Pharmacology · chapter 2 · Drug Administration
Pharmacokinetics and Pharmacodynamics
The 14 things this section of the textbook says that you are most likely to be asked about — quoted word for word, not retold. Then 3 practice questions with the reasoning.
Key points
Medication knowledge before administration
Before administering a medication to a client, the nurse must understand what the body does to the drug and what the drug does to the body.
Pharmacokinetics for nursing practice
Once the nurse understands pharmacokinetics, they can better understand a drug’s actions, effects, interactions with other drugs, dosing frequency, and precautions.
Absorption factors
The route of administration influences the absorption of a drug. A drug’s physical and chemical properties affect the absorption rate, as do the physical and chemical properties of the client’s body.
Respiratory absorption
Drugs administered via the respiratory tract as gases or aerosols are quickly absorbed due to the large surface area of the lungs and the very rich blood supply there.
Bioavailability by route
IV medications are immediately 100% bioavailable because there are no barriers to absorption. Oral medications, in contrast, have several barriers to absorption, such as the pH of the stomach (acidity), the length of time the oral medication spends in the stomach, blood flow to the gastrointestinal (GI) tract, or the presence of food in the stomach.
Free drug action
Only a free drug can act at its target site of action, such as receptors, or cross into other fluid compartments within the body (Grogan Preuss, 2022).
Protein binding and toxicity
If there is a decrease in the plasma protein binding, this increases the amount of free drug available. This will intensify the effects of the drug and may even lead to toxicity.
Liver disease effects
It should be noted that any client with liver disease or cirrhosis can have decreased metabolic activity, making them more susceptible to dose-related side effects if they are taking a medication metabolized through the liver.
Liver monitoring
Monitoring liver enzymes and drug-level concentrations will help ensure that drug concentrations remain therapeutic (Herman Santos, 2023).
Renal disorders and dosing
Renal disorders such as chronic kidney disease may increase a drug’s action and duration, and clients will often need to have dosage adjustments to prevent toxicity.
Aging and drug elimination
As clients age, they experience a decline in both kidney and liver function, and the nurse must be alert to the possibility that the metabolism and excretion of drugs can be affected.
Half-life and dosing
Half-life is important because it helps determine the dosing frequency of a medication.
Long half-life risk
Medications with longer half-lives may pose a greater risk for drug toxicity because of their propensity to accumulate in the body.
Narrow therapeutic monitoring
Drug monitoring is sometimes required for drugs with a narrow therapeutic window to ensure that the client’s drug level stays within a safe range.
Terms to know
- pharmacodynamics
- The term pharmacodynamics essentially means “what the drug does to the body.”
- pharmacokinetics
- The term pharmacokinetics refers to how the body processes the medicine.
- Absorption
- Absorption refers to the process of a drug traveling from the site of administration, through the body’s membranes, and into the circulating bloodstream.
- Bioavailability
- Bioavailability refers to the amount of the active drug entering the circulation and available at the site of action—or the physical ability of a drug to reach its specific target cells to have an effect on the body.
- Drug distribution
- Drug distribution refers to the movement of a drug through the body or the way that a drug is spread throughout the body.
- Biotransformation or metabolism
- Biotransformation or metabolism is the process of chemically changing a drug into a form that can be more readily eliminated from the body.
- half-life of a drug
- The half-life of a drug is the amount of time it takes for the serum concentration to reduce by 50%.
- therapeutic index
- The therapeutic index refers to the range of dosing that is both safe and effective—the amount of drug that can produce a therapeutic effect but not so much that it causes a toxic effect.
Practice questions
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A nurse needs to administer a medication when the provider wants the drug to be available in the bloodstream immediately. Which route best matches this goal?
- Rectal administration
- Oral administration with food
- Topical administration
- Intravenous administration
Answer: Intravenous administration
Intravenous medications enter the bloodstream immediately, so there are no absorption barriers. Oral, topical, and rectal routes require absorption through membranes or tissues before the drug reaches circulation.
A client with an infected diabetic foot ulcer is receiving systemic antibiotic therapy. Which factor should the nurse recognize as a reason the antibiotic may be harder to deliver effectively to the ulcer?
- Rapid absorption in the small intestine
- Inadequate blood flow to the affected area
- Increased protein binding at the receptor site
- Immediate 100% bioavailability
Answer: Inadequate blood flow to the affected area
Distribution depends partly on tissue perfusion. In an infected diabetic foot ulcer, inadequate blood flow can make it difficult for systemic antibiotics to reach the area in effective concentrations.
Before administering a medication to a client with chronic kidney disease, which action is most appropriate for the nurse?
- Focus only on liver enzymes because kidney disease does not affect drug action.
- Hold all medications because renal excretion is the only route of elimination.
- Assess available renal function tests such as BUN and serum creatinine.
- Assume the medication will have a shorter duration of action.
Answer: Assess available renal function tests such as BUN and serum creatinine.
The nurse should assess renal function tests before medication administration when available. Chronic kidney disease may increase a drug’s action and duration, so dosage adjustments may be needed to prevent toxicity.
Where every quote comes from
Section 2.2 Pharmacokinetics and Pharmacodynamics of Pharmacology for Nurses by Tina Barbour-Taylor, Leah Mueller (Sabato), Donna Paris, Dorie Weaver, OpenStax, 2024. Read the whole section free at openstax.org.
The textbook is licensed under CC BY-NC-SA 4.0. This page quotes it word for word and adds the headings, the order and the practice questions; references to the book's figures and stray spaces left by its formatting are removed. The page is shared under the same licence. Nothing here is sold.