Paricalcitol

Paricalcitol is indicated in adults for the prevention and treatment of secondary hyperparathyroidism in patients with chronic kidney disease Stage 5 who are undergoing haemodialysis.

Posology

Adults

1) Initial dose should be calculated based on baseline parathyroid hormone (PTH) levels:

The initial dose of paricalcitol is based on the following formula:

and administered as an intravenous (IV) bolus dose no more frequently then every other day at any time during dialysis.

The maximum dose safely administered in clinical studies was as high as 40 micrograms.

2) Titration dose:

The currently accepted target range for PTH levels in end-stage renal failure subjects undergoing dialysis is no more than 1.5 to 3 times the non-uremic upper limit of normal, 15.9 to 31.8 pmol/l (150-300 pg/ml), for intact PTH. Close monitoring and individual dose titration are necessary to reach appropriate physiological endpoints. If hypercalcaemia or a persistently elevated corrected Ca x P product greater than 5.2 mmol²/l² (65 mg²/dl²) is noted, the dosage should be reduced or interrupted until these parameters are normalised. Then, paricalcitol administration should be reinitiated at a lower dose. Doses may need to be decreased as the PTH levels decrease in response to therapy.

The following table is a suggested approach for dose titration:

Once dosage has been established, serum calcium and phosphate should be measured at least monthly. Serum intact PTH measurements are recommended every three months. During dose adjustment with paricalcitol, laboratory tests may be required more frequently.

Hepatic impairment

Unbound concentrations of paricalcitol in patients with mild to moderate hepatic impairment are similar to healthy subjects and dose adjustment is not necessary in this patient population. There is no experience in patients with severe hepatic impairment.

Paediatric population (0-18 years)

Elderly (>65years)

There is a limited amount of experience with patients 65 years of age or over receiving paricalcitol in the phase III studies. In these studies, no overall differences in efficacy or safety were observed between patients 65 years or older and younger patients.

Method of administration

Zemplar solution for injection is administered via haemodialysis access.

Vitamin D toxicity

Hypercalcaemia

Over suppression of parathyroid hormone may result in elevations of serum calcium levels and may lead to metabolic bone disease. Patient monitoring and individualised dose titration is required to reach appropriate physiological endpoints.

If clinically significant hypercalcaemia develops, and the patient is receiving a calcium-based phosphate binder, the dose of the calcium-based phosphate binder should be reduced or interrupted.

Chronic hypercalcaemia may be associated with generalised vascular calcification and other soft-tissue calcification.

Phosphate or vitamin D-related medicinal products should not be taken concomitantly with paricalcitol due to an increased risk of hypercalcaemia and Ca x P product elevation.

Digitalis toxicity is potentiated by hypercalcaemia of any cause, so caution should be applied when digitalis is prescribed concomitantly with paricalcitol.

Caution should be exercised if co-administering paricalcitol with ketoconazole.

Warning for excipients

This medicinal product contains 20% v/v of ethanol (alcohol). Each dose may contain up to 1.3g ethanol which may be harmful for those suffering from alcoholism (refer to sections 2 and 4.2). To be taken into account in pregnant or breast-feeding women, children and high risk groups such as patients with liver disease or epilepsy.

Dizziness may occur following administration of paricalcitol, which may have a minor influence on the ability to drive and use machines.

Summary of the safety profile

Approximately 600 patients were treated with paricalcitol in Phase II/III/IV clinical trials. Overall, 6% of the paricalcitol treated patients reported adverse reactions.

The most common adverse reaction associated with paricalcitol therapy was hypercalcaemia, occurring in 4.7% of patients. Hypercalcaemia is dependent on the level of PTH oversuppression and can be minimised by proper dose titration.

Tabulated list of adverse reactions

Adverse events at least possibly related to paricalcitol, both clinical and laboratory are displayed by MedDRA System Organ Class, Adverse Reaction and frequency. The following frequency groupings are used: Very common ( > 1/10); common (> 1/100, <1/10); uncommon (> 1/1,000, to <1/100); rare (> 1/10,000, <1/1,000); very rare (<1/10000), not known (cannot be estimated from the available data).

Frequencies for adverse reactions from postmarketing experience cannot be estimated and have been reported as “Not known.”

Reporting of suspected adverse reactions

Reporting of suspected adverse reactions after authorisation of the medicinal product is important. It allows continued monitoring of the benefit/risk balance of the medicinal product. Healthcare professionals are asked to report any suspected adverse reactions via the Yellow Card Scheme:

Website: www.mhra.gov.uk/yellowcard or search for MHRA Yellow Card in the Google Play or Apple App Store.

No case of overdose has been reported.

Overdosage of paricalcitol may lead to hypercalcaemia, hypercalciuria, hyperphosphatemia, and over suppression of PTH.

In the event of an overdose, signs and symptoms of hypercalcaemia (serum calcium levels) should be monitored and reported to a physician. Treatment should be initiated as appropriate.

Paricalcitol is not significantly removed by dialysis. Treatment of patients with clinically significant hypercalcaemia consists of immediate dose reduction or interruption of paricalcitol therapy and includes a low calcium diet, withdrawal of calcium supplements, patient mobilisation, attention to fluid and electrolyte imbalances, assessment of electrocardiographic abnormalities (critical in patients receiving digitalis), and haemodialysis or peritoneal dialysis against a calcium-free dialysate, as warranted.

When serum calcium levels have returned to within normal limits, paricalcitol may be reinitiated at a lower dose. If persistent and markedly elevated serum calcium levels occur, there are a variety of therapeutic alternatives that may be considered. These include the use of drugs such as phosphates and corticosteroids as well as measures to induce diuresis.

Zemplar solution for injection contains 30% v/v of propylene glycol as an excipient. Isolated cases of Central Nervous System depression, haemolysis and lactic acidosis have been reported as toxic effect associated with propylene glycol administration at high doses. Although they are not expected to be found with Zemplar administration as propylene glycol is eliminated during the dialysis process, the risk of toxic effect in overdosing situations has to be taken into account.

Pharmaco-therapeutic group: Anti-parathyroid agents , ATC code: H05BX02.

Mechanism of action

Paricalcitol is a synthetic, biologically active vitamin D analogue of calcitriol with modifications to the side chain (D₂) and the A (19-nor) ring. Unlike calcitriol, paricalcitol is a selective vitamin D receptor (VDR) activator. Paricalcitol selectively upregulates the VDR in the parathyroid glands without increasing VDR in the intestine and is less active on bone resorption. Paricalcitol also upregulates the calcium sensing receptor (CaSR) in the parathyroid glands. As a result, paricalcitol reduces parathyroid hormone (PTH) levels by inhibiting parathyroid proliferation and decreasing PTH synthesis and secretion, with minimal impact on calcium and phosphorus levels, and can act directly on bone cells to maintain bone volume and improve mineralization surfaces. Correcting abnormal PTH levels, with normalization of calcium and phosphorus homeostasis, may prevent or treat the metabolic bone disease associated with chronic kidney disease.

Paediatric population

The safety and effectiveness of paricalcitol injection were examined in a 12-week randomised, double-blind, placebo-controlled study of 29 pediatric patients, aged 5-19 years, with end-stage renal disease on hemodialysis. The six youngest paricalcitol -treated patients in the study were 5 - 12 years old. The initial dose of paricalcitol was 0.04 microgram/kg 3 times per week, based on baseline iPTH level of less than 500 pg/ml, or 0.08 microgram/kg 3 times a week based on baseline iPTH level of > 500 pg/ml, respectively. The dose of paricalcitol was adjusted in 0.04 microgram/kg increments based on the levels of serum iPTH, calcium, and Ca x P. 67% of the paricalcitol -treated patients and 14% placebo-treated patients completed the trial. 60% of the subjects in the paricalcitol group had 2 consecutive 30% decreases from baseline iPTH compared with 21% patients in the placebo group. 71% of the placebo patients were discontinued due to excessive elevations in iPTH levels. No patients in either the paricalcitol group or placebo group developed hypercalcaemia. No data are available for patients under the age of 5.

Distribution

The pharmacokinetics of paricalcitol have been studied in patients with chronic renal failure (CRF) requiring haemodialysis. Paricalcitol is administered as an intravenous bolus injection. Within two hours after administering doses ranging from 0.04 to 0.24 microgram/kg, concentrations of paricalcitol decreased rapidly; thereafter, concentrations of paricalcitol declined log-linearly with a mean half-life of about 15 hours. No accumulation of paricalcitol was observed with multiple dosing. In vitro plasma protein binding of paricalcitol was extensive (>99.9%) and nonsaturable over the concentration range of 1 to 100 ng/ml.

Biotransformation

Several unknown metabolites were detected in both the urine and faeces, with no detectable paricalcitol in the urine. These metabolites have not been characterised and have not been identified. Together, these metabolites contributed 51% of the urinary radioactivity and 59% of the faecal radioactivity.

Elimination

In healthy subjects, a study was conducted with a single 0.16 microgram/kg intravenous bolus dose of ³H-paricalcitol (n=4), plasma radioactivity was attributed to parent substance. Paricalcitol was eliminated primarily by hepatobiliary excretion, as 74% of the radioactive dose was recovered in faeces and only 16% was found in urine.

Special populations

Gender, race and age

No age or gender related pharmacokinetic differences have been observed in adult patients studied. Pharmacokinetic differences due to race have not been identified.

Hepatic impairment

Unbound concentrations of paricalcitol in patients with mild to moderate hepatic impairment is similar to healthy subjects and dose adjustment is not necessary in this patient population. There is no experience in patients with severe hepatic impairment.

Salient findings in the repeat dose toxicology studies in rodents and dogs were generally attributed to paricalcitol's calcaemic activity. Effects not clearly related to hypercalcaemia included decreased white blood cell counts and thymic atrophy in dogs, and altered APTT values (increased in dogs, decreased in rats). WBC changes were not observed in clinical trials of paricalcitol.

Paricalcitol did not affect fertility in male or female rats and there was no evidence of teratogenic activity in rats or rabbits. High doses of other vitamin D preparations applied during pregnancy in animals lead to teratogenesis. Paricalcitol was shown to affect foetal viability, as well as to promote a significant increase of peri-natal and post-natal mortality of newborn rats, when administered at maternally toxic doses.

Paricalcitol did not exhibit genotoxic potential in a set of in-vitro and in-vivo genotoxicity assays

Carcinogenicity studies in rodents did not indicate any special risks for human use.

Doses administered and/or systemic exposures to paricalcitol were slightly higher than therapeutic doses/systemic exposures.

In the absence of compatibility studies, this medicinal product must not be mixed with other medicinal products.

Propylene glycol interacts with heparin and neutralises its effect. Zemplar solution for injection contains propylene glycol as an excipient and should be administered through a different injection port than heparin.

Parenteral medicinal products should be inspected visually for particulate matter and discoloration prior to administration. The solution is clear and colourless.

For single use only.

Any unused medicinal product or waste should be disposed of in accordance with local requirements.