Pharmacology Introduction PDF

Pharmacology Basics Introduction to Pharmacology  Learning Objectives At the end of this chapter the student will be able to: 1. Define various terminologies used in Pharmacology 2. Understand pharmacodynamics and pharmacokinetics (absorption, distribution, metabolism and excr...

Pharmacology Basics Introduction to Pharmacology  Learning Objectives At the end of this chapter the student will be able to: 1. Define various terminologies used in Pharmacology 2. Understand pharmacodynamics and pharmacokinetics (absorption, distribution, metabolism and excretion) of drugs 3. Understand theoretical pharmacokinetics like half-life, order of kinetics, steady state and plasma concentration 4. Understand drug safety and effectiveness like factors affecting drug action and adverse drug reactions  Definitions Pharmacology: from Greek , pharmakon, "drug"; logia, "the study of“ (study of the drug) The science that deals with effects of drugs on living system. It includes the history, source, physicochemical properties, dosage forms, methods of administration, absorption, distribution, mechanism of action, biotransformation, excretion, clinical uses and adverse effects of drugs Drug `Any substance or product` that is used or intended to be used to modify physiological systems or pathological states for the benefit of the recipient. A substance used in the prevention, treatment or diagnosis of disease.  Pharmacokinetics (PK): Study of the absorption, distribution metabolism and excretion (ADME) of drugs (“ What the body does to a drug ”) Pharmacodynamics (PD): The study of the biological and therapeutic effects of drugs (“What the drug do to the body”) Pharmacotherapeutics: It deals with the proper selection and use of drugs for the prevention and treatment of disease Toxicology: Toxicology is the branch of pharmacology dealing with the "undesirable" effects of drugs on biological processes  Clinical pharmacology: Is the systematic study of a drug in humans, both in healthy volunteers and patients. It includes the evaluation of pharmacokinetic and pharmacodynamics data, safety, efficacy, and adverse effects of a drug. Pharmacy: It is the branch of science that deals with the preparation, preservation, compounding and proper use of drugs  Food & Drug Administration (FDA) The federal agency responsible for the safety and efficacy of all drugs in the US. It is also responsible for food and cosmetics. Adverse or “Side-Effect” An unintended action of a drug. Results from a lack of specificity of drug action. All drugs are capable of producing adverse effects.  Drug Names Chemical name The drug’s chemical composition and molecular structure Generic name (nonproprietary name) Name given by the United States Adopted Name Council Trade name/ Brand name/Product (proprietary name) The drug has a registered trademark; use of the name restricted by the drug’s owner (usually the manufacturer) Chemical Name Generic Name/ Brand Name/ Non- Proprietary Proprietary Name Name Isobutylphenylpr- Ibuprofen Trufen, Advil, opionc acid Ultrafen Acetaminophen Paracetamol Otamol, Acamol, Sedamol, Aminobenzyl Ampicillin Ampipharm Penicillin To avoid confusion: it’s best to use a drug’s generic name Grouping of drugs: Pharmacologic class (or family): – drugs that share similar characteristics – Example: beta-adrenergic blockers are an example of a pharmacologic class. Therapeutic class: – groups drugs by therapeutic use – Example: Antihypertensives Principles of Prescription Writing  Definition A prescription is a written, verbal, or electronic order from a practitioner or designated agent to a pharmacist for a particular medication for a specific patient.  The “Five Rights” of Medication Administration ❖ Right drug ❖ Right dose ❖ Right time ❖ Right route ❖ Right patient  Prescription Formatting Heading Body Closing  Tablets - tab Capsule – cap Syrup – syr Suspension – susp Injection – Inj Metered dose inhaler – as such Lotion – as such  PO: by mouth PR: per rectum IM: intramuscular IV: intravenous ID: intradermal IN: intranasal TP: topical SL: sublingual BUCC: buccal IP: intraperitoneal  Controlled Substances Definition - a prescription drug whose use and distribution is tightly controlled because of its abuse potential or risk Regulation is more strict Routes of Drug Administration ROUTES OF DRUG ADMINISTRATION Drug and patient related factors determine the selection of routes for drug administration 1. Properties of the drug water or lipid solubility, ionization, effect of gastric pH, digestive enzymes, first pass metabolism 2. Therapeutic objectives Onset of action/ duration of treatment (emergency/ routine use) Site of action (local / systemic). 3. Condition of the patient (unconscious, vomiting, diarrhea) 4. Age of the patient 5. Patient`s/doctor`s choice ROUTES OF DRUG ADMINISTRATION Major routes of drug administration include: A. Enteral: oral, sublingual, buccal. B. Parenteral: Intravenous (IV), Intramuscular (IM), Subcutaneous (SC), Intradermal (ID). C. Others: transdermal, nasal inhalation, oral inhalation, topical (skin cream, eye drops, ear drops), rectal, vaginal … etc 1. Oral: Most common and acceptable route Advantages: Convenient - can be self- administered, pain free, easy to take Absorption - takes place along the whole length of the GI tract Cheap - compared to most other parenteral routes Safe- low risk of infection Overdose and toxicities can be overcome by antidotes, such as charcoal 1. Oral: Disadvantages: Sometimes inefficient - only part of the drug may be absorbed ✔ Absorption can be affected by several factors, as gastric pH ✔ Destruction of drugs by gastric acid and digestive juices ✔ First-pass effect - drugs absorbed orally are initially transported to the liver via the portal vein Irritation to gastric mucosa - nausea and vomiting Effect too slow for emergencies Unpleasant taste of some drugs Unable to use in unconscious patient First-pass Effect The intestinal and hepatic degradation or alteration of a drug or substance taken by mouth. The greater the first-pass effect, the less the agent will reach the systemic circulation when the agent is administered orally 1. Oral: Wide range of oral preparations including: A. Enteric-coated preparations B. Extended- release preparations A. Enteric-coated preparations: Is a chemical envelope that resists the action of fluids and enzymes in the stomach but dissolves readily in the upper intestine. Such coat is useful for: 1. Drugs that are acid unstable (e.g. Omeprazole) 2. Stomach irritating drugs (e.g. Aspirin) B. Extended-release Preparations (ER or XR): Have special coating or ingredients that control how fast the drug is released from the pill into the body Advantages: Slower adsorption and prolonged duration Better patient compliance May maintain concentrations within acceptable therapeutic range over a long period of time These preparations are advantageous for drugs with short half lives 2. Sublingual/ Buccal: Placement under the tongue allows a drug to diffuse into the capillary network and enter the systemic circulation directly The buccal route: drug is place between cheek and gum Advantages: – Ease of administration – Rapid absorption – Low risk of infection – Bypass of the harsh GI environment – Avoid the first-pass metabolism 2. Sublingual/ Buccal: Disadvantages Inconvenient Small doses Unpleasant taste of some drugs II. Parenteral route: Introduces drugs directly across the body’s barrier defenses into systemic circulation Uses: – Drugs that are poorly absorbed from GI tract (e.g. heparin). – Drugs that are unstable in the GI tract (e.g. insulin) – In patients unable to take oral medication (e.g. unconscious patients) – Circumstances that require a rapid onset of action  Advantages: – Avoid first-pass metabolism or harsh GI environments. – provides the most control over the actual dose of drug delivered to the body. – Good bioavailability Disadvantages: – Irreversible – Low convenience, may cause pain, fear – local tissue damage, and infections. 1. Intravenous (IV): Drugs are injected directly into the blood stream through a vein Drugs are administered as: – Bolus – Slow intravenous injection – Intravenous infusion  1. Intravenous (IV): Uses and advantages: For drugs that are not absorbed orally For administering chemicals that may cause irritation when administered via other routes Control over the amount of drug delivered Absorption phase is bypassed (100% bioavailability) Precise, accurate and almost immediate onset of action large quantities can be given, fairly pain free 1. Intravenous (IV) Disadvantages: Irreversible May introduce infection at the site of injection Risk of embolism Risk of adverse reactions by the too-rapid delivery of high concentrations of a drug to the plasma and tissues 2. Intramuscular (IM): Drugs are injected into a large muscle Drugs administered IM can be: 1. Very rapid absorption of drugs in aqueous solution 2. Slow release preparations: Depot Effect Pain at injection sites for certain drugs Depot preparations: Often consist of a suspension of the drug in a non-aqueous vehicle such as polyethylene glycol Vehicle diffuses out of the muscle, the drug precipitates at the site of injection The drug then dissolves slowly, providing a sustained dose over an extended period of time 3. Subcutaneous (SC): This route provides absorption via simple diffusion Slower than the IV route Advantages of SC injection: – Minimizes the risks of hemolysis or thrombosis associated with IV injection – May provide constant, slow, and sustained effects. SC route should not be used with drugs that cause tissue irritation Absorption is limited by blood flow, affected if circulatory problems exist 4. Intradermal (ID) The intradermal (ID) route involves injection into the dermis, the more vascular layer of skin under the epidermis. Agents for diagnostic determination and desensitization are usually administered by this route III. Others 1. Oral inhalation Gaseous and volatile agents and aerosols Rapid onset of action due to rapid access to circulation a. Large surface area b. Thin membranes separates alveoli from circulation This route is particularly effective and convenient for patients with respiratory complains (such as asthma) 2. Nasal inhalation: Administration of drugs directly into the nose. Local effect: – Nasal decongestants, such as oxymetazoline – Anti inflammatory corticosteroids, such as mometasone furoate Systemic effect: Desmopressin for diabetes insipidus treatment 3. Intrathecal/intraventricular: Introduce drugs directly into cerebrospinal fluid, when: Drugs cannot cross the blood-brain barrier to the CNS Local, rapid effects are needed, it is necessary to introduce drugs directly into the cerebrospinal fluid. 4. Topical: Drug is applied to the skin or mucous membrane at various sites for local effect Mucosal membranes (eye, nasal, vaginal, rectal,,,,,.) Skin: ointment, cream,,, 4. Transdermal The drug is administered in the form of patch that deliver the drug into systemic circulation (systemic effect) I. Stable blood levels II. No first pass metabolism III. Drug must be potent or patch becomes to large IV. Variable rate of absorption 5. Rectal Advantages Unconscious patients and children If patient is nauseous or vomiting Good for drugs affecting the bowel such as laxatives Easy to terminate exposure Disadvantages: Absorption may be variable Irritating drugs contraindicated  Important Info The ROA is determined by the physical characteristics of the drug, the speed which the drug is absorbed and/ or released, as well as the need to bypass hepatic metabolism and achieve high conc. at particular sites