Pharmacology and Drug Calculations Flashcards

A patient taking warfarin is prescribed ciprofloxacin. What INR change should the nurse anticipate?

Answer: INR will increase — bleeding risk rises due to CYP2C9 inhibition

Fluoroquinolones (e.g., ciprofloxacin) inhibit CYP2C9, which metabolizes warfarin. Reduced warfarin clearance leads to increased serum warfarin levels and elevated INR. Additionally, broad-spectrum antibiotics reduce gut flora that produces vitamin K, further elevating INR.

A nurse is teaching a patient about taking metformin. Which instruction is most important?

Answer: Report persistent nausea, vomiting, abdominal pain, or muscle pain — possible lactic acidosis

The rare but potentially fatal complication of metformin is lactic acidosis. Symptoms include nausea, vomiting, abdominal pain, and muscle pain (myalgia). These should be reported immediately. Metformin is best taken with meals to reduce GI side effects.

A patient is prescribed IV methylprednisolone 1 g as a single dose. The available vial contains 500 mg/8 mL. How many mL should be administered?

Answer: 16 mL

Concentration = 500 mg/8 mL = 62.5 mg/mL. Volume = 1,000 mg ÷ 62.5 mg/mL = 16 mL. Alternatively: (1,000 mg/500 mg) × 8 mL = 2 × 8 = 16 mL.

A patient develops urticaria and difficulty breathing after the first dose of IV penicillin. The priority medication to administer is:

Answer: Epinephrine (adrenaline) 0.3–0.5 mg IM

Anaphylaxis is a life-threatening allergic reaction requiring immediate epinephrine (adrenaline) 0.3–0.5 mg IM into the lateral thigh as first-line treatment. Antihistamines and corticosteroids are adjuncts but do not treat the life-threatening bronchospasm and hypotension as rapidly as epinephrine.

A nurse is reviewing medications for a patient with renal failure (eGFR 25 mL/min). Which medication requires dose reduction?

Answer: Metformin — contraindicated; increase in lactic acidosis risk

Metformin is contraindicated (not just dose-reduced) when eGFR is <30 mL/min due to the risk of lactic acidosis from drug accumulation. Furosemide often needs dose increases (not reduction) in renal failure. ACE inhibitors require monitoring but are sometimes continued carefully.

A patient is prescribed clopidogrel after coronary stent placement. Which drug combination creates the most dangerous interaction?

Answer: Omeprazole — reduces clopidogrel activation via CYP2C19 inhibition

Clopidogrel requires hepatic activation by CYP2C19. Proton pump inhibitors (especially omeprazole) strongly inhibit CYP2C19, reducing clopidogrel's active metabolite levels by up to 47%, potentially increasing the risk of in-stent thrombosis. Pantoprazole has less CYP2C19 inhibition.