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

The correct answer is Choice C.

Let’s go through the calculation step by step:

Step 1: Identify the order and the available medication. The order is for dexamethasone (Decadron) 6mg IM. The available stock is dexamethasone 4mg/1ml in a 5ml multidose vial.

Step 2: Determine the amount of medication needed to fulfill the order. This is done by dividing the ordered amount by the concentration of the available medication.

So, we have:

Step 2 Calculation=Concentration of Available MedicationOrdered Amount Substituting the given values: Step 2 Calculation=4 mg/mL6 mg Step 3: Perform the calculation.

Step 3 Calculation=1.5 mL

So, the nurse will prepare 1.5 mL of this medication.

Now, let’s discuss the rationales for each choice:

Choice A rationale:

75 mLs is not the correct amount. This would be a significantly larger dose than ordered, which could lead to an overdose.

Choice B rationale:

5 mLs is not the correct amount. This would also be a larger dose than ordered, which could lead to an overdose.

Choice C rationale:

1.5 mLs is the correct amount. This is calculated by dividing the ordered dose (6 mg) by the concentration of the available medication (4 mg/mL).

Choice D rationale:

15 mLs is not the correct amount. This would be a significantly larger dose than ordered, which could lead to an overdose.

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

The physician orders an injection of dexamethasone (Decadron) 6mg IM for a patient. The available stock is dexamethasone 4mg/1ml in a 5ml multidose vial. How many mLs of this medication will the nurse prepare?

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

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A nurse is caring for a client who was exposed to anthrax. Which of the following antibiotics should the nurse plan to administer?

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