What is the recommended treatment regimen for an adult diagnosed with osteomalacia due to vitamin D deficiency?

For an adult diagnosed with osteomalacia caused by vitamin D deficiency, the recommended treatment regimen involves rapid correction of the deficiency using oral vitamin D3 (cholecalciferol) as the first-line therapy, followed by maintenance dosing to sustain adequate vitamin D levels and bone health. Typically, a loading dose of high-dose vitamin D3 is administered over 8 to 12 weeks to replenish stores, for example, 20,000 to 40,000 IU weekly or equivalent daily dosing, depending on severity and clinical judgment. After this loading phase, a maintenance dose of vitamin D3 (usually 800 to 2000 IU daily) is advised to maintain sufficient serum 25-hydroxyvitamin D concentrations. Calcium intake should also be assessed and optimized, as many patients with osteomalacia may have concurrent calcium deficiency, which can impair bone mineralization.

Intramuscular vitamin D is generally not recommended first line due to unpredictable bioavailability and slower onset of action but may be considered in cases of severe malabsorption under specialist supervision. In patients with complicating factors such as severe liver or kidney disease, specialist advice is required, and activated vitamin D metabolites (e.g., calcifediol, alfacalcidol, or calcitriol) may be necessary. Monitoring of serum calcium and phosphate is important during treatment to avoid hypercalcaemia. If symptoms persist despite correction of vitamin D deficiency, further specialist evaluation is warranted.

This approach is supported by UK clinical guidelines which emphasize oral vitamin D3 as the treatment of choice for vitamin D deficiency and osteomalacia, with a fixed loading dose regimen followed by maintenance therapy to ensure safety and efficacy. The Royal Osteoporosis Society guideline and expert reviews highlight the importance of avoiding intermittent very high doses due to fracture risk and toxicity concerns. The regimen duration is typically at least 8 to 12 weeks for loading, with ongoing maintenance thereafter. Specialist referral is recommended for complex cases or those with malabsorption or comorbidities affecting vitamin D metabolism.