A patient who has been receiving cimetidine 400 mg one tablet b.

• Needed dose: 400 mg per dose.

• Available concentration: 300 mg/5 mL.

• Use proportion/dimensional analysis:

- mL=400 mg×5 mL300 mg=2000300 mL=6.6‾ mL≈6.7 mL\text{mL} = 400\ \text{mg} \times \frac{5\ \text{mL}}{300\ \text{mg}} = \frac{2000}{300}\ \text{mL} = 6.\overline{6}\ \text{mL} \approx 6.7\ \text{mL}mL=400 mg×300 mg5 mL​=3002000​ mL=6.6 mL≈6.7 mL.

• Thus, 6.7 mL per dose is required.

References (Pharmacy Technician documents / Study Guides):

• PTCB/ExCPT pharmacy calculations—dose-concentration conversions using ratio-proportion or dimensional analysis.

• Nonsterile compounding and dispensing references—accurate liquid dose calculations from mg/mL strengths.