Calcitriol is one of the most important activated metabolites of vitamin D3, which can promote the absorption of calcium by the small intestinal mucosa and the reabsorption of phosphorus by the renal tubules, increase the concentration of blood calcium and blood phosphorus, cooperate with parathyroid hormone and calcitonin, promote the release of calcium phosphate from old bones, and maintain and regulate the normal concentration of blood calcium and blood phosphorus. Calcitriol can also promote calcium deposition in the new bone formation site, so that citrate is deposited in bone, promote bone calcification and osteoblast function and bone-like tissue maturation, mainly suitable for postmenopausal and elderly osteoporosis, renal osteodystrophy, hypoparathyroidism, vitamin D-dependent rickets, and hypophosphatemic vitamin D-resistant rickets.
When calcitriol is started**, the lowest dose should be used, and the dose should be increased while monitoring the serum calcium level, and after the optimal daily dose is determined, the serum calcium level should be rechecked on a monthly basis, and if the serum calcium is exceeded, the dose should be reduced or completely discontinued** until the serum calcium is normal. During the period of elevated calcium, serum calcium and phosphorus levels should be measured daily, and after normal calcium, the daily dose of calcitriol should be less than 025 mcg. The prerequisite for the best efficacy of calcitriol is an adequate but not excessive intake of calcium (**total daily calcium intake of about 800 mg, including from food and drugs**, should not exceed 1000 mg).
Specifically, for postmenopausal and senile osteoporosis patients, the recommended dose of calcitriol is 025 micrograms, 2 times a day, after taking the drug, the serum calcium and serum creatinine concentrations were monitored at the 4th week, 3rd month, and 6th month, respectively, and every 6 months thereafter. For patients with renal osteodystrophy, the daily dose of calcitriol in the initial phase is 025 mcg. Patients with normal or slightly decreased serum calcium are 0 every other day25 mcg. If there is no significant improvement in biochemical indexes and condition within 2-4 weeks, the dose will be increased by 0 every 2-4 Sundays25 (blood calcium is measured at least twice a week during this period). The optimal dosage for most patients is 05-1.0 mcg. For patients with hypoparathyroidism and rickets, the recommended starting dose is 025 mcg, morning wear. If there is no significant improvement in biochemical markers and condition, the dose is increased every 2-4 weeks. During this period, serum calcium is measured at least twice a week.
Small doses alone (0.).5 micrograms a day) calcitriol generally has no adverse reactions, long-term high-dose use or combination with calcium can cause hypercalcemia and hypercalciuria, which can cause systemic vascular calcification, renal calcium precipitation and other soft tissue calcification, resulting in hypertension and renal failure. If there are symptoms such as nausea, vomiting, lack of appetite, extreme thirst, polyuria, constipation and diarrhea, irritability, depression and other symptoms during the course of medication, you should be alert to vitamin D poisoning.
*At the beginning, calcium supplementation is necessary, and attention should be paid to measuring blood calcium, blood urea nitrogen, creatinine and urine calcium, and urine creatinine during the course of medication.
Patients with hypoparathyroidism occasionally have poor absorption and require a higher dose.
It is used in young patients and is limited to young adult idiopathic osteoporosis (unexplained osteoporosis) and osteoporosis caused by glucocorticoid excess.
Arteriosclerosis, cardiac insufficiency, hypercholesterolemia, and hyperphosphatemia should be used with caution.
Under the skin of the human body, there are many raw materials for the synthesis of vitamin D3 (vitamin D3), which are converted into vitamin D3 under the irradiation of sunlight (ultraviolet rays), and vitamin D3 enters the bloodstream, where it is first transported to the liver, and is converted into 25-hydroxyvitamin D3 by 25-hydroxylase in the liver, which is transported to the kidneys with blood circulation, and is converted into 1,25-dihydroxyvitamin D3 by the 1-hydroxylase enzyme in the kidneys, that is, calcitriol, and finally absorbed and utilized by the body.
Alfacalciferol is a prodrug, also known as 1-hydroxyvitamin D3, which is a synthetic active vitamin D, which can be rapidly converted into calcitriol by 25-hydroxylase and osteoblasts in the liver after taking it, so the clinical efficacy of alfacalciferol is basically the same as that of calcitriol, because renal transformation is not required, so alfacalciferol is especially suitable for the elderly and patients with reduced renal function.