Immediate IV Fluid Resuscitation with Normal Saline
The most appropriate additional therapy is IV bolus of normal saline. This patient presents with acute gastroenteritis causing severe volume depletion (dry mucous membranes, tachycardia, elevated creatinine from 1.5 mg/dL baseline), and she is at high risk for metformin-associated lactic acidosis (MALA) given her acute illness with vomiting, diarrhea, and dehydration while taking metformin 1, 2.
Critical First Steps: Volume Resuscitation and Medication Management
Immediate fluid resuscitation is the priority because:
- Volume depletion triggers sick day medication guidance (SDMG) - vomiting and diarrhea resulting in significant fluid losses are established triggers requiring immediate intervention 1
- Dehydration while on metformin creates life-threatening risk - the combination of volume depletion, acute kidney injury, and continued metformin use can precipitate MALA with mortality rates of 0.015 per 1000 patient-years 2, 3
- Her elevated creatinine (1.5 mg/dL) indicates acute kidney injury - metformin accumulates when renal function declines, and the drug is contraindicated when eGFR falls below 30 mL/min/1.73m² 2, 1
Medications That Must Be Stopped Immediately
Temporarily discontinue these medications per sick day guidance 1:
- Metformin - must be stopped immediately due to vomiting/diarrhea causing dehydration and risk of lactic acidosis 1, 2, 4
- Lisinopril (ACE inhibitor) - should be held during acute illness with volume depletion to prevent worsening renal function 1, 5
- The combination of metformin and ACE inhibitors during dehydration is particularly dangerous, with multiple case reports of severe lactic acidosis (pH 6.60-6.94) requiring hemodialysis 6
Why Other Options Are Incorrect
Emergent hemodialysis - not indicated unless severe lactic acidosis develops (pH <7.0, lactate >5 mmol/L, metformin level >5 mcg/mL) 2, 7
Administration of lisinopril - contraindicated; ACE inhibitors should be withheld during volume depletion and acute illness 1, 5
Subcutaneous insulin - inappropriate as initial therapy; her glucose of 260 mg/dL is elevated but not critically high, and addressing dehydration takes priority 1
Monitoring and Follow-Up After Fluid Resuscitation
Once volume status is restored, assess for:
- Signs requiring urgent care contact - she already meets criteria with >4 episodes of vomiting in 12 hours and inability to keep fluids down 1
- Renal function recovery - check creatinine and eGFR before restarting metformin; metformin should not be restarted if eGFR remains <30 mL/min/1.73m² 1, 2
- Symptoms lasting >72 hours - if vomiting/diarrhea persists beyond 72 hours despite self-management, she requires HCP assistance 1
When to Restart Medications
Metformin can be restarted only when 1, 2:
- Patient is euvolemic and tolerating oral intake
- Renal function has returned to baseline (eGFR ≥30 mL/min/1.73m²)
- No ongoing acute illness
Lisinopril can be restarted when 1:
- Volume status is restored
- Blood pressure is stable
- Renal function is at baseline
Common Pitfall to Avoid
Do not continue metformin during acute gastroenteritis - the combination of dehydration, vomiting, and continued metformin use has resulted in fatal cases of lactic acidosis, particularly when combined with ACE inhibitors 2, 4, 6. The FDA label specifically warns that "withholding of food and fluids during surgical or other procedures may increase the risk for volume depletion, hypotension, and renal impairment" and recommends temporary discontinuation 2.