Will taking a trough level 15 minutes after the 24-hour mark for Envarsus (tacrolimus) result in an inaccurate level?

Timing of Tacrolimus (Envarsus) Trough Level Collection

Taking a trough level 15 minutes after the 24-hour mark for Envarsus (tacrolimus extended-release) will result in an inaccurate level that no longer represents a true trough concentration.

Proper Timing for Tacrolimus Trough Levels

The timing of tacrolimus trough level collection is critical for accurate therapeutic drug monitoring:

• Ideal timing: Within 0-2 hours before the next scheduled dose 1
• Acceptable range: Within 24 hours before the next scheduled dose 1
• Incorrect timing: After the next dose has been administered (invalidates the trough reading) 1

Why Timing Matters

Taking the sample 15 minutes after the next dose has several implications:

1. Pharmacokinetic impact: Tacrolimus begins absorption immediately after ingestion, with peak concentrations (Cmax) typically occurring 1.5-3.0 hours after administration 2

2. Misinterpretation risk: The level would represent the beginning of the absorption phase rather than the true trough, leading to:

   • Falsely elevated readings
   • Incorrect dose adjustments
   • Potential toxicity or undertreatment

Monitoring Recommendations

The KDIGO guidelines recommend monitoring tacrolimus using 12-hour trough (C0) levels 3, which for once-daily Envarsus means:

• Measure immediately before the next scheduled dose
• Monitor levels:
  • Every other day during the immediate post-operative period until target levels are reached
  • Whenever there is a change in medication or patient status that may affect blood levels
  • Whenever there is a decline in kidney function 3, 1

Clinical Implications

Inconsistent timing of blood collection leads to:

• Misinterpretation of results
• Inappropriate dose adjustments
• Potential for subtherapeutic or toxic levels
• Increased risk of rejection or adverse effects

Correct Procedure

If a dose is accidentally administered before the trough level is drawn:

1. Document the timing error
2. Wait until the next dosing cycle
3. Ensure proper timing of the next trough level collection (before the dose)
4. Consider consulting with the transplant team about whether interim monitoring is needed

Common Pitfalls to Avoid

• Taking the sample after medication administration
• Inconsistent timing between collections
• Failing to document the exact time of last dose and sample collection
• Not adjusting for changes in medication schedule

Following proper timing protocols for tacrolimus trough level collection is essential for accurate therapeutic drug monitoring and optimal patient outcomes.