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 ["A","C","D","E"]

Explanation

Choice A rationale:

Shortness of breath is a common symptom of a hypersensitivity reaction. This occurs because the body’s immune system responds to a foreign substance, known as an antigen, by producing specific antibodies. This immune response can cause inflammation and swelling in various parts of the body, including the airways, leading to shortness of breath.

Choice B rationale:

A black hairy tongue is not typically associated with a hypersensitivity reaction. It is a condition that causes the tongue to appear black and hairy, and it’s usually caused by an overgrowth of bacteria or yeast on the tongue. It’s not related to allergies or hypersensitivity reactions.

Choice C rationale:

Itching is another common symptom of a hypersensitivity reaction. When the body encounters an antigen, it triggers an immune response that releases chemicals like histamine. Histamine can cause itching, among other symptoms.

Choice D rationale:

Swelling of the tongue can be a symptom of a severe hypersensitivity reaction known as anaphylaxis. This is a medical emergency that requires immediate attention. The swelling is caused by inflammation in response to an antigen.

Choice E rationale:

Wheezing is a symptom of a hypersensitivity reaction, specifically type I hypersensitivity. This type of reaction includes allergic disorders, which affect the lungs among other parts of the body. The immune response to an antigen can cause the airways to narrow and produce a wheezing sound.

A. “The intravenous medication will have delayed absorption into the body’s tissues.” B. “The action of the medication will begin sooner when given intravenously.” C. “The medication will cause fewer adverse effects when given intravenously.” D. “There is a lower chance of allergic reactions when drugs are given intravenously.”

Correct Answer is B

Explanation

Choice A rationale:

The statement “The intravenous medication will have delayed absorption into the body’s tissues” is incorrect. Intravenous (IV) therapy is administering fluids directly into a vein. It benefits treatment by enabling water, medication, blood, or nutrients to access the body faster through the circulatory system. This bypasses the gastric system so the body can take on more fluids quickly. Therefore, the absorption of intravenous medication into the body’s tissues is not delayed but rather immediate.

Choice B rationale:

The statement “The action of the medication will begin sooner when given intravenously” is correct. Administering a medication intravenously eliminates the process of drug absorption and breakdown by directly depositing it into the blood. This results in the immediate elevation of serum levels and high concentration in vital organs, such as the heart, brain, and kidneys. Therefore, the action of the medication begins sooner when given intravenously.

Choice C rationale:

The statement “The medication will cause fewer adverse effects when given intravenously” is not necessarily true. While some medications might cause fewer adverse effects when given intravenously, this is not a general rule for all medications. The adverse effects of a medication depend on various factors including the type of medication, the dose, the patient’s health condition, and more.

Choice D rationale:

The statement “There is a lower chance of allergic reactions when drugs are given intravenously” is not necessarily true. The chance of allergic reactions depends on various factors including the type of drug, the patient’s immune response, previous exposure to the drug, and more. It’s not related to the route of administration.

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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

During antibiotic therapy, the nurse will monitor closely for signs and symptoms of a hypersensitivity reaction. Which of these assessment findings may be an indication of a hypersensitivity reaction? (Select all that apply.)

Correct Answer is ["A","C","D","E"]

Explanation

When given an intravenous medication, the patient asks the nurse, “I usually take pills. Why does this medication have to be given in the arm?” What is the nurse’s best response?

Correct Answer is B

Explanation

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