Cooper and Gittoes hardly mention the therapeutic use of oral calcium.1 At least two points should be considered. Firstly, hypoparathyroidism with mild and chronic hypocalcaemia can be treated with oral calcium alone.2 Secondly, different calcium salts do not have the same bioavailability.
Calcium carbonate is the cheapest and most frequently supplied oral calcium salt. It is used in most calcium plus vitamin D supplements. However, its absorption is greatly reduced in patients with achlorhydria, unless taken with meals.3 Achlorhydric and older patients, who often have hypochlorhydria, should be advised to take calcium carbonate with meals or to take calcium citrate (at any time of the day). The second option , however, costs about 50% more.
The absorption of calcium carbonate is also impaired in fasting patients taking proton pump inhibitors.4 To my knowledge, its absorption with meals has not been studied in these patients. Most experts therefore recommend that patients on these drugs take calcium citrate instead.
Competing interests: None declared.
References
- 1.Cooper MS, Gittoes NJ. Diagnosis and management of hypocalcaemia. BMJ 2008;336:1298-302. (7 June.) [DOI] [PMC free article] [PubMed] [Google Scholar]
- 2.Bushinsky DA, Monk RD. Electrolyte quintet: calcium. Lancet 1998;352:306-11. Erratum in: Lancet 2002;359:266. [DOI] [PubMed] [Google Scholar]
- 3.Recker RR. Calcium absorption and achlorhydria. N Engl J Med 1985;313:70-3. [DOI] [PubMed] [Google Scholar]
- 4.O’Connell MB, Madden DM, Murray AM, Heaney RP, Kerzner LJ. Effects of proton pump inhibitors on calcium carbonate absorption in women: a randomized crossover trial. Am J Med 2005;118:778-81. [DOI] [PubMed] [Google Scholar]