Pharmacology General Principles: Chapter 4 & 5
Drug half-life is defined as the amount of time required for 50% of a drug to do what? Exert a response. Be absorbed by the body. Reach a therapeutic level. Be eliminated by the body.
Be eliminated by the body * In pharmacokinetics, the time required for the body to eliminate half of an administered dose of a drug, or the time it takes to reduce the blood level of a drug by 50%, is the drug's half-life (also called elimination half-life).
What should the nurse teach a patient who is prescribed enteric-coated tablets? "Do not chew or crush the tablet." "Place the tablet under the tongue." "Dissolve the tablet in water or milk." "Eat a high-fat meal before taking the medication."
"Do not chew or crush the tablet." * Enteric-coated tablets disintegrate in the alkaline medium of the small intestine. Patients should be instructed not to chew or crush enteric-coated tablets because they will then be absorbed in the acidic medium of the stomach rather than in the small intestine. An enteric-coated tablet will not dissolve if it is placed under the tongue. The tablet must not be dissolved in water or milk to prevent alteration of the time and place of absorption. The patient should not eat a high-fat meal before taking the tablet because this will cause a delay in absorption.
A patient is given an intravenous drug. What is the bioavailability of the drug in this patient? 50% 60% 100% 110%
100% * Bioavailability is the quantity of a drug available in the body after it is administered either orally or via other routes. Bioavailability of 100% is recorded when drugs are administered intravenously directly into the bloodstream. The bioavailability of atropine is 100% because it is administered intravenously. Many drugs administered by mouth go through first-pass metabolism in the liver before beginning systemic circulation. Therefore, the bioavailability of drugs taken orally is less than 100%.
A patient is taking a drug with a low therapeutic index (TI). The nurse should be aware of which factors associated with this drug? There is a high possibility that toxicity will occur. There is less possibility of developing dependence. The chances of side effects are low with this drug relative to other drugs. Patients will be less likely to develop drug tolerance when compared to other drugs.
There is a high possibility that toxicity will occur. * A low therapeutic index (TI) indicates that the difference between the therapeutically active dose and the toxic dose of a drug is small. Therefore, a drug that has a low TI has a greater likelihood of toxicity relative to other drugs. There may be a high possibility of overdose with this drug. Tolerance and dependence are not related to the TI.
The nurse reads that the half-life of the medication being administered is 12 hours. Which interpretation should guide the nurse's care of this patient? The medication will not work for the first 12 hours. This medication will be 50% eliminated in 12 hours . The patient will require two doses of the medication before there is an effect. The medication will be administered every 6 hours to maintain consistent blood levels.
This medication will be 50% eliminated in 12 hours * The half-life (T½) of a drug is the time it takes for one-half of the drug concentration to be eliminated. Metabolism and elimination affect the half-life of a drug. For example, with liver or kidney dysfunction, the half-life of the drug is prolonged; thus, less of the drug is metabolized and eliminated. When a drug is taken continually, drug accumulation may occur.
Which is included in the study of pharmacokinetics? Interactions among various drugs Adverse reactions to medications Physiologic effects of drugs on the body Distribution rates among various body systems
Distribution rates among various body systems * Pharmacokinetics involves how the drug moves through the body, including absorption, distribution, metabolism, and excretion.
The nurse administers 100 mg of a drug by mouth. After the drug moves through the hepatic system, very little active drug is left in general circulation. What concept explains this occurrence? Drug half-life First-pass effect Therapeutic range Plasma protein binding
First-pass effect * The term first-pass effect refers to the rapid hepatic inactivation of certain oral drugs. Drugs that undergo the first-pass effect often are administered parenterally. The therapeutic range is the range of drug level between the minimum effective concentration and the toxic concentration. The drug half-life is the time required for the amount of drug in the body to decrease by 50%. Plasma protein binding is involved with the transport of drugs through the bloodstream.
Why should the nurse follow safe medication administration for intravenous (IV) medications? IV administration is irreversible. The IV route results in a delayed onset of action. Control over the levels of drug in the body is unpredictable. The IV route can result in delayed absorption of the medication.
IV is irreversible * The intravenous (IV) route allows precise control over levels of drug in the blood and results in rapid onset of action. Absorption of IV medication is instantaneous and complete. Once a drug has been injected, there is no turning back; the drug is in the body and cannot be retrieved.
A patient is complaining of pain rated 10 on a scale of 1 to 10. The nurse has several choices of pain medication to administer. Assuming there are no contraindications, which would be best for the nurse to administer at this time? Transdermal patch Tylenol suppository Oral morphine sulfate Intravenous morphine sulfate
IV morphine sulfate * When a drug is administered intravenously, it does not need to be absorbed because it is placed directly into general circulation and will have an immediate effect to decrease pain. The other medications will not have an immediate effect. Pain medications that are administered by mouth, suppository, or via a transdermal route take longer to have an effect.
The drug dobutamine acts as an agonist of norepinephrine (NE) receptors. Which effect is the nurse most likely to observe in a patient receiving this medication? Sinus bradycardia Increased heart rate Reduced cardiac output Atrioventricular heart block
Increased heart rate * Dobutamine mimics the action of norepinephrine (NE) at receptors on the heart, thereby causing an increase in the heart's rate and force of contraction.
A drug administered by which route requires the most immediate evaluation of therapeutic effect? Oral Topical Intravenous Subcutaneous
Intravenous drugs are absorbed more quickly than oral, subcutaneous, or topical drugs. The bioavailability for intravenous drugs is 100% and requires the most immediate evaluation of therapeutic effect.
The nurse administers a drug with a high therapeutic index. What does this mean about the drug? It is very potent. It has low efficacy. It is probably lethal. It is relatively safe.
It's relatively safe * Therapeutic index is a measure of a drug's safety. It is the ratio between the therapeutic and lethal dose of the drug. A large or high therapeutic index indicates that the drug is relatively safe.
Which is an alternate name for biotransformation of a drug? Dilution Excretion Absorption Metabolism
Metabolism * Metabolism involves a breakdown of a product. Biotransformation is a more accurate term because some drugs are actually changed into an active form in the liver, in contrast to being broken down for excretion.
The pharmacist states that the patient's biotransformation of a drug was altered. How should the nurse interpret this statement? Dilution has affected the drug. Excretion has affected the drug. Absorption has affected the drug. Metabolism has affected the drug.
Metabolism has affected the drug. * Metabolism involves a breakdown of a product. Biotransformation is a more accurate term because some drugs are actually changed into an active form in the liver in contrast to being broken down for excretion. Biotransformation of a drug does not occur during absorption, dilution, or excretion.
Which enzyme system is responsible for the metabolism of drugs in the liver? Ptyalin Gastric lipase P450 enzymes Pancreatic lipase
P450 enzymes * Multiple enzymes are required for the hepatic metabolism of drugs. P450 enzymes are a group of enzymes present in the liver. They are microsomal enzymes, which control a variety of reactions involved in the metabolism of medications. Pancreatic lipase, gastric lipase, and ptyalin are digestive enzymes involved in the digestion of food in the gastrointestinal tract.
Which drug property is most enhanced by the presence of many different types of receptors throughout the body? Safety Potency Selectivity Convenience
Selectivity * Because each receptor regulates just a few processes, selective drug action is possible. Multiple types of receptors do not have as much effect on potency, safety, or convenience.
What instructions will the nurse give a patient in pain to reduce fluctuations in analgesic drug levels? "Take pain medication around the clock at specified intervals and doses." "Take pain medication after breakfast and dinner to reduce stomach upset." "Take pain medication when the pain level reaches 8 or 9 on a 1 to 10 scale." "Take pain medication at night before bed and avoid daytime dosing because of drowsiness."
Take pain mediation around the clock at specified intervals and doses * One technique to reduce drug level fluctuations is to take a specified dose at regular intervals. A patient who waits for the pain to peak will have to wait longer for the pain medicine to reach a plateau level of pain control. Avoiding daytime dosing because of drowsiness and avoiding stomach upset does not address the question of how to reduce fluctuations in drug levels.
Why does the nurse monitor the patient closely after administering a drug with a low therapeutic index? There is a low variability of responses to this drug. The average lethal dose of the drug is much higher than the therapeutic dose. The dose required to produce a therapeutic response in 50% of patients is low. The highest dose needed to produce a therapeutic effect is close to the lethal dose.
The highest dose needed to produce a therapeutic effect is close to the lethal dose. * A low therapeutic index indicates that the high doses needed to produce therapeutic effects in some people may be large enough to cause death. A high therapeutic index is more desirable, because the average lethal dose is higher than the therapeutic dose. Low variability of responses to a drug is not the definition of a low therapeutic index.
The nurse has administered several oral medications to a patient. Which factor will influence the absorption of these medications? The patient must remain in a supine position. One of the drugs is a Schedule III medication. The patient has developed a tolerance to one of the drugs. The patient took an antacid immediately following drug administration.
The patient took an antacid immediately following drug administration. * Antacids raise stomach pH and bind certain drugs. The pH of the stomach affects absorption of drugs dependent on the pH of the drug. Alkaline drugs are absorbed more readily in an alkaline environment, and acidic drugs are absorbed more readily in an acidic environment. Position, drug schedule, and drug tolerance will not influence absorption.
Which term refers to the ratio between a drug's therapeutic effects and toxic effects? Affinity Tolerance Cumulative effect Therapeutic index
Therapeutic index *The ratio of a drug's therapeutic benefits to its toxic effects is referred to as the drug's therapeutic index. Tolerance is a decreased responsiveness to a drug as a result of repeated drug administration.
When administering a central nervous system depressant, the nurse should closely observe for drug toxicity in which patient? A 12-year-old boy A 3-week-old neonate A 25-year-old woman A 15-month-old infant
A 3-week-old neonate * The blood-brain barrier is not fully developed at birth. As a result, newborns are much more sensitive than older children or adults to medicines that act on the brain.
The nursing student learns that not all drugs produce effects by binding to a receptor. Which drugs do not act through receptors? Antacids Analgesics Antihistamines Steroid hormones
Antacids * Antacids do not act through receptors. Antacids neutralize gastric activity by direct chemical interaction with stomach acid.
To demonstrate the concept of drug selection based on efficacy, which PRN drug does the nurse administer for a headache that the patient describes as a "mild dullness" with a pain level of 2 on a 1 to 10 scale? Aspirin Morphine sulfate Pentazocine [Talwin] Meperidine [Demerol]
Aspirin * Maximal efficacy illustrates the fact that all drugs have a maximal effect, and dosages beyond this do not increase the effect. The goal is to match the intensity of the response to the patient's needs; therefore, a drug with high maximal efficacy is not always most desirable. Demerol, Talwin, and morphine all have a higher maximal efficacy than aspirin; therefore, aspirin is the most desirable drug for a headache rated as "mild."
The nurse is administering medications to a patient with kidney disease. Which is the nurse's priority action? Hold medications if urinary output is low. Assess the patient for medication toxicity. Administer all medications via the intravenous route. Hold all drugs that are excreted by the renal system.
Assess the patient for medication toxicity * The nurse should assess for toxicity. The kidneys are responsible for the majority of drug excretion. With excretion impaired, the medication can remain in the system longer, thus increasing the chance for toxicity to develop. Because most drugs are excreted by the renal system, it would not be appropriate to hold all drugs, as some may have more benefits than risks. Decreased urinary output is not an indication that medications should be held. Medications administered via the intravenous route are still metabolized in the body.