Critical INR, New Antibiotic, and a Note That Says Continue
A 72-year-old woman with atrial fibrillation and heart failure is admitted with a urinary tract infection. Her medications include warfarin 5 mg daily, spironolactone 25 mg daily, carvedilol, and furosemide. Twelve days ago, trimethoprim-sulfamethoxazole was started. Today her INR is 6.8, hemoglobin 11.8 g/dL, platelets 180,000/µL, and potassium 5.9 mmol/L. She denies bleeding but has new bruising on both forearms. The INR was 2.4 two weeks ago. The laboratory phones the critical INR to the unit; the nurse documents a read-back at 14:35. The resident’s progress note says “continue warfarin, recheck INR in 1 week” and does not mention the antibiotic or the potassium. The transcriptionist is entering the daily lab and medication note and sees both critical values. The note must be authenticated before the end of the shift.
1. Explain the likely drug–drug interaction and laboratory findings. What in the record supports over-anticoagulation and hyperkalemia?
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Trimethoprim-sulfamethoxazole can raise the INR in a patient taking warfarin by inhibiting CYP2C9-mediated warfarin metabolism and, to some extent, by protein-binding displacement. The INR rose from 2.4 to 6.8 after the antibiotic was started, and new forearm bruising supports excessive anticoagulant effect even without major bleeding. The potassium of 5.9 mmol/L is also concerning: trimethoprim blocks renal tubular potassium secretion, and spironolactone is a potassium-sparing diuretic, so the combination can produce hyperkalemia. Hemoglobin and platelets do not show a clear alternative explanation for the bruising. The note’s instruction to continue warfarin and recheck in one week is clinically inconsistent with an INR of 6.8 and a recent interacting antibiotic, but the transcriptionist must not independently alter the order. The role is to recognize the discrepancy, transcribe accurately, and escalate through the proper channel.
2. What should the transcriptionist do with the conflicting resident note and the critical values? What must not be done?
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The transcriptionist should enter the laboratory values exactly as reported, preserve the resident’s documented order, and immediately flag the critical INR and potassium to the responsible clinician or charge nurse according to facility policy. The critical-result notification and read-back should be documented only if they actually occurred, including time, recipient, and who confirmed the result. The transcriptionist should not write “warfarin held” or “potassium treated” unless a clinician has ordered it. The transcriptionist should not independently call the pharmacy for a dose change, alter the note to match personal clinical judgment, or omit the resident’s “continue warfarin” statement. If the clinician cannot be reached, escalate per policy. A query or safety flag should make clear that the transcriptionist identified a discrepancy but is not prescribing.
3. How should the medication and laboratory lines be styled to avoid ambiguity? Give examples.
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Use exact drug names, doses, routes, and frequencies, and avoid unsafe abbreviations. Write “trimethoprim-sulfamethoxazole” on first use rather than an ambiguous shorthand. Laboratory values should carry the correct units: INR 6.8 (INR is unitless), potassium 5.9 mmol/L, hemoglobin 11.8 g/dL, and platelets 180,000/µL. Preserve the resident’s wording “recheck INR in 1 week” rather than converting it to “in 7 days,” because conversion can look like a new order even when equivalent. If the facility permits “K+” in a defined abbreviation list, follow that list; otherwise use “potassium.” A notification line should be factual, for example: “Critical INR 6.8 phoned to Dr. X at 14:35; read-back confirmed by RN Y.” Do not add that line unless it is true and documented by the appropriate clinician.