Understanding Pharmacodynamics and Pharmacokinetics

About this course

Drugs are used to prevent, cure, or control various diseases. To achieve this goal, adequate concentrations of the drug must be delivered to the target tissues so that therapeutic levels are obtained. Pharmacological and toxicological actions of drugs are mainly related to their plasma concentrations. Consequently, healthcare professionals who administer drugs must recognize the onset of a drug’s action as well as the intensity and duration of its effect. In turn, these are controlled by four fundamental pathways of drug movement and modification in the body, namely absorption, distribution, metabolism, and excretion. This learning content provides an overview of pharmacodynamics and pharmacokinetics through identification of common definitions and terminology and provides a brief overview of effects of a drug in single versus two compartment model administration.

Learning objectives

• Define absorption, distribution, metabolism, and excretion.
• Identify and differentiate between pharmacokinetics and pharmacodynamics
• Describe the dosage response curves
• Identify the importance of half-life and clearance of a drug
• Recall the P450 metabolic pathway

Course outline

26 sections · finish in any order across devices

1. 1

   Definitions

   Affinity

   5 min

2. 2

   Pharmacodynamics

   Pharmacodynamics is the study of how drugs effect the body. ² The most common mechanism is through the interaction of a drug with tissue receptors that are either in cell membranes or in the intracellular fluid. The extent of receptor activation and the subsequent biological response is related to t

   4 min

3. 3

   Drug Receptors

   A receptor is a single protein that a drug can attach itself to. ² There are a variety of receptor types that have been isolated and investigated, including opioid, acetylcholine, histamine-subtypes, benzodiazepines, GABA, nicotinic, muscarinic, the pain related capsaicin receptor, and countless oth

   4 min

4. 4

   Receptor Classifications

   Cell Surface Receptors

   4 min

5. 5

   Receptor Theory

   Receptors are proteins that are bound, partially bound, or unbound by a ligand (drug). When the receptor is bound to the agonist ligand (a drug that activates the receptor), the effect of the drug is produced. ⁵ The magnitude of the drug’s effect is reflective of the total number of receptors that a

   4 min

6. 6

   Drug Response Equation

   The drug response equation is fundamental to understanding pharmacology. It comes from the law of mass action and exemplifies how a drug (D) combines to a receptor (R) to form a drug receptor complex (DRC) that results in a tissue response (TR). The equation is as follows: ²˒⁴

   4 min

7. 7

   Desensitization

   Desensitization describes the occurrence of the diminished physiological response to a drug when it is administered continuously or repeatedly. The physiologic response may be increased by increasing the drug dosage or concentration, however in some cases, increasing the dosage or concentration will

   4 min

8. 8

   Drug Response Curves

   The administration of a drug is mainly determined by a mean therapeutic dose per kilogram of body weight or body surface area that is calculated from a previously determined dose for the average population. Unfortunately, this method may be responsible for the overdosing or underdosing of patients b

   4 min

9. 9

   Graded Dose Response Curve

   The graded dose response curve characterizes the changes of a drug’s concentration in a measured response when a dose of intravenous drug is increased.² The curve has a hyperbolic shape and exemplifies the greatest change in drug concentration response that occurs to the left on a small portion of t

   4 min

10. 10

    Quantal Dose Response Curve

    The quantal dose response curve provides information on the frequency with which an administered drug dose produces a desired response to similar individuals within a population and describes how there are variations in responses to a drug when administered at a threshold dose.² For example, when ad

    4 min

11. 11

    Drug Receptor Interactions

    A desired tissue response is achieved when enough free receptors are occupied and activated by a free drug. This idea holds true that at steady state, equilibrium exists between bound and unbound drug receptors and the concentration of free unbound drug at the receptor site. Key terms for receptor i

    4 min

12. 12

    Pharmacokinetics

    Pharmacokinetics describes the study of the changes in the concentration of an administered drug that occurs during absorption, distribution, metabolism, and elimination. ² This description is important, because the pharmacokinetics of a drug influences onset, duration of action, and offset of a dru

    4 min

13. 13

    Molecular Size

    A drug is better able to cross the lipid barrier and tissue membranes when it is small. When a drug is administered, it will be absorbed across a biologic membrane with small pores or openings. ³ A molecular weight greater than 200 generally is incapable of crossings membrane. Molecules can be trans

    4 min

14. 14

    Lipid Solubility and Degree of Ionization

    Most drugs are either weak acids or weak bases, and when administered they behave as a chemical in a solution in ionized and nonionized forms. ²˒⁴ The ionized form (charged form) is water soluble, and the nonionized form (uncharged form) is lipophilic. The lipophilic molecules are lipid soluble, and

    4 min

15. 15

    Protein binding

    Changes in protein binding can influence a drugs clinical effect. The number of binding sites on a plasma protein for a drug is infinite. ⁵ Binding can be overcome by adding more drugs. When the plasma concentration of a drug is reduced, or when a second drug is administered that binds with the same

    4 min

16. 16

    Absorption

    The route that a drug is administered will determine how much of the drug will be delivered to systemic circulation. When the full amount of a drug that is administer is delivered to systemic circulation, it is described as having 100% bioavailability. ²This most often occurs with intravenous admini

    4 min

17. 17

    Bioavailability

    Bioavailability describes how much of a drug reaches the effect site after it enters the circulatory system. ⁵ A drugs rate of systemic absorption will determine the intensity and duration of action that it exhibits. Various drug routes and approximate bioavailability are as follows:

    4 min

18. 18

    Compartment Models

    Compartment models exhibit the body as distinct sections with calculated volumes. Compartment models are useful in predicting changes in drug concentrations and serum concentrations in tissues. ²

    4 min

19. 19

    Plasma Concentration Curve

    The plasma concentration curve represents the decline of the plasma concentration of a drug after rapid intravenous administration. ² The y axis of the graph represents the plasma concentration. The x axis of the graph represents the amount of time after an intravenous drug is administered. The a ax

    4 min

20. 20

    Steady State

    Steady state occurs when a stable plasma concentration of a drug occurs. ¹ This results from the equilibration that occurs from continuous drug administration. Concentrations of a drug may vary between organs, but the concentrations within each of the organs does not change. This is a result of the

    4 min

21. 21

    Metabolism

    Metabolism is the enzyme-catalyzed structural change of a drug that usually occurs with more than one pathway.² The main organ for metabolism of a drug is the liver, however metabolism can also occur in the kidneys, gastrointestinal tract, plasma, heart, brain, lungs, and skin. The goal of metabolis

    4 min

22. 22

    Elimination Half-Life

    Elimination half-life is the time needed for the plasm concentration of a drug to decrease by half after a rapid bolus administration. ¹A drug is considered as being fully eliminated when approximately 95% of it has been eliminated from the body. This usually occurs within five half-lives. This is i

    4 min

23. 23

    Clearance

    The clearance of a drug is controlled by the properties of a drug and the body’s ability to eliminate it.³˒⁵ Clearance is defined as the volume of plasma that is cleared of a drug by metabolism and excretion per unit of time (Clearance=QxE). Clearance is an important concept because it influences th

    4 min

24. 24

    Conclusion

    Knowledge and competency in pharmacodynamics and pharmacokinetics are essential when administering drugs. The absorption, distribution, metabolism, and excretion of a drug is influenced by many factors, such as a drug’s lipid solubility, molecular size, surface area for absorption, hepatic and renal

    4 min

25. 25

    Pharmacodynamics and Pharmacokinetics Posttest

    Clearance is defined as the volume of plasma that is cleared of a drug by metabolism and excretion per unit of time (Clearance=QxE).

    5 min

26. 26

    Pharmacodynamics and Pharmacokinetics Posttest Answers

    Clearance is defined as the volume of plasma that is cleared of a drug by metabolism and excretion per unit of time (Clearance=QxE).

    8 min

This course satisfies

Requirement summaries come from our state requirement records. Always confirm details with your board before you renew.

References and resources

• Duffus, J. H. (2016). Dose-response curve. IUPAC Standards Online. doi:10.1515/iupac.65.0417
• Nagelhout, J. J., Plaus, K., & Kaiser Permanente School of Anesthesia Sass Elisha. (2017). Nurse anesthesia. Philadelphia, MO: Saunders.
• Pharmacodynamics. (2020). doi:10.4135/9781529728545
• Willihnganz, M., Gurevitz, S. L., & Clayton, B. D. (2019). Clayton's basic pharmacology for nurses. Maryland Heights, MO: Mosby.
• Yeager, J. J., Burchum, J., & Rosenthal, L. (2015). Study guide for pharmacology for nursing care. St. Louis, MO: Elsevier Health Sciences.

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