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

A.

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

B.

The phenytoin has a low chance of being effective.

C.

There is no difference between safe and toxic plasma levels.

D.

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

E.

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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Related Questions

Correct Answer is C

Explanation

Choice A rationale:

Administering the medications using a 3-mL medication syringe is not the best practice. While it is possible to use a 3-mL syringe for medication administration, it is not the most efficient or safest method. A larger syringe allows for easier administration and reduces the risk of creating too much pressure which could potentially damage the PEG tube.

Choice B rationale:

Applying firm pressure on the syringe’s piston to infuse the medication is not recommended. This can create too much pressure in the PEG tube and could potentially cause damage. It is generally advised to allow the medication to flow into the tube via gravity. Choice C rationale:

Flushing the tubing with 30 mL of saline after the medication has been given is the correct technique. This helps to ensure that all of the medication has been administered and also helps to keep the tube clear of any potential blockages.

Choice D rationale:

Using the barrel of the syringe, allowing the medication to flow via gravity into the tube is a common practice. However, it is not the only step in the process. It is also important to flush the tube before and after medication administration to ensure all medication is delivered and to maintain the patency of the tube.

Correct Answer is ["50 "]

Explanation

The question is about calculating the volume of phenytoin oral solution that the nurse should administer per dose. The client is prescribed 250 mg of phenytoin and the available solution has a concentration of 25 mg/5 mL.

Let’s calculate the volume step by step:

Step 1: Identify the prescribed dose and the concentration of the available medication. The prescribed dose is 250 mg and the concentration of the available medication is 25 mg/5 mL.

Step 2: Set up the calculation. We want to find out how many mL correspond to the prescribed dose. We can set up the calculation as follows: (Prescribed dose ÷ Concentration) × Volume.

Step 3: Substitute the known values into the calculation. This gives us: (250 mg ÷ 25 mg/5 mL).

Step 4: Perform the division operation first due to the order of operations (BIDMAS/BODMAS). This gives us: (250 mg ÷ 5 mg/mL).

Step 5: Perform the final calculation. This gives us: 50 mL.

So, the nurse should administer 50 mL of the phenytoin oral solution per dose.

Please note that this calculation assumes that the prescribed dose (250 mg) is to be administered in one go. If the dose is to be split over the day, the volume to be administered would change accordingly.

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