Phenytoin has a narrow therapeutic index.
The nurse recognizes that this characteristic indicates which of these?

The safe and the toxic plasma levels of the drug are very close to each other.

The phenytoin has a low chance of being effective.

There is no difference between safe and toxic plasma levels.

A very small dosage can result in the desired therapeutic effect.

Answer and Explanation

The Correct Answer is A

Choice A rationale:

Phenytoin is an anticonvulsant drug used in the prophylaxis and control of various types of seizures. It has a narrow therapeutic index, which means that the safe and toxic plasma levels of the drug are very close to each other. This characteristic makes the dosing of phenytoin challenging, as even small deviations from the recommended therapeutic range can lead to suboptimal treatment or adverse effects. Therapeutic effect without clinical signs of toxicity occurs more often with serum total concentrations between 10 and 20 mcg/mL34. Therefore, clinicians are advised to initiate therapeutic drug monitoring in patients who require phenytoin.

Choice B rationale:

The statement that phenytoin has a low chance of being effective is incorrect. Phenytoin is a widely used and effective anticonvulsant. It works by slowing down impulses in the brain that cause seizures. It is used to control seizures but does not treat all types of seizures. The effectiveness of phenytoin is not determined by its narrow therapeutic index but by its pharmacological action in the brain.

Choice C rationale:

The assertion that there is no difference between safe and toxic plasma levels of phenytoin is incorrect. There is indeed a difference between the safe (therapeutic) and toxic levels of phenytoin. The therapeutic range for phenytoin is typically between 10 and 20 mcg/mL34. Levels above this range can lead to toxicity, while levels below this range may not provide the desired therapeutic effect.

Choice D rationale:

The statement that a very small dosage of phenytoin can result in the desired therapeutic effect is not entirely accurate. While it’s true that phenytoin is effective in controlling seizures, the dosage required to achieve this effect is not necessarily “very small”. The usual adult dose for seizures is 100 mg orally 3 times a day. The dosage may need to be adjusted based on individual patient factors and response to therapy. Therefore, it’s not accurate to generalize that a “very small” dosage will result in the desired therapeutic effect for all patients.

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Correct Answer is C

Explanation

Choice A rationale:

Blood glucose levels are not typically affected by rifampin and pyrazinamide. These medications are primarily used to treat tuberculosis and do not have a direct impact on blood sugar levels.

Choice B rationale:

Thyroid function studies are not usually required when a patient is on rifampin and pyrazinamide. These medications do not typically affect the thyroid gland or its function.

Choice C rationale:

Liver function tests are crucial when a patient is on rifampin and pyrazinamide. Both of these medications can cause liver problems, including hepatitis. Therefore, regular monitoring of liver function is necessary to detect any potential damage early and adjust the treatment plan accordingly.

Choice D rationale:

Gallbladder studies are not typically required for patients on rifampin and pyrazinamide. These medications do not have a known direct impact on the gallbladder.

A. Hold the drug, and administer 4 hours later. B. Administer the vancomycin as ordered. C. Hold the drug, and notify the prescriber. D. Repeat the test to verify results.

Correct Answer is C

Explanation

Choice A rationale:

Holding the drug and administering it 4 hours later is not the appropriate action. The trough vancomycin level of 24 mcg/mL is higher than the recommended range of 10-20 mcg/mL, indicating potential risk for toxicity. Administering the drug later does not address the immediate concern of a high trough level.

Choice B rationale:

Administering the vancomycin as ordered is not the correct action in this case. The trough level is above the recommended range, which could lead to vancomycin toxicity. The nurse should not administer the medication without addressing the high trough level. Choice C rationale:

This is the correct action. The nurse should hold the drug and notify the prescriber because the trough vancomycin level is higher than the recommended range. The prescriber can then make a decision based on this information, which may include adjusting the dose, extending the dosing interval, or ordering additional tests.

Choice D rationale:

While repeating the test to verify results might be done eventually, it should not be the immediate next step. The nurse has a responsibility to ensure patient safety, and with a trough level above the recommended range, the priority is to prevent potential toxicity. Therefore, the nurse should hold the drug and notify the prescriber.

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Phenytoin has a narrow therapeutic index. The nurse recognizes that this characteristic indicates which of these?

Nursing Test Bank

Naxlex Comprehensive Predictor Exams

A nurse is caring for a client who has tuberculosis and new prescriptions for rifampin and pyrazinamide. Which of the following laboratory tests should the nurse instruct the client will be required while on this medication regimen?

Correct Answer is C

Explanation

The nurse checks the patient’s laboratory work prior to administering a dose of vancomycin and finds that the trough vancomycin level is 24 mcg/mL. What will the nurse do next?

Correct Answer is C

Explanation

A nurse is collecting data on a patient who has hyperthyroidism. Which of the following symptoms should the nurse anticipate the patient to report?

A nurse is caring for a client who has recurrent kidney stones and a history of diabetes mellitus. The client is scheduled for an intravenous Pyelogram (IVP). The nurse should collect additional data about which of the following statements made by the client?

A nurse is collecting data from a client who has diabetes mellitus. Which of the following findings indicates that the client is experiencing DKA?

A nurse is documenting an 8-hour intake and output (I&O) record for a patient who consumed 4 oz of juice, 6 oz of tea, a 100 mL cup of soda, an IV bolus of 150 mL, and 8 oz of broth. How many mL of intake should the nurse record on the patient’s chart?

A nurse is preparing to administer amoxicillin 2 gm/day PO divided into two doses. The amount available is amoxicillin 500 mg tablets. How many tablets should the nurse administer with each dose?

A nurse is preparing to administer methylnaltrexone 12 mg subcutaneously to a client who has opioid-induced constipation. The available methylnaltrexone is 8 mg/0.4 mL. How many mL should the nurse administer? (Round the answer to the nearest tenth. Use a leading zero if it applies.

Which of the following medications is typically prescribed for the treatment of hyperthyroidism?

A patient is experiencing nausea and decreased appetite during drug therapy with a tetracycline antibiotic. What is the nurse’s best advice to the patient?

Phenytoin has a narrow therapeutic index.
The nurse recognizes that this characteristic indicates which of these?