A 72-year-old man on warfarin 5 mg daily for atrial fibrillation develops community-acquired pneumonia and is prescribed erythromycin 500 mg four times daily. Three days later, he presents with gingival bleeding and hematuria. Vital signs: BP 128/76, HR 92, RR 18, Temp 37.2°C, SpO2 98%. Laboratory findings show INR 9.2 (previously 2.8), hemoglobin 10.2 g/dL (baseline 13.5), and PT 68 seconds. Physical exam reveals scattered gingival oozing and bilateral crackles on auscultation. Chest X-ray confirms right lower lobe pneumonic infiltrate. Which mechanism best explains this drug interaction?
- A)Decreased warfarin metabolism due to cytochrome P450 inhibitionGABARITO
- B)Irreversible inhibition of platelet cyclooxygenase
- C)Enhanced renal elimination of warfarin by urine alkalinization
- D)Reduced warfarin bioavailability from first-pass metabolism
- E)A pharmacodynamic decrease in efficacy caused by receptor downregulation
Explicação
Macrolides such as erythromycin can inhibit cytochrome P450 enzymes and increase levels of coadministered drugs metabolized by the liver. Warfarin accumulation raises the INR and causes bleeding. The time course and medication combination strongly support a me... Ver explicação completa e trilha adaptativa →