What does a Tacrolimus level of 11.4 mcg/L indicate?

Tacrolimus Level of 11.4 mcg/L: Clinical Interpretation

A tacrolimus level of 11.4 mcg/L (ng/mL) falls within the therapeutic range for most transplant patients and indicates adequate immunosuppression, though the appropriateness depends on the time post-transplant and specific clinical context. 1, 2

Therapeutic Range Context

For most solid organ transplant recipients, this level is appropriate:

• The recommended therapeutic trough range is 5-15 ng/mL for transplant patients, with 11.4 ng/mL falling comfortably in the middle of this range 1
• In the early post-transplant period (first 1-2 months), most centers target the higher end of 10-15 ng/mL, making 11.4 ng/mL appropriate 2
• For long-term maintenance (beyond first year), targets are typically 5-10 ng/mL, meaning 11.4 ng/mL is slightly elevated but may still be acceptable depending on rejection risk 2

Time-Dependent Interpretation

The clinical significance varies by transplant timeline:

• First month post-transplant: 11.4 ng/mL is appropriate and associated with reduced acute rejection risk. Levels >7 ng/mL in the first month are associated with an 86% decreased risk of acute rejection compared to levels of 4-7 ng/mL 3
• Months 1-12: This level remains within target for most protocols 1, 2
• Beyond first year: Consider whether dose reduction toward 5-10 ng/mL range is appropriate if the patient is stable 2

Clinical Actions Required

At this level, the following monitoring is essential:

• Continue current dosing if the patient is in the early post-transplant period 1, 2
• Monitor for toxicity even at therapeutic levels: Check renal function (creatinine), glucose, potassium, magnesium, blood pressure, and CBC 1
• Assess for drug interactions: Any recent addition or removal of CYP3A4 inhibitors or inducers requires close monitoring, as these can significantly alter tacrolimus levels 1
• Evaluate clinical context: If the patient has severe diarrhea or gastrointestinal illness, this level may be falsely elevated due to altered intestinal P-glycoprotein function 4

Monitoring Frequency at This Level

Appropriate monitoring intervals depend on stability:

• If this is a newly achieved stable level: Continue monitoring every 2-3 days initially, then extend to every 1-2 weeks 1
• If long-term stable: Monitor every 1-2 months 1
• If any medication changes affecting CYP3A4: Monitor within 2-3 days 1

Common Pitfalls to Avoid

Critical considerations at this therapeutic level:

• Don't assume stability means no toxicity: Nephrotoxicity, hyperglycemia, hypertension, and neurotoxicity can occur even at therapeutic levels 1
• Don't ignore variability: High intra-patient variability (>28.8% coefficient of variation) is associated with increased rejection risk beyond the first year, even if mean levels are therapeutic 5
• Don't overlook assay interference: If the level seems inconsistent with clinical picture, consider measuring plasma tacrolimus level to rule out immunoassay interference, particularly with ACMIA method 6
• Don't forget infection prophylaxis: Pneumocystis jiroveci prophylaxis should be maintained at all therapeutic tacrolimus levels 1

Toxicity Surveillance

Even at 11.4 ng/mL, monitor for these adverse effects:

• Nephrotoxicity: Most common dose-limiting toxicity; monitor creatinine and consider dose reduction if renal dysfunction develops 1
• Metabolic effects: Hyperglycemia (10.4% incidence of new-onset diabetes), hyperkalemia, hypomagnesemia 1
• Cardiovascular: Hypertension and dyslipidemia 1
• Neurotoxicity: Tremors, paresthesias, insomnia, headache 1
• Hematologic: Bone marrow suppression requiring CBC monitoring 1