Calcineurin Inhibitor
Calcineurin Inhibitor
Calcineurin Inhibitors (CNIs)
Calcineurin inhibitors are potent immunosuppressive agents that block T-cell activation by inhibiting the phosphatase calcineurin, thereby preventing transcription of IL-2 and other cytokines.
1️⃣ Core Drugs
- Cyclosporine
- Tacrolimus
(Both are cornerstone drugs in solid organ transplantation.)
Mechanism of Action (High-Yield Immunology)
Normal pathway:
- T-cell receptor activation → ↑ intracellular Ca²⁺
- Ca²⁺ binds calmodulin → activates calcineurin
- Calcineurin dephosphorylates NFAT
- NFAT enters nucleus → ↑ IL-2 transcription → T-cell proliferation
CNIs block calcineurin → no NFAT activation → ↓ IL-2 → ↓ clonal T-cell expansion
Drug-Specific Binding Proteins
| Drug | Binds to | Complex Inhibits |
|---|---|---|
| Cyclosporine | Cyclophilin | Calcineurin |
| Tacrolimus | FKBP-12 | Calcineurin |
Clinical Uses
1. Transplant Medicine
- Kidney transplant
- Liver transplant
- Heart transplant
- Lung transplant
2. Autoimmune Disorders
- Psoriasis
- Rheumatoid arthritis
- Atopic dermatitis (topical tacrolimus)
- Steroid-resistant nephrotic syndrome
Adverse Effects (Exam Gold)
🔴 Nephrotoxicity (Dose-limiting)
- Afferent arteriolar vasoconstriction
- Chronic interstitial fibrosis
⚡ Neurotoxicity
- Tremors (more common with tacrolimus)
- Seizures
- Posterior reversible encephalopathy syndrome (PRES)
🧂 Hypertension
- Due to renal vasoconstriction + RAAS activation
🧪 Metabolic Effects
- Hyperkalemia
- Hypomagnesemia
- Hyperuricemia
🩸 Diabetes Mellitus
- More common with tacrolimus
💇 Cosmetic Effects
- Cyclosporine → hirsutism + gingival hyperplasia
- Tacrolimus → alopecia
Drug Interactions (CYP3A4 Metabolism)
Both drugs are metabolized by CYP3A4.
Increase CNI levels:
- Macrolides
- Azoles
- Diltiazem
- Grapefruit juice
Decrease CNI levels:
- Rifampicin
- Phenytoin
- Carbamazepine
Monitoring
- Trough levels (narrow therapeutic window)
- Serum creatinine
- Blood pressure
- Blood glucose
- Electrolytes
CNI vs mTOR Inhibitors (Conceptual Contrast)
| Feature | Calcineurin Inhibitors | mTOR inhibitors |
|---|---|---|
| Block | IL-2 transcription | IL-2 response |
| Example | Cyclosporine, Tacrolimus | Sirolimus |
| Nephrotoxicity | Yes | Minimal |
Classic Exam Comparisons
| Feature | Cyclosporine | Tacrolimus |
|---|---|---|
| Potency | Less | More |
| Diabetes | Less common | More common |
| Cosmetic effects | Hirsutism | Alopecia |
| Neurotoxicity | Moderate | Higher |
One-Liner Pearls (SS/DM level)
- Afferent arteriolar vasoconstriction = hallmark toxicity
- Tacrolimus causes more diabetes; cyclosporine causes more cosmetic changes.
- Both increase risk of PTLD (EBV-driven).
- Both are contraindicated with strong CYP3A4 inhibitors without dose adjustment.
1. Calcineurin inhibition directly prevents activation of:
A. STAT5
B. NFAT
C. mTORC1
D. JAK3
Calcineurin dephosphorylates NFAT → nuclear IL-2 transcription.
2. Tacrolimus-FKBP complex inhibits:
A. mTOR
B. IL-2 receptor
C. Calcineurin phosphatase
D. CD40L
Tacrolimus binds FKBP-12 → complex inhibits calcineurin.
3. Acute nephrotoxicity is primarily due to:
A. Tubular necrosis
B. Immune complex deposition
C. Glomerular thrombosis
D. Afferent arteriolar vasoconstriction
Reversible vasoconstriction reduces renal blood flow.
4. Chronic CNI nephropathy shows:
A. Interstitial fibrosis with arteriolar hyalinosis
B. Crescent formation
C. Podocyte effacement
D. Amyloid deposition
Striped fibrosis + arteriolar hyaline thickening are classic.
5. Tacrolimus has higher incidence of:
A. Hirsutism
B. Post-transplant diabetes
C. Gingival hyperplasia
D. Hyperlipidemia
Tacrolimus is more diabetogenic than cyclosporine.
6. Cyclosporine binds:
A. FKBP-12
B. mTOR
C. Cyclophilin
D. Calmodulin
Cyclosporine-cyclophilin complex inhibits calcineurin.
7. Posterior reversible encephalopathy syndrome is linked to:
A. Azathioprine
B. Mycophenolate
C. Sirolimus
D. Calcineurin inhibitors
PRES is a classic neurotoxicity of CNIs.
8. Drug that increases CNI levels:
A. Clarithromycin
B. Rifampicin
C. Phenytoin
D. Carbamazepine
Macrolides inhibit CYP3A4 → increase levels.
9. Common electrolyte abnormality:
A. Hypermagnesemia
B. Hypomagnesemia
C. Hypokalemia
D. Hypernatremia
Renal magnesium wasting is common.
10. Both drugs are metabolized primarily by:
A. CYP2D6
B. Renal excretion unchanged
C. CYP3A4
D. Glucuronidation
Major CYP3A4 drug-drug interactions occur.
11. Primary cytokine suppressed:
A. IL-4
B. TNF-α
C. IL-10
D. IL-2
IL-2 transcription is directly reduced.
12. Compared to mTOR inhibitors, CNIs:
A. Reduce IL-2 transcription
B. Block IL-2 receptor
C. Inhibit cell cycle at G1
D. Cause less nephrotoxicity
mTOR inhibitors block IL-2 response; CNIs block transcription.
13. PTLD risk is associated with:
A. Direct mutagenesis
B. EBV-driven proliferation
C. UV radiation
D. Myelosuppression
Immunosuppression predisposes to EBV-mediated lymphomas.
14. Hypertension mechanism:
A. Volume depletion
B. β-agonism
C. Renal vasoconstriction + RAAS activation
D. NO excess
Renal vasoconstriction activates RAAS → HTN.
15. Drug decreasing CNI level:
A. Ketoconazole
B. Diltiazem
C. Erythromycin
D. Rifampicin
Rifampicin induces CYP3A4.
16. Cosmetic effect typical of cyclosporine:
A. Hirsutism
B. Alopecia
C. Photosensitivity
D. Vitiligo
Cyclosporine causes hirsutism + gingival hyperplasia.
17. Monitoring essential due to:
A. Long half-life
B. Narrow therapeutic index
C. High protein binding
D. Low bioavailability
Small therapeutic window → trough monitoring required.
18. Target cell primarily suppressed:
A. B cells
B. Neutrophils
C. T lymphocytes
D. NK cells
CNIs suppress T-cell activation.
19. Tacrolimus compared to cyclosporine is:
A. Less potent
B. Less diabetogenic
C. More cosmetic adverse effects
D. More potent immunosuppressant
Tacrolimus is more potent and more diabetogenic.
20. Acute CNI nephrotoxicity is reversible if:
A. Dose reduced early
B. Dialysis started
C. Steroids added
D. ACE inhibitor started
Early dose reduction reverses vasoconstrictive injury.
