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Introduction to Pharmacology

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What is Pharmacology?

• The science of pharmacology involves the action of drugs on humans and animals.

• The aim of drug therapy is to diagnose, treat, cure, or lessen the symptoms of disease.

• The study of pharmacology applies properties and knowledge of drugs, mechanism of drug action, anatomy and physiology, and pathology,

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Drug Nomenclature

• All drugs are identified by a generic name, a chemical name, and a proprietary (brand) name.

• The official name of the drug is the generic name.

• The chemical name describes the molecular structure of the drug.

• The proprietary (brand) name is assigned by the drug manufacturer.

Prozac

Fluoxetine HCl

N-Methyl-3-phenyl-propylamine

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Examples of Generic, Chemical, and Brand Names

Generic Name Chemical Name Brand Name

Fluoxetine HCl N-methyl-3-phenyl-propylamine

Prozac

Acetaminophen 4-Hydroxyacetanilide Tylenol

Ibuprofen 2-p-Isobutylphenyl-propionic acid

Motrin

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Comparison Between Brand Name Drugs and Generic Drugs

• The inventor of a new drug may apply for patent protection. If awarded, the manufacturer is given up to 20 years exclusive rights to manufacture and distribute the new drug.

• Once the drug is off the patent, other drug companies may manufacture a generic equivalent.

• Generic drugs contain the same active ingredients as the original manufacturer’s drug, in the same strength. However, generic drugs may contain different inactive ingredients, which may affect how much of the drug is available to the body.

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Comprehensive Drug Abuse Prevention and Control Act (1970)

• Also known as the Controlled Substance Act.

• The Act regulates drugs that have a history for abuse.

• Controlled Substances are placed in a “schedule” or category according to their abuse potential and effects if abused.

• The “schedules” are determined by Federal and State laws.

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Controlled Substance Schedule

Schedule Classification Examples

C-I These drugs have a high potential for abuse. No medical uses for treatment

Ecstasy, heroin, LSD, marijuana, PCP

C-II High potential for abuse. Has accepted medical use for treatment

Morphine, oxycodone, methamphetamine

C-III Less abuse potential than C-II drugs. Accepted medical use.

Anabolic Steroids,

Hydrocodone

C-IV Less abuse potential than C-III drugs. Accepted medical use.

Valium, Xanex, Darvon, Phentermine

C-V Less abuse potential than C-IV drugs. Accepted medical use.

Cough medicines with Codeine

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FDA Pregnancy Safety Classification

• Class A – known to be safe (Vitamins)

• Class B – probably safe (Penicillin, Erythromycin)

• Class C – use cautiously if benefits outweigh risks (heparin, anti-depressants)

• Class D – known to cause fetal problems. Use only if untreated maternal disease is harmful to fetus (Lithium, Phenobarbitol, Amiodorone)

• Class E – contradicted in pregnancy (Coumadin, Methotrexate)

Thalidomide Baby

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Drug Dosage Forms and Delivery Systems

• Drugs are created for delivery by mouth (oral), injection (parenteral), inhalation, or topical application to the skin or mucous membranes.

• Oral administration is safe, easy, and generally more economical than parenteral administration.

• Common oral formulations include: tablets, capsules, solutions, emulsions, syrups, suspensions, and elixirs.

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Tablets

• Tablets are solid forms containing one or more active ingredients plus binders, which allow the drug to take a shape.

• Delayed action tablets – slow the release of the drug to avoid destruction of the drug in the stomach.

• Enteric coated tablets – have an acid-resistant coating to prevent dissolving in the stomach. Release contents into small intestine.

• Sustained release (timed release) – deliver their contents over time (ex: 24 hours). Crushing may cause contents to be released immediately.

• Chewable tablets – for people who have difficulty swallowing pills. Used frequently with children.

• Sublingual tablets – dissolved in the mouth, where many blood vessels are located. Gets into bloodstream fast and by-passes stomach.

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Capsules

• Capsules are solid dosage forms containing one or more active ingredients plus binders and fillers.

• Formulated to deliver their ingredients immediately or over time.

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Oral Liquids

• Oral Liquids are easy to swallow and work more rapidly than tablets or capsules.

• Suspensions – contain small drug particles suspended in a liquid.

• Solutions – drug particles are completely dissolved in the liquid.

• Syrups – contain a high concentration of sucrose or other sugars.

• Elixirs – contain between 5% and 40% alcohol.

• Tinctures – contain between 17% and 80% alcohol.

• Emulsions – similar to suspensions. May be dispersed in oil or water.

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Topical Administration

Ointments – semisolid preparations containing petroleum or another base. Form a protective barrier between the skin and harmful substances.

Creams – semisolid emulsions applied directly onto the skin.

Suppositories – solid or semisolid dosage forms intended to be inserted into a body orifice. Melt at body temperature, dispersing the medicine

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Transdermal Drug Delivery System

Transdermal patches are controlled-released devices that deliver medication across skin membranes into the general circulation. They produce both local and systemic effects.

Examples:

Nitroglycerin for angina

Estrogen for menopause

Fentanyl for pain

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Routes of Administration of Drugs

By Mouth, Oral (PO): The major benefit of oral administration is the convenience to the patient.

-Oral medications are systemic (work throughout the body)

-Safer, because they take time to work and therefore an antidote can be given if overdosed.

-However, these drugs do not work as quickly

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Routes of Administration of Drugs

Sublingual and Buccal Agents (SL, Buccal): Few medications are administered in this form, but the medications administered in this manner are very effective. These medicines by-pass the digestive system, and are absorbed directly into the blooodstream.

-Nitroglycerin is given sublingually for Angina.

-Parcopa is given sublingually for Parkinson’s

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Routes of Administration of Drugs

Rectal Agent (PR): may be used in patients who are vomiting and cannot take oral medications. Suppositories or rectal creams may be used. These agents usually work locally, not systemically.

-Suppositories for motion sickness, nausea (systemic effects)

-Laxatives (work locally)

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Routes of Administration of Drugs

Topical Agents: topical agents can have systemic or local effects. They are popular due to the ease of application, and the rapid effect produced.

-Examples include Bacitracin (antibiotics), Benadryl (antihistamine), Estrogen patches (hormonal), some blood pressure medications, and smoking cessation agents.

-May cause skin reactions. -More expensive than oral

medications.

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Routes of Administration of Drugs

Parenteral (Intravenous, Intramuscular, Subcutaneous): given “outside the intestines”.

-Benefits: speed of action, not inactivated by stomach acids, not harmful to the stomach.

-Disadvantages: increased risk of infection, difficult to reverse toxic or allergic effects, more expensive, must be given by trained medical personnel.

-Examples: Insulin, Heparin (blood thinner), IV antibiotics, chemotherapy.

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Routes of Administration of Drugs

Inhalants: primarily used in patients with respiratory (lung) diseases. Also used to anesthetize patients prior to surgical procedures.

-Benefits: ease of use, quick onset of action

-Disadvantages: must be used properly to be effective.

-Examples: Albuterol Inhaler (Bronchodilator for Asthma), Nitrous Gas (anesthesia for dental/surgical procedures).

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Pharmacokinetics

Once a drug is administered to a patient, the drug then undergoes the 4 phases of Pharmacokinetics. These phases include:

-Drug absorption into the bloodstream

-Drug distribution to their site of action before they produce

their effects.

-Drug metabolism by the body

-Drug elimination from the body

These pharmacokinetic phases control the intensity of a drug’s effect and the duration of the drug action.

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Pharmacokinetics

The absorption of a drug is dependent upon:

-the tissue thickness

-blood flow to the area

-drug concentration

-surface area (ex: microvilli of the small intestines

-lipid solubility of the drug, allowing it to pass through the cell membrane

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Pharmacokinetics

Drug distribution is the process of movement of the drug from the circulatory system, across barrier membranes, to the site of drug action.

The quantity (volume) of drug distributed is influenced by:

-the properties of the drug -the extent of drug binding to blood

proteins -the blood supply to the region -the ability of the drug to cross natural

body barriers (ex: blood-brain barrier, blood-placenta barrier)

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PharmacokineticsMetabolism: most drugs are

transformed by enzymes (usually in the liver) to a metabolite that is less active than the original drug.

Biotransformation is the process of drug metabolism in the body that transforms a drug to a more active, equally active, or inactive metabolite.

The main site of biotransformation occurs in the liver.

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Pharmacokinetics

Factors Influencing Metabolism:

1. Liver Function: the liver is the primary site for metabolism. If the liver function decreases, metabolism decreases. In cases of liver disease, drug doses should often be reduced because less drug is capable of being broken-down by the liver.

Jaundice –notice yellow sclera

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Pharmacokinetics

Factors Influencing Metabolism:

2. Effects of Disease: Diseases like hepatitis decrease the metabolic capacity of the liver. Lung disease and Kidney disease can also reduce the body’s ability to metabolize drugs.

3. Effects of Age: Metabolism in the liver is decreased in both the elderly and in infants. Therefore, infants and the elderly require lower doses of drug to produce therapeutic effects.

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Pharmacokinetics

Factors Influencing Metabolism:

4. Interactions of two or more drugs: Administration of two or more drugs that both use the same metabolic pathways can alter the metabolism of eachother.

-Ex: Phenytoin is a drug used to treat epilepsy. Phenytoin can increase the metabolism of Warfarin, a drug used to decrease blood clotting. This will make Warfarin less effective.

-Ex: St. John’s Wart, an herb, can increase the metabolism of birth control pills, causing a woman to possibly get pregnant while “on the pill”.

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Pharmacokinetics

Elimination is the final pharmacokinetic phase. Elimination results in the removal of the drug from the body, and discontinuation of drug action.

The three major routes of drug elimination are: -kidney -lung -bowel

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PharmacokineticsElimination Half-life (T1/2) – the

time it takes for 50% of the drug to be cleared (eliminated) from the bloodstream.

It takes approximately 8 half-lives to entirely eliminate a drug from the body.

Every drug has its own unique half-life. It is important to know a drug’s half-life, because it is an indicator as to how long a drug will produce effects in the body.

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PharmacokineticsBioavailability – the extent to which an administered

amount of drug reaches the site of action and is available to produce drug effects.

Bioavailability is influenced by drug absorption and distribution to the site of action.

Bioequivalent drugs – achieve the same maximum blood concentration, in the same period of time.

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Pharmacokinetics

The area under the curve (shaded area) is the measure of a drug’s bioavailability

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Two dose forms of the same drug are depicted. These two dose forms have equal bioavailability and they are bioequivalent.

Two dose forms of the same drug are depicted. These two dose forms have equal bioavailability but they are NOT bioequivalent.

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Pharmacodynamics

Pharmacodynamics – is the study of drugs and their action on the living organism.

-looks at how the body responds to drugs that are administered.

Mechanism of Action – describes how the drug produces its effects.

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Pharmacodynamics

Drug-receptor theory – drugs interact or bind with targeted cells in the body to produce pharmacologic action.

The location of the drug-cell binding is called the receptor site.

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Pharmacodynamics

Drug-receptor binding is similar to the action of a lock and key. The drug is the key, and the receptor is the lock.

The more similar the drug is to the shape of the receptor site, the greater the affinity (attraction) that the receptor site has for the drug.

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Pharmacodynamics

Types of Drug-Receptor Interactions:

Drugs are described as agonists, partial agonists, competitive antagonists, and non-competitive antagonists based on their effect at the receptor site.

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Pharmacodynamics

Agonist – is a drug that binds to and activates the receptor site, eliciting a response.

Partial Agonist – is a drug that binds to a receptor, but produces a reduced (diminished) response, compared with that of an agonist.

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Pharmacodynamics

Antagonist – binds to the receptor site and does not produce an action. The drug prevents the binding of agonists.

Competitive Antagonist – drug competes with the agonist for the binding site of the receptor. If it binds, there is no response.

Noncompetitive Antagonist – drug binds with an alternative site on the same receptor (not at the same site as the agonist), inactivating the receptor site.

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Pharmacodynamics

Efficacy – describes the maximum response produced by a drug. It is a measure of a drug’s effectiveness.

-Agonists produce the maximum drug response.

Which drug has higher efficacy, Drug A or Drug B?

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Pharmacodynamics

Potency – Efficacy and potency are related. Drugs that have high efficacy at low dose are very potent.

-Drugs that are very potent require only a small dose to produce a maximum drug effect.

Which drug is more potent, Drug A or Drug B?