Pharmacologic Principles Jan Bazner-Chandler RN, MSN, CNS, CPNP Chapter 2
Pharmacology • The study or science of drugs • Knowledge of pharmacology allows nurse to understand how drugs affects humans.
Naming the drugs • Chemical name • Generic name • Trade name
Chemical name • Chemical composition and molecular structure
Generic Name • Shorter and simpler than the chemical name
Trade Name • Drugs registered trade mark
Generic and Trade Name • Generic name: acetaminophen • Less expensive – chemically similar to trade name drugs • Trade name: Tylenol, Tempra, Datril • More expensive
Pharmaceutics • How dosage forms influence the way in which the body metabolizes a drug and the way the drug affects the body.
Dosage Forms • A variety of dosage forms exist to provide both accurate and convenient drug delivery systems. • These delivery systems are designed to achieve a desired therapeutic response with minimal adverse effects.
Dosage Forms • Enteral: taken by mouth or PO • Parenteral: intramuscular or intravenous • Topical: applied to the skin, a patch, suppositories (rectal or vaginal)
Dosage Form • Parenteral • Injections • Solutions • Suspensions • Emulsions • Powders for reconstruction • Sublingual or buccal
Chewable Tablets • Can be chewed • Used for children • Used in the client that has a hard time swallowing pills • Break down of the drug starts in the mouth
Tablets • Are made to be swallowed whole • Are often scored so a half-dose can be give
Capsules • To be swallowed whole • Often are sustained release – 12 or 24 dosing
Enteric coated • Tablets are coated so that they do not break down in the stomach • Absorption of the drug takes place in the small intestine. • Cannot be divided into smaller doses
Sublingual • The tablet is put under the tongue • Medication is absorbed through the buccal mucosa. • Used in drug like nitroglycerine used to reduce chest pain.
Intramuscular or subcutaneous • IM or the “shot” – injected into the deep muscle of buttocks, thigh or upper arm • Antibiotics • Pain medications • Subcutaneous – injected into the fat layer just below the skin • Insulin • Anticoagulation meds: Heparin of Lovenox
Intravenous or IV • Medication is administered right into the vein. • Medications is readily absorbed right into the circulation. • Antibiotics • Regular insulin only • Pain medications • Anti-nausea or anti-emetics • Chemotherapy
Local Administration • Adhesive patches • pain control • nitroglycerine patches • Hormones • birth control patches • nicotine patches
Topical Applications • Sunscreen • Antibiotic ointments • Cortisone
Eye, Ear and Nose Drops Drops written as gtts
Rectal Suppositories • Excellent route of administration of medications for the client that is: • Vomiting / nausea • Refuses to take medication PO • Difficulty swallowing a medication • Infants – fever or pain medications
Pharmacodynamics • The mechanism by which specific drugs produce biochemical and physiologic changes in the body.
Pharmacokinetics • Movement of drugs across body membranes to reach the target organ. • 4 ways drugs move throughout the body: • Absorption • Distribution • Metabolism • Excretion
Absorption • Process that occurs from the time the drug enters the body to the time it enters the bloodstream to be circulated. • Onset of drug action is largely determined by the rate of absorption.
Absorption • Think of how the drug gets into the circulatory system and the dosage needed to bring the blood levels up to therapeutic levels. • Dosage • Interval of administration • Route of administration
Oral Drugs or PO Drugs • Dosage is determined by how much of the drug is required to be taken by mouth to given the desired affect. • Bioavailability – portion of the drug that reaches the systemic circulation.
First-pass • If a drug is metabolized by the liver before it reaches the systemic circulation, some of the active drug will be inactivated or diverted before it can reach the general circulation. • Most drugs administered by mouth have less than 100% bioavailability. • Drugs administered by the intravenous route have 100% bioavailability.
Critical thinking question • What are the effects on bioavailability in: • The infant that has an immature liver. • The geriatric patient with a poor functioning liver • The client with liver disease.
Where does absorption happen? • Very few drugs actually absorbed in the stomach (alcohol) • Small intestine • large surface area for absorption of nutrients and minerals • most drugs absorbed in small intestine
Degree and Rate of Absorption • Depends on • Route • Age and physical condition of client • Lipid or water solubility of drug • Potential drug interactions with other drugs
What else might influence oral drug absorption? • Food in stomach • Certain juices – grapefruit juice • Milk – binds with molecules of some drugs so that the drug is never absorbed • Orange juice – enhances absorption of iron taken orally • The coating on the tablet: chewable, enteric coated, slow release capsules
Distribution • Transportation of drug molecules within the body after the drug is absorbed into the blood stream.
Distribution • Drug needs to be carried to the site of the action. • Carried by the blood and tissue fluids to the sites of pharmacological action. • Distribution depends on adequacy of blood circulation.
Key Concepts of Distribution • Protein binding – drug molecules need to get from the blood plasma into the cell. • Protein binding allows part of the drug to be stored and released as needed. • Some of the drug is stored in muscle, fat and other body tissues and is gradually released into the plasma.
Just how does the drug get into the cell? • Drug must pass though the capillary wall • Blood brain barrier – very effective in keeping drugs from getting into the central nervous system or CNS – limits movement of drug molecules into brain tissue
Metabolism • Method by which the drugs are inactivated or biotransformed by the body. • Most drugs metabolized in the liver by cytochrome P450 (CYP) enzyme. • Hepatic drug metabolism or is major mechanism for terminating drug action and eliminating drugs from the body.
What can stop this process? • Enzyme inhibition • Other drugs • Combination drugs • Liver disease • Impaired blood circulation in person with heart disease • Infant with immature livers • Malnourished people or those on low-protein diets
An important concept! • First-pass effect – some drugs are extensively metabolized or broken down in the liver and only a part of the drug is released into the systemic circulation • This is why dosage is important – how much drug needs to be taken in to give the desired effect and how often does it need to be taken