Vancomycin trough of 32 mg/L with a rising creatinine on a busy surgical ward

The trough is grossly supratherapeutic and the patient has evolving acute kidney injury; continuing the same dose is unsafe.

Calculations (Cockcroft-Gault, actual body weight):

• At admission, creatinine 1.4 mg/dL: (140 - 70) x 65 / (72 x 1.4) = 4550 / 100.8 = about 45 mL/min.
• Today, creatinine 2.6 mg/dL: 4550 / 187.2 = about 24 mL/min.

Interpretation:

• A trough of 32 mg/L is well above the usual target of 10 to 15 mg/L for uncomplicated infection, or 15 to 20 mg/L where a trough is used as a surrogate for an AUC of 400 to 600 mg·h/L. Absorption is not the issue here - clearance has fallen while the dose stayed fixed, so drug is accumulating.
• The creatinine has nearly doubled in three days. That is vancomycin-associated nephrotoxicity until proven otherwise, and it is being compounded by piperacillin-tazobactam (recognised synergistic nephrotoxicity with vancomycin), ibuprofen (afferent vasoconstriction), furosemide (volume depletion) and enalapril (reduced glomerular filtration and hyperkalaemia risk).
• Increasing foot pain with no fever is a reminder that the infection is not controlled; this is not a reason to give more vancomycin but a reason to ensure surgical source control and re-image the foot.

Do not continue the same dose. Hold the next dose, then re-dose by weight and renal function, and monitor with a measured level.

Proposed plan:

• Hold the current 8 am dose pending clinical review and repeat electrolytes.
• Re-dose at 15 mg/kg actual body weight = about 1000 mg, with the interval set by the current creatinine clearance of roughly 24 mL/min - typically every 24 hours, extended to every 48 hours if renal function continues to fall.
• Check a trough immediately before the second or third dose (steady state is delayed in renal impairment), aiming for 15 to 20 mg/L while the infection is severe. Because AUC software is unavailable, use the trough as the surrogate and document the assumption.

Response to the surgical team: 'Until the trough comes down' is the wrong frame - the trough will only come down if the dose is changed, because clearance is now roughly half what it was at admission. Meanwhile the kidneys are being exposed to a nephrotoxic load.

Modifiable factors to put in the same note: stop ibuprofen (use paracetamol), review the need for furosemide and enalapril with the medical team, and de-escalate piperacillin-tazobactam - the cultures grow MRSA only, so there is no Gram-negative cover to justify keeping it. If renal function continues to deteriorate, linezolid 600 mg twice daily (no renal adjustment) or daptomycin are the alternatives to raise with the consultant.

A short, dated plan that the ward can actually follow:

• Daily serum creatinine, urea and electrolytes (potassium is at risk from enalapril plus developing AKI), and a fluid balance chart with daily weight.
• Vancomycin level before the relevant dose as above; do not redraw a trough during the same dosing interval and act on it as if it were steady state.
• Urinalysis to look for casts or protein, and ask the nursing staff to report urine output below 0.5 mL/kg/hour.
• Repeat wound inspection or imaging to confirm source control, since increasing foot pain with a therapeutic level would suggest undrained infection rather than under-dosing.
• Review the level and creatinine at 48 to 72 hours and adjust the interval again - the commonest error here is to re-dose at 24 hourly and then leave it.

Communication: speak to the surgical team and the medical team together, write the recommendation in the case record with the calculation shown, and tell the nursing staff explicitly that the previous order is cancelled. Record the discussion, because the disagreement about continuing the same dose has to be visible in the notes if the creatinine climbs further.