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

No explanation

A. Proton pump inhibitors B. Calcium channel blockers C. Loop diuretics D. Phenytoin

Correct Answer is C

Explanation

Choice A rationale:

Proton pump inhibitors (PPIs) are used extensively for the treatment of gastric acid-related disorders, often over the long term, which raises the potential for clinically significant drug interactions in patients receiving concomitant medications.

However, there is no specific mention of a significant interaction between PPIs and aminoglycosides.

Choice B rationale:

Aminoglycoside antibiotics and calcium channel blockers can interact at the neuromuscular junctions. This interaction is of clinical significance because when these agents are given concurrently during the perioperative period they may lead to respiratory depression or prolonged apnea. However, this is not directly related to the therapeutic effect of aminoglycosides, but rather a side effect of their combined use.

Choice C rationale:

The loop-diuretics (ethacrynic acid, furosemide, bumetamide) and aminoglycoside antibiotics (kanamycin, gentamicin, tobramycin, amikacin, etc.) are important drugs frequently used to treat seriously ill patients. Not uncommonly both types of drugs are given to the same patient exposing that patient to the risk of a hearing loss (ototoxicity)5. In addition, the risk of ototoxicity could be enhanced by the concomitant use of loop diuretics and aminoglycoside antibiotics.

Choice D rationale:

Phenytoin is a medication used to treat seizures. It has a complex pharmacokinetic profile and can interact with many other drugs. However, there is no specific mention of a significant interaction between phenytoin and aminoglycosides.

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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

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Correct Answer is C

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Correct Answer is C

Explanation

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