Pharmacology and Drug Calculations Flashcards

A 68 kg patient in a Saudi hospital ICU is prescribed dopamine at 7 mcg/kg/min. The available solution is dopamine 400 mg in 250 mL NS. What is the correct infusion rate in mL/hr?

Answer: 17.9 mL/hr

First calculate the concentration: 400 mg/250 mL = 1.6 mg/mL = 1600 mcg/mL. Dose required = 7 mcg/kg/min × 68 kg = 476 mcg/min. Convert to mcg/hr: 476 × 60 = 28,560 mcg/hr. Rate = 28,560 ÷ 1600 = 17.85 mL/hr ≈ 17.9 mL/hr. This is a weight-based vasopressor calculation commonly tested at the advanced level.

Under the Saudi Food and Drug Authority (SFDA) controlled substance regulations, which schedule classification applies to tramadol, and what is the maximum single-dispensing quantity permitted in outpatient pharmacies without a special narcotics prescription form?

Answer: Schedule IV; 30-day supply with standard prescription

The SFDA classifies tramadol as a Schedule IV controlled substance. It can be dispensed in outpatient pharmacies with a standard prescription for up to a 30-day supply without requiring the specialized narcotics (Schedule I–III) prescription form. This distinguishes it from stronger opioids like morphine (Schedule I under SFDA), which require the green narcotics prescription form and strict quota controls.

A nurse is preparing heparin infusion for a 80 kg patient using a weight-based protocol. The order reads: bolus 80 units/kg IV, then infusion at 18 units/kg/hr. Available: heparin 25,000 units in 250 mL D5W. After administering the bolus separately, at what rate (mL/hr) should the infusion pump be set?

Answer: 14.4 mL/hr

Infusion dose = 18 units/kg/hr × 80 kg = 1,440 units/hr. Concentration = 25,000 units ÷ 250 mL = 100 units/mL. Rate = 1,440 ÷ 100 = 14.4 mL/hr. The bolus (80 × 80 = 6,400 units) is given separately and does not affect the infusion rate calculation. This is a high-alert medication requiring double-checking.

A patient receiving vancomycin develops a serum trough level of 22 mg/L (target: 10–20 mg/L). The current regimen is 1,250 mg every 12 hours. According to pharmacokinetic principles used in Saudi hospital antimicrobial stewardship programs, what is the MOST appropriate initial nursing action?

Answer: Hold the next dose and notify the physician immediately

A vancomycin trough of 22 mg/L exceeds the therapeutic range (10–20 mg/L) and places the patient at risk for nephrotoxicity. The nurse must hold the next scheduled dose and immediately notify the physician or clinical pharmacist for dose adjustment, per SCFHS nursing scope of practice. Independently reducing the dose (option C) is outside the nurse's scope, and simply documenting (option B) or altering infusion time (option D) do not address supratherapeutic levels appropriately.

A 55 kg female patient with CrCl of 28 mL/min (moderate renal impairment) is prescribed metformin 1,000 mg twice daily for Type 2 diabetes. According to Saudi clinical pharmacy guidelines aligned with SFDA labeling, what is the MOST appropriate nursing response?

Answer: Question the order and withhold the medication pending physician review, as metformin is contraindicated below CrCl 30 mL/min

Metformin is contraindicated when CrCl falls below 30 mL/min due to the risk of lactic acidosis from drug accumulation. A CrCl of 28 mL/min is below this threshold. The nurse should withhold the dose and contact the prescribing physician for order clarification or an alternative agent. This aligns with SFDA-approved metformin prescribing information and Saudi MOH formulary guidance. Self-adjusting the dose (option C) is outside nursing scope and still dangerous at this CrCl.

A nurse is preparing a magnesium sulfate infusion for a 70 kg eclamptic patient. The order reads: 4 g IV loading dose over 20 minutes, then 2 g/hr maintenance. Available: 50% MgSO₄ solution (500 mg/mL). How many mL of the 50% solution are needed for the loading dose only?

Answer: 8 mL

A 50% magnesium sulfate solution contains 500 mg/mL. The loading dose required is 4 g = 4,000 mg. Volume needed = 4,000 mg ÷ 500 mg/mL = 8 mL. This 8 mL is then typically diluted (e.g., in 100 mL NS) before administration over 20 minutes. Errors in calculating undiluted MgSO₄ volumes are a common cause of fatal overdose; this is why it is classified as a high-alert medication in Saudi hospital accreditation standards (CBAHI/JCI).