A nurse is preparing to administer phenytoin 75 mg PO. Available is phenytoin suspension 25 mg/5 mL. How many mL should the nurse administer?
(Round the answer to the nearest whole number. Use a leading zero if it applies. Do not use a trailing zero.)

Step 1 is to calculate the volume of medication to administer. The formula is desired dose ÷ available dose × available volume. So, (300 mg ÷ 250 mg) × 5 mL = 6 mL.

So, the correct answer is 6 mL.

The correct answer is Choice B

Choice A rationale: Dantrolene is a direct-acting skeletal muscle relaxant that works by inhibiting calcium release from the sarcoplasmic reticulum in muscle cells, thereby reducing muscle contraction. It is not intended for as-needed use during acute spasms but requires consistent dosing to maintain therapeutic levels. Intermittent use undermines its pharmacokinetics and may lead to subtherapeutic effects. The half-life of dantrolene is approximately 8.7 hours, and steady-state levels are necessary for optimal spasticity control in multiple sclerosis.

Choice B rationale: Dantrolene’s therapeutic effect on muscle spasticity may take several weeks to manifest due to its mechanism of action involving gradual reduction in intracellular calcium availability. If no improvement is noted within 3 months, it may indicate inadequate response or the need for dosage adjustment. Monitoring for efficacy is essential, as prolonged use without benefit increases risk of hepatotoxicity. Liver function tests should be monitored regularly. Normal ALT levels are 7–56 units/L; elevations may signal toxicity.

Choice C rationale: Dantrolene is classified as pregnancy category C, indicating that risk to the fetus cannot be ruled out. Animal studies have shown adverse effects, and there are no adequate human studies confirming safety during pregnancy. Therefore, it is not considered safe without careful risk-benefit analysis. Teratogenicity and fetal toxicity are concerns due to its action on muscle fibers and potential systemic effects. Pregnant clients should consult their provider before initiating or continuing dantrolene therapy.

Choice D rationale: Dantrolene does not directly affect calcium levels in the bloodstream. Its mechanism involves inhibition of calcium release within muscle cells, not systemic calcium metabolism. Routine calcium monitoring is not required unless the client has a separate condition affecting calcium homeostasis. Normal serum calcium levels range from 8.5 to 10.5 mg/dL. The primary lab concern with dantrolene is hepatotoxicity, necessitating regular liver function tests, not calcium surveillance. This statement reflects a misunderstanding of the drug’s effects.