PH1.1-13 | General Pharmacology Foundations — Assignment

CLINICAL SCENARIO

You are a Year-2 medical student rotating in the general medicine ward. A 68-year-old man with hypertension, type 2 diabetes, and chronic kidney disease (CKD stage 3b — eGFR 32 mL/min/1.73 m²) is admitted with a productive cough and fever. He is diagnosed with community-acquired pneumonia and prescribed levofloxacin 750 mg once daily. You notice he is already on metformin 1000 mg twice daily, enalapril 10 mg once daily, and amlodipine 5 mg once daily. In your post-ward review, your consultant asks you to work through the pharmacological principles underpinning the management of this complex patient.

Levofloxacin is prescribed by its generic (INN) name. (a) Explain the three layers of drug nomenclature (chemical, generic/INN, brand name) using levofloxacin as an example. (b) Justify — using rational drug use principles and evidence-based medicine — why the Essential Medicines List and rational prescribers prefer the INN. (c) Identify ONE drug in this patient's existing regimen where brand-name confusion could be clinically dangerous, and explain why.

The patient has CKD stage 3b (eGFR 32 mL/min/1.73 m²). (a) Explain how reduced GFR affects the pharmacokinetics of levofloxacin and metformin — specifically addressing clearance, half-life, and risk of drug accumulation for each. (b) The BNF recommends levofloxacin 500 mg once daily (not 750 mg) when eGFR is 20–49 mL/min. Explain the pharmacokinetic rationale for this dose reduction. (c) What is the key safety risk if metformin is continued at standard doses in a patient with this level of renal impairment? Provide the pharmacokinetic basis for your answer.

(a) Describe the mechanism of action of levofloxacin, identifying the specific molecular target and the consequence of drug-target interaction. (b) Enalapril is an ACE inhibitor and amlodipine is a dihydropyridine calcium channel blocker. Explain the pharmacodynamic rationale for combining these two drugs for hypertension — state whether this is a synergistic, additive, or complementary combination, and explain the basis. (c) If the patient developed a severe chest infection requiring gentamicin, would combining it with levofloxacin be rational? Apply PK-PD synergism principles to justify your answer.

(a) The patient develops prolonged QT interval 48 hours after starting levofloxacin. Apply the WHO-UMC causality framework to assess this adverse event. State which causality category you would assign and justify each criterion. (b) Should this reaction be reported to the hospital pharmacovigilance system? Explain what pharmacovigilance is, who should report, and which national body in India receives ADR reports under the PvPI programme. (c) Identify ONE clinically significant pharmacokinetic drug interaction possible in this patient's regimen. Explain the mechanism (induction/inhibition/protein displacement) and the clinical consequence.

(a) This patient is 68 years old. Identify THREE specific pharmacokinetic or pharmacodynamic changes in the elderly that could alter levofloxacin's safety profile in this patient. (b) The patient is unable to swallow tablets and asks about IV levofloxacin. Compare the oral and intravenous routes for levofloxacin in this patient — specifically discussing bioavailability, first-pass metabolism (or lack thereof), onset, and route-appropriate dose equivalence. (c) Synthesise your analysis: Is this overall drug regimen rational for this patient? Identify ONE change you would recommend and justify it using the principles of rational drug use.