Nursing 3703 Pharmacology in Nursing

1. Nursing 3703Pharmacology in Nursing Introduction to Drug Therapy Linda Self

2. Grouping of Drugs • Names may reflect the conditions for which they are used (e.g. antidepressants) • May reflect their chemical characteristics (benzodiazepines) • May reflect the effects on body systems (central nervous system depressants)

3. Prototype Drugs • Individual drugs that represent groups of drugs are called Prototypes • May be the first drugs of this group to be developed (e.g., penicillin for antibiotics, morphine for opioid analgesics)

4. Drug Names • Generic Name is related to the chemical name and is independent of the manufacturer (e.g., sertraline) • Trade name is designated and patented by the manufacturer (e.g., Zoloft)

5. American Drug Laws and Amendments • 1938 Food, Drug and Cosmetic Act required proof of safety, authorized factory inspections, established penalties for fraudulent claims • 1952 Durham-Humphrey Amendment designated drugs that must be prescribed by a physician and dispensed by a pharmacist (e.g., controlled substances, etc.)

6. American Drug Laws cont. • 1970 Comprehensive Drug Abuse Prevention and Control Act; Title II, Controlled Substances Act • Categorized according to potential for abuse • Regulated distribution of narcotics and other drugs of abuse • DEA charged w/enforcing the Controlled Substances Act

7. Categories of Controlled Substances • Schedule I—not approved for medical use and have high abuse potentials; LSD, heroin, peyote, ecstasy (3,4 methyenedioxy-methamphetamine) • Schedule II—used medically. High abuse potential (methadone, meperidine, cocaine, pentobarbital, Tylox)

8. Categories of Controlled Substances continued • Schedule III-less potential for abuse than I and II but may lead to psychological or physical dependence (Vicodin, Tylenol with codeine) • Schedule IV-drugs have some potential for abuse (Valium, Dalmane, Klonopin) • Schedule V-contain moderate amounts of controlled substances. An example is Lomotil (atropine and diphenoxylate)

9. Pregnancy Categories • Cat. A-studies in pregnant women failed to show risk to the fetus • Cat. B- animal studies have failed to show a risk to the fetus but there are no adequate studies in women • Cat. C-animal studies have shown an adverse effect on the fetus, no adequate human studies, benefits may outweigh risks

10. Pregnancy Categories cont. • Cat. D-positive evidence of human fetal risk • Cat. X-animal or human studies have shown fetal abnormalities or toxicity

11. Pharmacokinetics • Involves drug movement through the body to reach sites of action, metabolism, and excretion • Specific processes are absorption, distribution, metabolism and excretion

12. Pharmacokinetics-Drug Transport Pathways • Three main pathways of drug movement across cell membrances • Most common is direct penetration by lipid soluble drugs • 2nd pathway involves passage through protein channels. Gates open and close either by voltage gating or by assist of chemical substances (Na+ and K+ ions affecting some cardiac drugs)

13. Drug Transport Pathways cont. 3. 3rd is by carrier proteins that transport molecules from one side of the cell membrane to the other. An example would be oral drugs that carry hormones to their sites of action (see text for details)

14. Pharmacokinetics • Absorption-process that occurs from the time a drug enters the body to the time it enters the bloodstream to be circulated • Factors affecting absorption include: dosage form, route of administration, blood flow to the site of administration, gastrointestinal function, presence of food or other drugs • For many medications, food in the stomach slows absorption

15. Bioavailability • Is the portion of a dose that reaches the systemic circulation and is available to act on body cells • IV administration is 100% bioavailable • Subcutaneous administrations has more rapid absorption than does the oral route • Mucous membranes allow for rapid and direct absorption into the bloodstream

16. Distribution • Involves the transport of drug molecules within the body • After the drug is absorbed into the bloodstream, it is carried by the blood or tissue fluids to its sites of pharmacologic action, metabolism and excretion • Protein binding is an important factor in drug distribution

17. Distribution cont. • Drug distribution into the CNS is limited because of the blood-brain barrier • Blood-brain barrier is composed of capillaries with tight walls which limits movement of drug molecules into brain tissue • Only drugs that are lipid soluble or have a transport system can cross the blood-brain barrier and reach therapeutic concentrations in brain tissue

18. Distribution cont. • Drug distribution during pregancy and lactation is unique as most drugs cross the placenta or in the case of lactation, pass into breastmilk

19. Protein binding • Most drugs form a compound with plasma proteins, mainly albumin, which act as carriers • Only the free or unbound portion of a drug acts on body cells • As unbound drug acts on cells, the decrease in plasma drug level causes some of the bound drug to be released • Protein binding allows a part of a drug dose to be stored and released as needed

20. Metabolism • Method by which drugs are inactivated or biotransformed by the body • Some drugs yield metabolites that are also active and exert effects on the body until they are excreted (normeperidine) • Most drugs are lipid soluble which aids their passage across the cell membrane

21. Metabolism cont. • Excretion usually is by kidneys. Need to be water soluble for this to occur. Thus, one function of metabolism is to convert fat soluble medications to water soluble ones. • Hepatic drug metabolism or clearance is a major mechanism for terminating drug action and eliminating drug molecules from the body

22. Metabolism cont. • Most drugs are metabolized by the cytochrome P450 enzymes in the liver • Liver contains complex system of enzymes, three of which are key in the metabolism of medications/drugs

23. Cytochrome p450 • CYP enzymes catalyze the chemical reactions which ultimately metabolize the medications • With chronic administration (greater than 1-3 weeks), some drugs stimulate hepatocytes to produce larger amounts of drug metabolizing enzymes (inducers). Enzyme induction accelerates drug metabolism. Result is that larger doses of the drug may be need for therapeutic effects.

24. Cytochrome p450 • Enzyme inhibition may occur with concurrent administration of two or more drugs that compete for the same metabolizing enzymes (e.g., Dilantin, EES, Tagamet) • Oral meds are generally absorbed by the GI tract and carried to the liver. Drug may undergo extensive metabolism leaving little for systemic use. This is called the first pass effect.

25. Excretion • Refers to the elimination of a drug from the body • Most are excreted by the kidneys although some are excreted in the bile then the feces

26. Serum Drug Levels • Lab measurement of the amount of a drug in the blood at a particular time • Minimum effective concentration (MEC)-must be present before a drug exerts its pharmacologic action on body cells • Duration of action-time during which serum drug levels are at or above the MEC (may measure serum drug levels when the drugs have a low therapeutic index)

27. Pharmacodynamics--Receptors • Involves drug actions on target cells and the resulting alterations in cellular biochemical reactions • Most drugs chemically bind with receptors at the cellular level • Drug-receptor complex initiates physiochemical reactions that stimulate or inhibit cellular functions

28. Pharmacodynamics-receptors • Receptors vary in type, location, number and functional capacity • When drug molecules chemically bind with cell receptors, pharmacologic effects result from agonism or antagonism

29. Pharmacodynamics-receptors • Agonists-are drugs that produce effects similar to those produced by naturally occurring hormones, neurotransmitters and others. Agonists may accelerate or slow normal cellular processes depending on the type of receptor activated. • Antagonists—drugsthat inhibit cell function by occupying receptor sites. • Not all drugs act on receptors. Examples include: antacids, osmotic diuretics, chelators.

30. Variables that affect drug actions • Dosage • Route • Drug-diet interactions. Food may slow absorption or foods may actually interact with certain medications (tyramine and MAO inhibitors; tetracycline and milk products; ingestion when taking certain antihypertensive medications)

31. Variables affecting drug actions • Drug-drug interations-additive effects such as seen with sedatives and ethanol. Synergism as seen with acetaminophen and codeine. • Antidote—drug can be given to antagonize the toxic effects of another drug

32. Variables that affect drug actions • Age • Pregnancy • Body weight • Gender-hormonal effects • Pathologic conditions • Placebo response

33. Variables that affect drug actions • Genetics-hepatic drug metabolizing enzymes===acetyltransferase. Rapid acetylators may need larger than usual dosages and conversely, smaller doses if slow acetylators • Glucose-6-phosphate deficiency—develop hemolytic anemia if take antimalarials or sulfonamides • Ethnicity—ACE inhibitors in African Americans • Tolerance and cross tolerance

34. Adverse effects of drugs • CNS • GI • Hematologic-anticonvulsants • Hepatic-acetaminophen, INH • Nephrotoxicity-aminoglycosides, NSAIDS • Hypersensitivity • Drug fever-fever associated w/administration of some antimicrobials, atropine or TCAs

35. Adverse Drug Effects • Drug dependency • Idiosyncrasy • Carcinogenicity • teratogenicity

36. Toxicology—Drug Overdosage • General management • CPR • ETT • IV • Check blood sugar, drug screen, liver and kidney function • Charcoal • Narcan or possibly antidotes • May alkalinize the urine to prevent kidney damage

37. Antidotes for Selected Therapeutic Drugs • Acetaminophen-mucomyst • Digoxin-digibind • Beta blockers-Glucagon (increases myocardial contractility) • Phenothiazines-benadryl (EPS) • Coumadin-vitamin K • Heparin-protamine sulfate

38. Antidotes cont. • Benzodiazepines—flumazenil • Cholinergics-atropine • Calcium channel blockers—calcium gluconate

39. General Principles of accurate drug administration • Six Rights • Right patient • Right drug • Right dose • Right route • Right time • Right documentation

40. General Principles cont. • Follow the ‘rights’ consistently • Learn essential information about each drug • Interpret prescriber’s orders correctly • Read labels for right medication and concentration

41. Drug Administration • Minimize the use of abbreviations • Calculate dosages correctly • Measure doses accurately • Use appropriate anatomic landmarks to identify sites of IM injections-follow manufacturers recommendations • Verify client identity

42. Drug Administration *****Seek information about the client’s medical diagnoses and condition in relation to drug administration • Be especially vigilant with children to avoid errors

43. Legal Responsibilities • Nurse is legally responsible for safe and accurate administration of medications • Nurse is expected to have sufficient drug knowledge to recognize and question erroneous orders • Unit dose wrappings of oral drugs should be left in place until the nurse is in the presence of the client and ready to administer the medication

44. Medication Orders • Include the full name of the patient • Generic or trade name of the drug • The dose, the route and frequency of administration • Date, time and signature of the prescriber

45. Common abbreviations • PO • IM • IV • SL • Sub q

46. Times of Drug Administration • AC • Ad lib • bid, tid, qid • HS • PC • PRN • Stat

47. Drug Dosages • cc • g • Gr • gtt • mL • oz • Tsp • tbsp

48. Routes of Administration • Oral • Via GI tube • Parenteral-IM, IV and sub q • Topical • Rectal, ophthalmic • Otic • vaginal

49. Sites for injections • Sub q-abdomen, thighs, back and upper arms • IM-deltoid, dorsogluteal, ventrogluteal and vastus lateralis muscles • IV-antecubital, hands, arms, external jugular • Others: intradermal, intra-articular, intra-arterial and intrathecal

50. Equivalents • Metric • Apothecary • Household • (see p. 37)