Introduction of Veterinary pharmacology Somaliland Dr.Osman Abdulahi Farah

Gollis University Faculty of Agriculture and Veterinary

Medicine

Introduction to Veterinary Pharmacology

LECTURER: Dr.Osman Abdulahi FarahDate: 24 th nov 2014

IntroductionPharmacology can be defined as the study of

substances that interact with living systems through chemical process, by binding to regulatory molecules activity or inhibiting normal body process.

applications may be considered the proper role of Veterinary pharmacology, which is often defined as the science of substances used to prevent, diagnose, and treat disease for live animals.

Toxicology is that branch of pharmacology which deals with the undesirable effects of chemicals on living systems, from individual cells to complex ecosystems.

introduction

Veterinary Pharmacology is divided into two main subdivisions, pharmacokinetics and

1. pharmacodynamics . 2.Pharmacodynamics is the study of the

actions of drug on target organs. nd way of thinking about it is that

pharmacodynamics (PD)is what the drug does to the body,

Vet Pharmacokinetics(PK)

Vet Pharmacokinetics is What the body does to drug Modern pharmacology is focused on the

biochemical and molecular mechanisms by which drugs produce their physiologic effects and with the dose-response relationship , defined as the relationship between the concentration of a drug in a tissue and the magnitude of the tissue’s response to that drug.

continue

Most Vet drugs produce their effects by binding to protein receptors in target tissues, a process that activates a flow of events known as signal transduction .

Vet Drug Nomenclature

Example 1: the chemical name 2-methyl-5-nitroimidazole-l-ethanol is metronidazole. The word methylnitro is condensed to metro and ni-dazole is due to its imidazole ring

Example 2: Metoclopramide is the condensed form of the word methoxychloroprocainamide: where Me is retained and th is written as t; chloro is written as clo: and procainamide is written as pramide

Chemical name represents the exact description of the drug’s chemical composition

Generic nameGeneric name

Name that was established when drug was first manufacturedWritten in lowercase letters

Official name of a drugEach drug has only one generic nameOriginal manufacturer is only company

that can use generic name for the first 17 years

continue Brand or trade name is developed by the company

requesting approval for the drug and identifies it as the exclusive property of that company. Is Name under which the drug is sold by a specific

manufacturer Spelling always begins with a capital letter

Name is owned by the drug company and no other company may use that name

Example 1: Metrogyl® is the trade name for metronidazole. Example 2: Reglan® is the trade name for Metoclopramide. Example 3: Amoxil® is the trade name for amoxycillin. Example 4: Celebrex® is the trade name for Celecoxib

Pharmacokinetics is the description of the time course of a drug in the body, encompassing Absorption, Distribution, Metabolism, and excretion/Elimination. ADME

In simplest terms, it can be described as what the body does to the drug.

The relationship between these subdivisions and tissues over time, including drug absorption, distribution,

biotransformation (metabolism) , and excretion .

Absorption

It is the passage of drug from the site of administration into the circulation.

Bioavailability: is the extend to which a drug reaches its site of action or to biological fluid such as plasma from which the drug has access to its site of action

Aqueous solubility. Drugs given in solid form must dissolve in the aqueous biophase before they are absorbed. For poorly water soluble drugs (aspirin, griseofulvin) the rate of dissolution governs the rate of absorption. If a drug is given as water solution, it is absorbed faster than the same given in solid form or as a oily solution

continue Concentration. Passive transport depends

on the concentration gradient. A drug given as concentrated solution is absorbed faster than dilute solution.

Area of absorbing surface. If the area is larger, the absorption is faster

Route of administration affects drug absorption, because each route has its own custom

Continue Oral application. Unionized lipid soluble

drugs (e.g.ethanol) are readily absorbed from GIT. Acid drugs (aspirin, barbiturates, etc.) are predominantly unionized in the acid gastric juice and are absorbed from the stomach. Acid

drugs absorption from the stomach is slower, because the mucosa is thick, covered with mucus and the surface is small

Factors affect drug absorption

1.dose , concentration of rate administration

2. Dosage form3. Physical and chemical properties4. Route of administration

Distribution

Distribution: is the passage of a drug from the circulation

to the tissue and the site of its action. The extent of distribution of a drug

depends on its lipid solubility, ionization at physiological pH (dependent on pK), extent of binding to plasma and tissue proteins, and differences in regional blood.

flow, disease like CHF, uremia, cirrhosis. Movement of a drug proceeds until an equilibration is established between unbound drug in plasma and tissue fluids

Body fluid compartments The total body water as a percentage of

body mass varies from 50% to 70%, being rather less in women than in man.

Body water is distributed into the following main compartments

Metabolism(Biotransformation)

Metabolism includes chemical alteration of the drugs in the body. Most hydrophilic drugs (amikacin, gentamycin, neostigmine, mannitol) are not biotransformated and are excreted unchanged. The mechanism to metabolize drugs is developed to protect the body from toxins. The primary site for drug metabolism is the liver, other sites are the kidney, intestine, lungs, and plasma

Biotransformation reactions can be classified into two phases: I (no synthetic) and II (synthetic, conjugation).

Excretion

Excretion is the passage out of systematically absorbed drugs. Vet Drugs and their metabolites are excreted in: urine (through the kidney)• bile and faeces• exhaled air• saliva and sweat,milk and skin

kidney The kidney is responsible for excreting all water soluble

substances. Glomerular filtration. Glomerular capillaries have large pores.

All nonprotein bound drugs (lipid soluble or insoluble) presented to the glomerulus are filtrated. Glomerular filtration of drugs depends on their plasma protein binding and renal blood flow. Glomerular filtration rate (g.f.r.) declines progressively after the age of 50 and is low in renal failure.

Tubular reabsorption. Lipid soluble drugs filtrated at the glomerulus back diffuse in the tubules because 99% of glomerular filtrate is reabsorbed, but nonlipid soluble and highly ionized drugs are unable to do so.

continue The effect of changes in urinary pH on drug excretion is greatest for a drug having pK values between 5 to 8, because only in this case pH dependent passive reabsorption is significant. Tubular secretion is the active transfer of organic acid and

bases by two separate nonspecific mechanisms, which operate in the proximal tubules:

• Organic acid transport for penicillins,, methotrexate, drug glucuronides, etc.

• Organic base transport for thiazides, quinine, procainamide, cimetidine, amiloride, etc.

Pharmacodynamics

Vet Pharmacodynamics is the study of the biochemical and physiological effects of drugs, in certain period.

In brief, it can be described as what the drug does to the body.Drug receptorsEffects of drugResponses to drugsToxicity and adverse effects of drugs

Drug Receptor Interactions

The Lock and Key Model of Signal-Receptor Interaction

Ligands such as hormones or neurotransmitters (the"key") affect target cells by binding to specific receptors (the "lock”), which are often located in the cell membrane of animal body

This binding "unlocks" the cell's response, so that the hormone or neurotransmitter can exert its effects

Agonist

“A chemical messenger that binds to a receptor and triggers the cell’s response; often refers to a drug that mimics a normal messenger’s action”. For example, pilocarpine is a muscarinic receptor agonist

because it can bind to and activate muscarinic receptors

Drug Receptors Receptor/Binding site

“A specific protein in either the plasma membrane or interior of a target cell with which a ligand/drug combines” It must be selective in choosing ligands/drugs

to bind To avoid constant activation of the receptor by promiscuous binding of many different ligands (drugs)

It must change its function upon binding in such a way that the function of the biologic system (cell, tissue, etc) is altered This is necessary for the ligand (drug) to cause a pharmacologic effect

Antagonist is "A molecule that competes for a receptor with a chemical messenger normally present in the body. The antagonist binds to the receptor but does not trigger the cell’s response” For Example, atropine is a muscarinic receptor antagonist

because it can bind to muscarinic receptors but it does not trigger the cell’s response. In this way, it prevents binding of acetylcholine (ACh) and similar agonist drugs to the ACh recept

Any drug will be toxic once they are overdosed. toxic dose; lethal dose

Drug Receptor Interactions

Agonist Receptor

Agonist-Receptor

Interaction

Lock and key mechanism

Receptor “A specific protein in either the plasma membrane or interior of a target cell with which a chemical messenger/drug combines”

Terminology of Pharmacology, Drug

“Any substance that brings about a change in biologic function through its chemical actions”a

Dose

“The amount of a drug to be administered at one time” Duration

“The time a drug concentration is sufficient to elicit a therapeutic response

Mechanism of Action “The ways by which drugs can produce therapeutic effects”

continue Effects (therapeutic effect)

“The desired results of administration of a medication”

Side Effects (adverse effects)

“Effects that are harmful and undesired, and that occur in addition to the desired therapeutic effects”

Indications

“The reasons for administering a medication or performing a treatment”

Contra-indications

“Factor that prevents the use of a medication or treatment ( e.g., Allergies)”

continue Onset

“The time it takes for the drug to elicit a therapeutic response

Bioavailability: is the extend to which a drug reaches its site of action

Pharmacotherapeutics is the medical science concerned with

the use of drugs in the treatment of disease. Pharmacognosy is the study of drugs isolated from

natural sources, including plants, microbes, animal tissues