Paricalcitol

Mechanism of action

◎Vitamin D receptor (nuclear receptor) in the parathyroid glandsParicalcitol

ⓘ The figure shows calcitriol, the natural active vitamin D, in the human vitamin D receptor; paricalcitol is an analogue that binds the same pocket.

Paricalcitol is a synthetic vitamin D2 analogue of calcitriol that does not need activation by the kidney. It binds the vitamin D receptor and selectively activates vitamin D-responsive pathways. In the parathyroid glands it lowers parathyroid hormone synthesis and secretion. It also raises serum calcium and phosphorus, which is why over-suppression and hypercalcaemia are the main risks.

1. Paricalcitol binds the vitamin D receptor
2. Parathyroid hormone synthesis and secretion fall
3. Calcium and phosphorus rise; levels are checked

Indications

• Prevention and treatment of secondary hyperparathyroidism of chronic kidney disease (stages 3 and 4, and stage 5 on dialysis) CKD-mineral and bone disorder (renal osteodystrophy) →

Adverse effects

Common

• Diarrhoea, nausea, vomiting
• Nasopharyngitis
• Dizziness
• High blood pressure, oedema

Contraindications

• Hypercalcaemia or vitamin D toxicity

Key interactions

Digoxin and other digitalis glycosides

Hypercalcaemia raises the risk of digitalis toxicity

Strong CYP3A inhibitors (ketoconazole)

Higher paricalcitol exposure; used with caution

Cholestyramine, mineral oil

Less paricalcitol absorbed; doses are separated

Other vitamin D products at prescription doses; aluminium-containing compounds

Added hypercalcaemia risk; aluminium overload and toxicity

What is monitored

• Serum calcium and phosphorus
• Intact PTH, especially after starting or changing the dose
• Serum creatinine (it can rise and lower estimated GFR)

Administration and safety

• Oral capsules or IV injection (often during haemodialysis); the dose is adjusted to PTH, calcium and phosphorus.
• Other prescription vitamin D products are withheld during treatment.
• Look-alike risk with calcitriol and other vitamin D analogues; the exact product is checked.

Pregnancy and breastfeeding

Human data are limited; kidney disease itself carries risks in pregnancy, and use needs a clear benefit.

Nursing care

• Check calcium, phosphorus and PTH results before giving doses.
• Teach the signs of high calcium: tiredness, confusion, loss of appetite, nausea, constipation, thirst, frequent urination.
• In patients on digoxin, watch for toxicity (nausea, visual changes, arrhythmia).
• Ask about vitamin D supplements, antacids with aluminium and other over-the-counter products.

Pharmacokinetics

Absorption

Well absorbed orally; also given IV during haemodialysis

Distribution

Almost entirely bound to plasma proteins

Metabolism

Several hepatic and non-hepatic enzymes, including CYP24, CYP3A4 and UGT1A4

Elimination

Mainly hepatobiliary, in faeces

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Connections

← Back to the class: Vitamins

Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: DailyMed - PARICALCITOL capsule (DailyMed (U.S. National Library of Medicine), 2017); DailyMed - PARICALCITOL injection (DailyMed (U.S. National Library of Medicine), 2026); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026); RCSB PDB - 1DB1: CRYSTAL STRUCTURE OF THE NUCLEAR RECEPTOR FOR VITAMIN D COMPLEXED TO VITAMIN D (RCSB Protein Data Bank, 2026).

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Representative model, for educational purposes only.