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.
A very small dosage can result in the desired therapeutic effect.
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.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is C
Explanation
Choice A rationale:
Erythromycin Erythromycin is a macrolide antibiotic that is often used as an alternative to penicillin. It is generally safe for use in patients with a penicillin allergy. It works by inhibiting bacterial protein synthesis and is effective against a wide range of bacteria.
Choice B rationale:
Amphotericin B Amphotericin B is an antifungal medication, not an antibiotic. It is used to treat serious, systemic fungal infections. It has no cross-reactivity with penicillin, so it would not be a concern for a patient with a penicillin allergy.
Choice C rationale:
Amoxicillin-clavulanate Amoxicillin-clavulanate is a type of penicillin antibiotic. Patients with a known penicillin allergy should avoid this medication, as they may have a cross-reactivity to it. This is why the nurse should verify this prescription with the provider.
Choice D rationale:
Gentamicin Gentamicin is an aminoglycoside antibiotic used to treat serious bacterial infections caused by gram-negative bacteria. It is not related to penicillin and would be safe for a patient with a penicillin allergy.
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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