Calculations question

1a) A physician writes the following prescription order for an 8month old infant (weight 10.5 lbs)


Propranolol suspension 3.4mg/kg/day given twice a day x 1 month


Your institution’s formula is as follows:

i) The pharmacy prepares 500 ml of the above solution to keep in stock. How much (in ml) of the above suspension would the patient need for each dose? (3 marks)

ii) You are asked to freshly prepare a 28-day supply of the above prescription for the patient. How much of each ingredient would you need to ensure sufficient amount but minimal excess? (2 marks)

b) A 42 year old male (weight 62kg) requires KCl supplementation due to hypokalaemia. The physician orders for 40 mEq KCl to be given intravenously. For KCl to be infused peripherally, hospital policy recommends 10 mEq/100ml as the maximum concentration and a maximum administration rate of 10 mEq/hr. Your pharmacy stocks KCl 20mEq/50ml solution.

i) How would you prepare the KCl solution for peripheral administration to the patient and at what rate would you instruct the nurse to administer the medication? (2 marks)

ii) What is the total osmolarity (mOsmol/L) of the above IV solution if 0.9% NaCl was used as the diluent? (KCl = 74.5; NaCl= 58.4) (3 marks)

c) A 20 year old male (weight 125 lbs) is prescribed ranitidine 1mg/kg/hr x 12 hours. The pharmacy stocks 150 mg/6ml solution for injection. The manufacturer recommends continuous IV infusion to be diluted to a concentration of 0.5 mg/ml.

i) How many stock vials would you need for the prescription order of 12-hour supply or ranitidine infusion for the patient? (2 marks)

ii) How much diluent would you need to prepare the order? (2 marks)

iii) At what rate (ml/min) would you instruct the nurse to administer the prepared solution? (2 mark)

d) A patient (weight 22 kg, height 124 cm) is prescribed Acyclovir 450 mg/m2 IV Q8 hours. How much acyclovir (in mg) would be needed per dose?

Mosteller equation: BSA (m2) = square root of {[height(cm) x weight(kg)]/3600}

(1 mark)

e) A patient (weight 45 kg) received vancomycin 900 mg IV Q8h for MRSA pneumonia. The drug was infused over 60 minutes. Trough concentrations measured after the third dose was 22 mcg/mL. (Vd = 0.4 L/kg)

i) What is the half life of elimination of the drug? (2 marks)

ii) How long will it take for the trough level to reach 18 mcg/ml (1 mark)

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