A patient is prescribed an intramuscular dose of 150 mg of an antipsychotic drug. The available vial contains 200 mg/mL. How many milliliters should the nurse administer?

Choice A reason: Administering 0.5 mL would result in a total dose of 100 mg, calculated by multiplying 0.5 mL by the concentration of 200 mg/mL. This represents a subtherapeutic dose that fails to meet the 150 mg prescription, potentially leading to inadequate control of the patient's acute psychiatric symptoms. Choice B reason: The required volume is calculated using the formula: Desired dose / Have concentration = Volume. In this clinical scenario, 150 mg / 200 mg/mL = 0.75 mL. This precise volume ensures the delivery of the exact milligram dosage required for the intramuscular injection while maintaining pharmacological safety standards. Choice C reason: Administering 1 mL would provide 200 mg of the antipsychotic medication, which is a 50 mg surplus over the ordered amount. Such a medication error increases the risk of dose-dependent adverse effects, such as extrapyramidal symptoms, profound sedation, or acute dystonia in the psychiatric patient. Choice D reason: A volume of 1.5 mL would deliver 300 mg of the drug, which is double the prescribed therapeutic dose. This significant overdose could lead to severe neurotoxicity, cardiovascular complications, or neuroleptic malignant syndrome, representing a major failure in medication administration safety protocols and nursing vigilance.