The healthcare provider orders Compazine 10 mg IM now. The concentration available is Compazine 5 mg/mL. How many mL will the patient receive?

Choice A reason: Synthesis of more receptor sites (upregulation) typically occurs with receptor antagonists, not agonists, as the body compensates for blocked receptors. This would increase drug sensitivity, not decrease effectiveness. For most medications, continuous exposure leads to desensitization, not receptor proliferation, making this choice incorrect for explaining tolerance.

Choice B reason: Decreased receptor selectivity implies a drug binding to unintended receptors, causing varied effects, not reduced efficacy. Tolerance results from receptor desensitization, not altered selectivity. This mechanism doesn’t explain the patient’s “immunity” to the drug’s therapeutic effects, making this choice scientifically inaccurate for the scenario.

Choice C reason: Desensitization occurs when continuous drug exposure reduces receptor responsiveness, leading to tolerance. For example, opioid receptors downregulate or internalize with prolonged agonist exposure, decreasing drug efficacy. This explains the patient’s perception of “immunity” as the drug’s effect diminishes over time, making this the correct choice.

Choice D reason: The body does not produce antagonists to compete with drugs for receptor sites. Tolerance arises from receptor desensitization or metabolic changes (e.g., enzyme induction), not endogenous antagonist production. This mechanism is not a recognized pharmacological process for reduced drug effectiveness, making this choice incorrect.

Choice A reason: To calculate the volume, divide the ordered dose (8 mg) by the concentration (5 mg/mL): 8 ÷ 5 = 1.6 mL. Choice A (1.4 mL) underestimates the volume, delivering only 7 mg (1.4 × 5), which is insufficient for the prescribed dose, making it incorrect for accurate medication administration.

Choice B reason: Calculating 8 mg ÷ 5 mg/mL yields 1.6 mL. Choice B (1.8 mL) would deliver 9 mg (1.8 × 5), exceeding the ordered dose. This overdose could increase the risk of sedation or respiratory depression, as Valium (diazepam) is a benzodiazepine with potent CNS effects, making this choice incorrect.

Choice C reason: The correct volume is 8 mg ÷ 5 mg/mL = 1.6 mL. Choice C (1.2 mL) delivers only 6 mg (1.2 × 5), which is below the prescribed dose. This underdose could result in inadequate therapeutic effects, such as insufficient anxiety relief or seizure control, making it an incorrect choice.

Choice D reason: Dividing the ordered dose (8 mg) by the concentration (5 mg/mL) gives 8 ÷ 5 = 1.6 mL. This volume accurately delivers the prescribed 8 mg of Valium, ensuring therapeutic efficacy for conditions like anxiety or seizures while minimizing risks of over- or under-dosing, making it the correct choice.