Clinical Case Scenario

A 26‑year‑old woman, five months post–renal transplant for autosomal dominant polycystic kidney disease, was admitted to the ICU with hematemesis, fever, and altered sensorium. On arrival, she was hypotensive (BP 84/65 mmHg) with severe anemia (Hb 5 g/dL).

After initial resuscitation and elective intubation for airway protection, she underwent CT angiography, which revealed multiple aneurysms in the coeliac and mesenteric arterial tree with active bleeding from the gastroduodenal artery (GDA). She underwent successful embolization of the GDA and was transferred back to the ICU for post‑procedural care.

She was empirically started on piperacillin–tazobactam and vancomycin. Blood cultures grew Enterococcus faecium, prompting escalation to meropenem, voriconazole, and trimethoprim–sulfamethoxazole for broader coverage. Given her recent transplant, the nephrology team advised continuation of immunosuppressants. All routine medications were continued except aspirin (withheld due to bleeding risk). Her whole blood  tacrolimus trough level  was subtherapeutic (5 ng/mL), so the dose was increased from 4 mg/day to 6 mg/day.

Her condition stabilized, and she was extubated on day 6.

On day 8, she developed a headache and severe hypertension (BP 180/100 mmHg). Neurological examination showed no focal deficits except for tremors. Later that evening, she developed visual disturbances and progressive coma.

Laboratory Findings

• Hb: 8.2 g/dL
• WBC: 12,000/µL
• CRP: 39 mg/L
• AST: 654 U/L, ALT: 345 U/L
• Bilirubin: 61 µmol/L
• Creatinine: 183 µmol/L (eGFR 37 mL/min/1.73m²)
• Potassium: 6.3 mmol/L
• pH: 7.18, pCO₂: 20 mmHg, HCO₃⁻: 14 mmol/L, BE: –9.3
• Phosphate: 0.6 mmol/L

Wrong Answer: A. Initiating high dose corticosteroids in this scenario may not be of utility as there is no evidence of biopsy proven graft rejection .

Wrong Answer: B. Performing CSF study to exclude possibility of an intracranial infection is not appropriate in this situation as the patient’s acute worsening does not seem to be due to infection baring a fever or shock.

Wrong Answer: C. Tacrolimus can precipitate PRES due to uncontrolled hypertension; However the identification and elimination of the inciting drug followed by renal replacement therapy and blood pressure control are the most crucial components of the management plan than shifting for MRI.

Right Answer: D. Temporarily discontinue tacrolimus, send samples for whole blood tacrolimus levels corrected for hematocrit, check for pharmacokinetic interactions and initiate CRRT

Explaination:

Tacrolimus is a widely used immunosuppressant used following solid organ transplants like kidney, liver, heart and lung. It is a calcineurin inhibitor with a narrow therapeutic window of 5-15 ng/mL . Acute toxicity of tacrolimus typically manifests as AKI in the form of acute tubular necrosis , type IV RTA and neurotoxicity in the form of seizures and coma. Tacrolimus also causes post -transplant hypertension in around 70% of transplant recipients, the mechanism of which is multifactorial ranging from endothelial dysfunction , impaired renal auto regulation to renal vasoconstriction and sympathetic over activation. It also causes hyperglycemia from direct pancreatic -Beta cell apoptosis and peripheral insulin resistance amongst multiple other mechanisms
The new onset tremors , hyperglycemia , hyperkalemia ,metabolic acidosis along with neurological symptoms strongly point towards a tacrolimus toxicity .
Once absorbed, tacrolimus is primarily metabolized by CYP3A4/5 and distributed mainly into erythrocytes . Although the unbound fraction of the drug is the active one , the bound fraction of the drug in whole blood is the only standard test available to guide therapy. Several factors are known to precipitate toxicity like pharmacodynamic factors ,hypoalbuminemia , haematocrit values, shock state, renal failure, hepatic failure , etc .
Because >95% of tacrolimus is bound to red blood cells (RBCs) and plasma proteins. In anemic patients, standard trough levels may falsely indicate sub-therapeutic tacrolimus concentrations due to reduced erythrocyte binding. However, the unbound, pharmacologically active fraction, which enters tissues and causes immunosuppression/toxicity, may actually be elevated. Since routine monitoring measures total tacrolimus (bound + unbound) rather than the unbound fraction, hematocrit-corrected whole blood tacrolimus concentration using a normogram is recommended.

Several factors have co-precipitated an acute toxicity in this scenario. Tacrolimus is a drug metabolized by CYP3A45 and drugs that inhibit CYP3A45 like voriconazole can increase tacrolimus levels. Furthermore, her whole blood tacrolimus levels done initially had shown a false underestimation of the unbound fraction ; Subsequently she also had a dosage increase based on those spuriously low values , assuming a sub-therapeutic range further contributing to toxicity .Besides , female sex , infections and shock states impairing the metabolism are other risk factors.
Tacrolimus is non dialyzable ; Hence CRRT in this case is for hyperkalemia and metabolic acidosis and not for facilitating removal of tacrolimus. Thus a multidisciplinary management involving intensivists, nephrologists, clinical pharmacist is pivotal for such patients.

TAKE HOME POINTS:

● Tacrolimus is a widely used post transplant immunosuppresant with narrow therapeutic window (5–15 ng/mL) → toxicity can occur even at “normal” or “low” trough levels if hematocrit is low.
● It is an important cause of AKI apart from routine causes of renal injury like graft rejection , infections,and post renal causes.
● Clinical red flags: tremors, seizures, coma, hypertension, hyperkalemia, metabolic acidosis, hyperglycemia, AKI.
● Drug interactions matter: CYP3A4/5 inhibitors (e.g., voriconazole) markedly raise tacrolimus levels.
● Lab pitfalls: whole‑blood troughs may underestimate toxicity in anemia → unbound fraction is the active component.
● Definitive management: stop or reduce tacrolimus, control BP, correct metabolic derangements.
● Tacrolimus is non‑dialyzable → CRRT only for metabolic/uremic indications, not for drug clearance.
● Multidisciplinary approach (ICU, nephrology, transplant team, pharmacist) is essential.