PTCB CPhT PTCE Question # 60 Topic 7 Discussion

To determine the correct volume of amoxicillin suspension per dose, use the given concentration and dose.

Prescription dose:150 mg per dose

Suspension concentration:250 mg per 5 mL

Formula to calculate volume needed:Volume (mL)=Prescribed dose (mg)Concentration (mg/mL)\text{Volume (mL)} = \frac{\text{Prescribed dose (mg)}}{\text{Concentration (mg/mL)}}Volume (mL)=Concentration (mg/mL)Prescribed dose (mg)​

Step 1: Identify Given InformationStep 2: Calculate150 mg250 mg/5 mL=150×5250=750250=3 mL\frac{150 \text{ mg}}{250 \text{ mg/5 mL}} = \frac{150 \times 5}{250} = \frac{750}{250} = 3 \text{ mL}250 mg/5 mL150 mg​=250150×5​=250750​=3 mL

Thus, the patient should take3 mL per dose.

B. 4 mL→ Incorrect; this would correspond to a different strength.

C. 5 mL→ Incorrect; this would deliver250 mg, which is incorrect.

D. 6 mL→ Incorrect; this would deliver300 mg, exceeding the prescribed dose.

Other Answer Choices Explained:References:

PTCB PTCE Exam Content Outline (Pharmaceutical Calculations – Dosage & Volume Calculations)

USP <795> Guidelines for Nonsterile Compounding & Drug Dilution

Lexicomp Drug Monograph for Amoxicillin Suspension