This is a multi-centre, double blind, randomised, placebo controlled, parallel group, phase 4 pilot study investigating colecalciferol (vitamin D3) as an add-on treatment to subcutaneously administered interferon-beta-1b in relapsing-remitting multiple sclerosis patients.

Inclusion Criteria:

• age 18 to 55 years
• remitting-relapsing multiple sclerosis according to McDonald criteria who fulfill the reimbursement criteria for interferon-beta and have used interferon-beta-1b for at least one month
• EDSS (expanded disability statsu scale) ≤ 5
• no neutralising antibodies to INFB as measured by indirect MxA test
• prepared and considered to follow the protocol
• using appropriate contraceptive methods (women of childbearing potential)
• has given informed consent

Exclusion Criteria:

• serum calcium >2.6 mmol/L
• serum 25(OH)D2 (kalsidiol) > 85 nmol/L
• presence of primary hyperparathyroidism (serum intact PTH, parathyroid hormone)>65 ng/L)
• pregnancy or unwillingness to use contraception
• alcohol or drug abuse
• use of glucocorticoid treatment other than intravenous methylprednisolone for treatment of relapses
• current use of other immunomodulatory therapy than interferon-beta-1b
• known allergy to cholecalciferol or arachis oil (peanuts)
• therapy with digitalis, calcitonin or active vitamin D3 analogues during the previous 12 months or multivitamins containing vitamin D during previous two weeks preceding study entry
• any condition predisposing to hypercalcaemia (such as any type of cancer)
• sarcoidosis
• nephrolithiasis or renal insufficiency, serum creatinine above 1.5 times the normal upper reference limit
• significant hypertension (Blood Pressure <180/110 mmHg)
• hyperthyroidism, or hypothyroidism in the year before the study began
• a history of nephrolithiasis during the previous five years
• cardiac insufficiency or significant cardiac dysrhythmia
• unstable or advanced ischaemic heart disease
• has suffered a major depression