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.

Calcineurin Inhibitor