonism).
variables: ⮲ The simultaneous stimulation, by separate mechanism, of a
a. Potency – this refers to the dose (concentration) of a drug
physiological process (e.g. dilatation) which is opposed to the
needed to produce an effect. The smaller the dose
drug effect will likewise reduce the response (e.g.
to produce the effect, the greater the potency.
constriction). This is called physiological antagonism.
b. Slope – is of both practical and theoretical importance.
A stimulus produced following the formation of the
c. Variability – in the response can be expected from a specific
drug-receptor complex is a purely theoretical magnitude. It is
dose, and variation in dosage maybe required producing a
simply an aspect of the interaction of an agonist with its
given response.
receptors.
d. Maximal Effect – is the maximum response possible for the
The magnitude of the stimulus is directly proportional to the
effector.
number of occupied receptors.
⮲ Also known as the ceiling effect or plateau In conclusion, a drug may pass through several
processes that can modify its final effect on the patient.
Drug – Receptor Interaction and the Response to Drug Therefore, the study of dose-response relationship in an intact
At this point, it can be assumed that the magnitude of the animal may be so complicated that it is more convenient to do
observed response to drug reflects the extent of drug – away with as many of the variables as possible by using
receptor combination. This means that the magnitude of the isolated effector system.
response is directly proportional to how many drug-receptor
complexes (DR) are formed. If less Drug-receptor complexes The Quantal Dose-Response Relationship
are formed, there would be less response; more DR formed, In the graded-response relationship, the elicited
there would be greater response. response could be measured in a continuous scale. That is, the
THRESHOLD DOSE – it is the lowest concentration of a rate of response of a single biological unit increases with
chemical substance that brings about response. increasing dose of the drug. There are, however,
pharmacological responses which cannot be considered
A Brief Description of the Process Affecting Drugs from the graded. They either occur in full or do not occur at all (all-or-
Time of Administration to the Production of Response in an nothing response).
Intact Animal Following its administration, a drug is absorbed In an all-or-nothing response, also known as quantal
from the site of administration into the blood circulation. The response, an individual unit of a system responds to a drug
rate of absorption is influenced by: dose either maximally or not at all.

The physicochemical properties of the drug including rate of

dissolution, lipid solubility, etc., and The blood flow through The Nature of Quantal Dose-Response Relationship
the site of absorption (less blood flow to the gut; less drug In the quantal dose-response relationship, the frequency in
absorbed). which a dose of a drug produces a stated fixed
The extent and rate of distribution pharmacological effect in population occurs. This can be done
The non-specific binding of drug with tissue and plasma by administering progressively increasing doses of a drug to
proteins, and subsequent liberation of the drug from these groups of animals and recording the percentage of those
reservoirs responding to the drug.

Following the formation of drug-receptor complex, a stimulus

must be formed. The formation of the stimulus may be
influenced by:
 a means of quantitating ADME (absorption, distribution,
metabolism, and
excretion) parameters. Thus, pharmacokinetic processes,
affect the route of administration, doses, dose intervals, and
toxicities of drugs given to animals.

General Principles of Drug Administration

Drug administration – it refers to how a chemical substance
(drugs) is introduced in a species and fundamentally crosses
several biological barriers to reach its site of action and
produce the drug response.

Routes of Administration
All routes of administration except intravascular
involve an absorption process in which the drug must cross
one or more membranes before getting into the blood.
1. Alimentary routes or Enteral routes
• Oral (per os, PO)
Advantages
✓ Usually the safest, convenient, economical, but some
Quick Note!!!
animals are difficult to administer this way ✓ May require the
The Quantal Dose-Response Relationships are used to
drug to be mixed in the food to facilitate administration
establish the useful drug effect and the toxic drug effect
✓ Food may stimulate bile secretion, which will help dissolve
curves. Parameters that can be derived from Quantal dose-
lipophilic drugs to increase absorption Disadvantages
response curves
✓ Acidic environment of stomach and digestive enzymes may
1. The Median (median)Dose
destroy the drug
• Corresponds to the midpoint of the curve
✓ In ruminants, the bacterial enzymes may inactivate the drug
• May also be called effective (ED50), lethal (LD50),
toxic (TD50), Inhibitory (ID50), etc. depending upon ✓ Some drugs may irritate the GI mucosa

the situation The smallest dose required to produce ✓ The presence of food may adversely alter absorption

a stated effect in 50 percent of the population ✓ Some drugs are extensively metabolized by the GI mucosa
2. The Standard Deviation and the liver before they reach the systemic circulation and
• Determines the spread of the population about the this phenomenon is referred as first-pass effect.
mean ✓ Antimicrobials may alter the digestive process in ruminants
• Its calculation is based on the difference between and other herbivores
each observation from the mean value • Sublingual or Buccal – drug is placed under the tongue
Advantages
MODULE 4 ✓ Rapid absorption
Drug Pharmacokinetics ✓ Drug stability
Veterinary pharmacology focuses on drugs that are used in
✓ Avoid first-pass effect
domestic animals. As mentioned earlier, pharmacology is the
Disadvantages
study of the properties of chemicals used as drugs for
✓ Inconvenient
therapeutic purposes, which is divided into pharmacokinetics
✓ Small doses
and pharmacodynamics. The latter focuses on how most drugs
✓ Unpleasant taste of some drugs
affects the body (mode of action), while the former focuses on
✓ Drug is rapidly absorbed into the bloodstream
what the body does to the drugs. Pharmacokinetics provides
✓ Drug must remain under the tongue until dissolved and ✓ Cold – Delayed that rate of absorption
absorbed ✓ Hyalurinadase - increase the rate of absorption
• Rectal ✓ Massaging the site of infection – increase the rate of
Advantages absorption
✓ Can be used in the unconscious animal and in those vomiting

✓ Absorption is slower compared to the intramuscular route 3. Other routes

✓ There are some drugs like diazepam and phenytoin that • Inhalation

have an erratic oral absorption and are better given rectally Advantages

✓ In dogs, influence of the first-pass effect is reduced because ✓ It is used for volatile or gas anesthetics

the rectal veins bypass the portal circulation and go to the ✓ Response is rapid because of the large surface area of the
caudal vena cava (circumvent the GI Tract). lungs and large blood flow to the lungs
2. Parenteral routes ✓ It is reversible if the anesthetic is turned off and the animal
Examples ventilated
• Intravenous Disadvantages
• Intramuscular ✓ Most addictive route of administration because it enters the
• Subcutaneous brain so quickly
• Intraperitoneal ✓ Difficulties in regulating the exact amount of dosage
• Advantages ✓ Patient having difficulties in giving themselves a drug by
• Spinal and subdural Intrapleural inhaler
• Intraarterial ✓ Lung-based transfer may get drug to brain in as little as five
• Intrasynovial seconds.
• Intraconjunctival • Dermal or topical
• Intratracheal
✓ Degree of absorption is dependent on the drug’s lipid
Advantages
solubility
✓ Rapid onset (IV > IM > SC), may be useful in unconscious or
✓ Abraded or damaged skin may be expected to absorb more
vomiting patient, absorption is more uniform and predictable
drug than intact skin
✓ Absorption from IM and SC injection sites is mostly
✓ Animals with thin skin may absorb drugs like corticosteroids
determined by the amount of blood flow to that
readily if they are applied topically than
site. The absorption of local anesthetics is often purposely
animals with thicker skin
slowed by co-administration with epinephrine, which
✓ It is convenient and allows nonskilled operators to
decreases the blood flow to the injection site
administer the drugs by pour-on methods
Disadvantages
✓ Asepsis is necessary
A drug is administered to an animal to bring about systemic
✓ Cause pain or local effect.
✓ May penetrate a blood vessel during IM injection • A local effect is not preceded by drug absorption,
✓ The speed of onset is so rapid as with IV administration that while systemic effect requires the drug to be absorbed and
cardiovascular responses may occur to drugs, which normally distributed to its site of action. Exceptions are those drugs,
have minimal effects on this system after having been absorbed and distributed, concentrate
✓ In food animals, discoloration of the meat or abscess at some local sites where they exert their action.

formation may occur to IM injection and these may be o Example: Griseofulvin, an antifungal, which when

expected to devalue the carcass. administered orally, absorbed from the gut, and distributed
to growing nails and hair produce local antifungal effect at
The rate of drug absorption from SQ site can be manipulated these sites.

to some degree of application of: • To bring about a systemic effect a drug should be

✓ Heat - increase in rate of absorption administered either enterally or parenterally and must be
absorbed.
 • When a local effect is desired, a drug is applied on ✓ stability (provides a long shelf life)
the site where the effect is wanted. ✓ niformity with respect to a drug content
Route of Administration: Time until Effect
Intravenous: 30-60 seconds The different types of solid forms are as follows:
Intraosseous: 30-60 seconds i. Powder – It is the simplest solid oral dosage form, which
Endotracheal: 2-3 minutes employed by adding the powder to drinking water or feeds. It
Inhalation: 2-3 minutes is described as finely ground drug or drugs, which some used
Sublingual: 3-5 minutes internally, while others externally.
Intramuscular: 10-20 minutes ii. Tablet – the most employed oral dosage form. It consists of
Subcutaneous: 15-30 minutes an active drug combined with a binder and excipients. It is
Rectal: 5-30 minutes described as a powdered drug compressed into a hard-small
Ingestion: 30-90 minutes disk; some are readily broken along a scored line; others are
Transdermal (topical): variable (minutes to hours) enteric coated to prevent them from dissolving in the stomach.
iii. Pills - consist of a mixture of drugs and a sticky binder that
The Different Drug Preparations has been rolled into a uniform cylinder and cut to form ovoid
Each pharmaceutical preparation is unique in its masses, which are then provided with a glazed sugar coating.
physical and pharmaceutical characteristics as well as the final iv. Capsule - hardened container made up of a mixture of
form in which the drug is presented for patient acceptance. gelatin and glycerin suitable for drug in powdered forms and
Dosage forms are preparation of drugs compounded in such a certain liquid drug.
manner as to provide a convenient means for administering a Advantages
drug dose to the patients. However, drug substances are ✓ Drugs with very unpalatable taste does not contact the oral
seldom administered in their natural or pure state.
mucosa prior to swallowing
Pharmaceutical industry combines the active ingredient
Disadvantage
(synthesized or extracted from its source) with nonmedicinal
✓ Dose cannot be fractionalized for smaller animals
agents (EXCIPENTS/PHARMACEUTICAL INGREDIENTS/AIDES/
v. Bolus – describe as large, compressed tablets, rectangular in
NECESSITIES).
shape. Used for horses and cattle to provide the larger amount
The role of excipients is to solubilize, stabilize, preserve, color,
of drug required in the dose form to a dimension that cannot
flavor, suspend, thicken, dilute, emulsify, and produce
be easily swallowed.
efficacious and appealing dosage forms.
vi. Suppositories - intended for rectal, urethral, or vaginal use.
It is made of medicinal substances incorporated in a base
Factors that Determine Drug Dosage
glycinerated gelatin which melt at body temperature.
i. Body size
vii. Lozengens - Oolong, circular, or rectangular medicated
ii. Alimentary anatomy
candies composed of the active substance, sugar, and
iii. Species variation
mucilage, which are air dried. This is intended for mouth and
iv. Genetic factor
throat medication.
v. Bioavailability
vi. Age
B. Liquid Preparation for Oral Administration
vii. Resistance
a. Mixture - aqueous solution or suspension intended for oral
viii. Sex
administration
ix. Pathology
b. Syrup - dense sugar solution in water containing medicinal
x. Timing
substance (solution of medicinal agents, flavoring,
xi. Tolerance
coloring agent in an 85% sucrose solution)
c. Elixir - hydro-alcoholic solution of medicinal substance that
A. Solid Dosage Form – the most common medical preparation
have been sweetened and flavored. It is characterized by
for oral administration
pleasant taste and stability and capable of masking bitter taste
Advantages
which is usually contained 25% alcohol.
✓ ease of administration
d. Emulsion - suspension of minute globules of oily drugs
permanently dispersed in aqueous medium, usually
containing flavoring.
e. Gargles - watery solution of a medicament, which may or
may not be flavored and is used for rinsing the mouth
and throat.
f. Extraction – either INFUSION (warm or cold water is used) or
DECOCTION (boiling water is used)

C. Dosage Form for Parenteral Administration

- The commonest stable aqueous solution
- Less frequency, active component is dissolved in an inert
vegetable oil which delays the absorption of the drug
- Drug is administered to bring systemic or local effects
- Characteristics:
• Preparation of drugs must be sterile and free of pyrogen
• Site of injection must be clean and disinfected with alcohol
to reduce chances of introducing infectious
agents into the body.
• Needles and syringes should be properly sterilized
• Drugs preparation designed for injection are frequently
adjusted to the body tonicity and pH

D. External Dosage Form

- Applied on the surface of the skin
- Local or topical administration of drugs which produces local
effects
- Systemic effect may occur due either by licking of the applied
medication or by cutaneous drug absorption
- The types are as follow:
a. Liniment or braces - liquid or semi-solid preparation applied
to the skin with rubbing. It contains counter
irritants to relieve muscles and tendon pains.
b. Lotion – a solution of suspension of soothing substances to
be applied without friction.
c. Ointment – a semisolid greasy preparation in which a drug
is dissolved in suitable base. Left in consistency
and intended for rubbing.
d. Cream - incorporate a drug in a water oil emulsion where
water will evaporate following application, leaving
the drug and a thin film of oil in the skin.
e. Dusting Powder - mixture of drug in powder form for
application to external surfaces.
f. Topical Insecticides and Wound Dressing - frequently
prepared for aerosol.