Narrow therapeutic index: large inter- and intra-patient PK variability — trough-level guided dosing is mandatory, never dose by weight alone beyond the induction period.
Mechanism & place in therapy
Tacrolimus (Prograf — BID; Advagraf / Envarsus — OD extended-release)
- Calcineurin inhibitor → blocks calcineurin-mediated IL-2 gene transcription → suppresses T-cell activation
- First-line CNI for maintenance immunosuppression in kidney transplant recipients (KTR), superior to cyclosporine for rejection prevention
Standard maintenance regimen: tacrolimus + antiproliferative agent (mycophenolate mofetil — CellCept; or mycophenolic acid — Myfortic) ± corticosteroid.
Typical maintenance regimen
Induction (basiliximab / ATG per immunologic risk)
↓
Tacrolimus + MMF/MPA ± prednisolone — start day 0–1
↓ titrate to trough target
0–4 wkHighest rejection risk — upper target range
1–12 moTaper toward mid-range as risk falls
>12 mo, stableLowest effective level — minimize toxicity
How to monitor
Trough level (C0)
12-hour trough, drawn immediately before next dose (KDIGO 2C)
- Do not use random or peak levels for dose titration
- Whole-blood level (not plasma/serum) — confirm lab method matches assay used for reported targets
Frequency
Inpatient / early post-op
3× per week
- Recheck with any dose change, formulation switch (e.g., Prograf ↔ Advagraf), or new interacting drug
- Recheck with unexplained graft dysfunction (rising creatinine — distinguishes nephrotoxicity vs. rejection)
Outpatient, stable
Weekly → biweekly → monthly, then per transplant clinic protocol as level and renal function stabilize
What to trend alongside C0
Companion labs
- Serum creatinine / eGFR — differentiate CNI nephrotoxicity from rejection
- Potassium, magnesium (tacrolimus causes hyperkalemia + hypomagnesemia)
- Fasting glucose (post-transplant diabetes mellitus risk)
- Blood pressure
Target trough (C0) by time post-transplant
| Period | Target C0 | Rationale |
|---|---|---|
| 0–4 wk | 6–10 ng/mL | Highest acute rejection risk |
| 1–3 mo | 6–8 ng/mL | Risk declining, still on triple therapy |
| 3–12 mo | 5–8 ng/mL | Taper as graft stabilizes |
| >12 mo, stable/low-risk | 4–6 ng/mL | Minimize nephrotoxicity, infection, malignancy |
Ranges vary by center protocol, induction agent, and immunologic risk (HLA mismatch, DSA status). C0 <5 ng/mL associated with higher biopsy-proven rejection and de novo DSA formation; C0 persistently >10 ng/mL raises nephrotoxicity/infection/malignancy risk. Target the lowest level that prevents rejection, individualized to risk.
Confirm against local protocol: if PSU transplant surgery/nephrology unit has an institutional target-level protocol, that supersedes these general ranges.
Key toxicities
Nephrotoxicity
- Dose-dependent afferent arteriolar vasoconstriction — rising creatinine may reflect toxicity rather than rejection; biopsy if uncertain
Metabolic / other
- New-onset diabetes after transplant (NODAT), hyperkalemia, hypomagnesemia, hypertension, tremor, neurotoxicity (higher with Advagraf per some VEP data)
Major interactions (check before every new prescription)
CYP3A4/5 interactions
- ↑ levels (risk of toxicity): azole antifungals (fluconazole, voriconazole), clarithromycin/erythromycin, diltiazem, verapamil, protease inhibitors
- ↓ levels (risk of rejection): rifampin, phenytoin, carbamazepine, St. John's wort
Recheck trough level within days of starting/stopping any interacting drug.