64 postmenopausal women are randomized to treatment with either effervescent and buffered alendronate or conventional alendronate -both 70mg weekly for 16 weeks to see if bone turnover is suppressed to the same extent as in the conventional formulation with the effervescent form.

Alendronate is mainstay in the treatment of osteoporosis but is often discontinued due to gastro-intestinal side-effects. These side effects are believed to be caused by a low gastric pH induced by the drug. Effervescent and buffered alendronate is a new formulation that increases gastric pH and thereby decreases risk of side effects but the clinical effect of the drug is not fully elucidated. In the present study 64 postmenopausal women with a bone mineral density T-score < -1 are randomized 1:1 to open label treatment with effervescent and buffered alendronate or conventional alendronate 70 mg weekly for 16 weeks. The primary end-point is change in the bone resorption marker "carboxy-terminal collagen crosslinks" from baseline to 16 weeks. The decrease in the two groups is compared using non-inferiority statistics. Secondary end-points include change in the bone formation marker "propeptide of type 1 procollagen", rate of change in the two bone markers and occurence of side effects.

Inclusion Criteria:

• 2 years since last menstrual bleeding
• Bone mineral density T-score < -1 at either lumbar spine or hip
• CTx > 0.42 µg/L

Exclusion Criteria:

• Ever treatment for osteoporosis
• Indication for teriparatide treatment
• Treatment with oral systemic glucocorticoids within last 12 months
• Rheumatoid arthritis
• Inflammatory bowel disease
• Untreated thyroid disease
• Primary hyperparathyroidism
• Diabetes mellitus
• eGFR < 60 mL/min
• Cancer within last 2 years except basal cell carcinoma of the skin
• Hormone therapy
• Unstable liver disease
• Contraindications for alendronate
• Major gastrointestinal disease within 12 months (eg. esophagitis, ulcer, major surgery).
• Vitamin D < 50nmol/L