In chronic renal failure, the inability to produce calcitriol (1,25-dihydroxyvitamin D) leads to renal osteodystrophy. Calcitriol deficiency results in low calcium and high phosphate levels in the blood, stimulating parathyroid hormone secretion and causing demineralization of bones. To treat this, vitamin D must be accompanied by phosphate reduction through a low-phosphate diet and phosphate binders, as high phosphate levels can lead to soft tissue calcification when combined with low calcium levels.
2. IN CHRONIC RENAL FAILURE, A CHAIN OF
EVENTS LEADS TO RENAL OSTEODYSTROPHY
THE RENAL FAILURE RESULTS IN THE
INABILITY TO PRODUCE 1,25-
DIHYDROXYCHOLECALCIFEROL (CALCITROL)
3. VITAMIN D IS CONSIDERED AS A PROVITAMIN
THAN VITAMIN
CHOLECALCIFEROL (D30 IS PRODUCED FROM
SUNLIGHT IN SKIN
THUS A LONG EXPOSURE OF SKIN IN
SUNLIGHT DOESNOT REQUIRE DIETARY
INTAKE
CHOLECALCIFEROL IS MAINLY METABOLIZED
IN LIVER WHERE 25-
HYDROXYCHOLECALCIFEROL IS FORMED
4. 25-HYDROXYCHOLECALCIFEROL IS
CONVERTED TO BIOLOGICALLY ACTIVE 1-
α,25DIHYDROXYCHOLECALCIFEROL
THIS IS CALLED CALCITROL
THIS IS USUALLY DONE BY AN ENZYME 25-
HYDROXYVITAMIN D-1-α HYDROXYLASE
5. KIDNEYS APPEAR AS A MAJOR SOURCE OF 1-
α25 DIHYDROXYCHOLECALCIFEROL
ALSO SOME OF THE MAJOR TISSUES
INCLUDING BREAST,PROSTRATE,COLON
6. THE REDUCTION IN LEVEL OF CALCIUM IN
SERUM RESULTS IN THE INCREASED LEVEL OF
PHOSPHATE
RESULTING IN THE CONDITION OF
HYPERPHOSPHATEMIA
THE SERUM PHOSPHATE LEVELS ARE OFTEN
HIGH ENOUGH TO METASTISE CALCIUM i.e
CALCIFICATION OF SOFT TISSUES
IT TENDS TO LOWER SERUM CALCIUM LEVELS
7.
8. FURTHER HYPERPHOSPHATEMIA AND
HYPOCALCEMIA STIMULATE PARATHYROID
HORMONE SECRETION
THIS CONDITION LEADS TO
DEMINERALIZATION OF BONES
9.
10.
11. ADMINISTRATION OF VITAMIN D IS NOT
SUFFICIENT BECAUSE OF COMBINATION OF
HYPERPHOSPHATEMIA AND HYPOCALCEMIA
IT LEADS TO EXTENSIVE METASTASTIC
CALCIFICATION
THE HIGH DOSES OF VITAMIN D MUST BE
ACCOMPANIED BY PHOSPHATE REDUCTION
BUT IT IS DIFFICULT TO TEDUCE DIRECTLY
PHOSPHATE BECAUSE MOST PROTEIN
SOURCES ARE HIGH IN CALCIUM
12. IN THIS REGARD VEGETABLE PROTEINS IS
BETTER CHOICE THAN ANIMAL PROTEIN
THIS IS BECAUSE VEGETABLE PROTEINS IS IN
THE FORM OF PHYTATES
AND ARE UNAVAILABLE FOR ABSORPTION
IT IS NECESSARY TO AVOID PROCESSED FAT
BECAUSE OF ADDING OF PHOSPHATES
CALCIUM ACETATE AND A CATIONIC
POLYMER CALLED SEVELAMER
HYDROCHLORIDE ARE MOST COMMONLY
USED PHOSPHATE BINDER AT PRESENT
13. ORALLY ADMINISTERED 1,25-(OH)2 D IS
EFFECTIVE AT STIMULATING CALCIUM
ABSORPTION IN THE MUCOSA
BUT IT DOESNOT SIGNIFICANTLY ENTER
PERIPHERAL CIRCULATION
THUS IN SEVERE HYPERPARATHYROIDISM
INTRAVENOUS 1,25(OH)2 D IS REQUIRED
14. DEFICIENCY OF VITAMIN D ALSO LEADS TO
◦ RICKETS-IN GROWING CHILDREN
◦ OSTEOMALACIA-IN ADULTS