A patient is prescribed haloperidol 2 mg orally twice daily for schizophrenia. If haloperidol is available in 1 mg tablets, how many tablets will the patient need for one week?

To determine the number of tablets needed for one week, work through the calculation step by step. The prescribed dose is 2 mg twice daily, which equals 4 mg per day. Over seven days, the total dose required is 4 mg × 7 days = 28 mg. Since each tablet contains 1 mg, the patient needs 28 mg ÷ 1 mg per tablet = 28 tablets for one week. The keyed answer of 28 tablets is correct. The distractor of 14 tablets represents only a once-daily dose calculation, as if the nurse multiplied only one 2 mg dose by 7 days, ignoring the 'twice daily' instruction. The distractor of 21 tablets could arise from miscounting the days or miscalculating the daily dose. The distractor of 24 tablets has no clear mathematical basis from the given data and likely results from rounding or arithmetic error. Careful attention to the dosing frequency, 'twice daily,' is the critical step students most commonly miss in this type of calculation. Always identify frequency first, calculate the total daily dose, and then multiply by the number of days to find the weekly supply needed.