Availability of magnesium from various commercially available oral preparations in a variety of dosage forms: comparative in vitro study.

The relative dialysability of magnesium in a number of different inorganic and organic magnesium-containing compounds from ten commercially available products was investigated using an in vitro method. Reference values were provided by tests carried out in parallel using comparable quantities of pure magnesium compounds, as contained in the products. The results demonstrated that the excipients generally had a positive effect on the relative availability of magnesium. Furthermore, the dialysed magnesium levels were lower in capsules and coated tablets than in granulates, chewable tablets, and effervescent tablets. It can be concluded that substances such as citric acid, lactose, and sucrose have a positive effect, whereas gel-based excipients and coatings have a negative effect on the availability of magnesium.