Calcitriol

CLINICAL USE

Vitamin D analogue:

Promotes intestinal calcium absorption

Suppresses PTH production and release

DOSE IN NORMAL RENAL FUNCTION

Orally: 250 nanograms daily or on alternate days, increased if necessary in steps of 250 nanograms at intervals of 2–4 weeks. Usual dose 0.5–1 micrograms daily

IV: treatment of hyperparathyroidism in haemodialysis patients: initially 500 nanograms (10 nanograms/kg) 3 times a week, increased if necessary in steps of 250–500 nanograms at intervals of 2–4 weeks. Usual dose 0.5–3 micrograms 3 times a week after dialysis

PHARMACOKINETICS

Molecular weight :416.6

%Protein binding :99.9

%Excreted unchanged in urine : 7–10

Volume of distribution (L/kg) :No data

half-life – normal/ESRD (hrs) :9–10/18–20

DOSE IN RENAL IMPAIRMENT

GFR (mL/MIN)

20 to 50 : Dose as in normal renal function. Titrate to response

10 to 20 : Dose as in normal renal function. Titrate to response

<10 : Dose as in normal renal function. Titrate to response

DOSE IN PATIENTS UNDERGOING RENAL REPLACEMENT THERAPIES

CAPD :Unlikely to be dialysed. Dose as in normal renal function

HD :Not dialysed. Dose as in normal renal function

HDF/high flux :Not dialysed. Dose as in normal renal function

CAV/VVHD :Unknown dialysability. Dose as in normal renal function

IMPORTANT DRUG INTERACTIONS

Potentially hazardous interactions with other drugs

The effects of vitamin D may be reduced in patients taking barbiturates or anticonvulsants

Increased risk of hypercalcaemia if thiazides given with vitamin D

ADMINISTRATION

Reconstition

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Route

Oral, IV

Rate of Administration

Bolus

Comments

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OTHER INFORMATION

Check plasma calcium concentrations at regular intervals (initially weekly)

Dose of phosphate-binding agent may need to be modified as phosphate transport in the gut and bone may be affected

Hypercalcaemia and hypercalciuria are the major side effects, and indicate excessive dosage

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