Enteric coated preparations Antacids

Some of the didanosine preparations (e.g. chewable tablets) are formulated with antacid buffers that are intended to facilitate didanosine absorption by minimising acid-induced hydrolysis in the stomach. These preparations can therefore alter the absorption of other drugs that are affected by antacids (e.g. azole antifungals, quinolone antibacterials, tetracyclines). This interaction may be minimised by separating administration by at least 2 hours. Alternatively, the enteric-coated preparation of didanosine (gastro-resistant capsules) may be used. 

Itraconazole capsules and ketoconazole depend on stomach acidity for absorption. A raised gastric pH, caused by the antacids in the buffered didanosine formulation appears to reduce itraconazole absorption (consider, Azoles + Antacids , p.215). The didanosine itself appears to have no part to play in this interaction. The enteric-coated preparation of didanosine does not contain any antacids and therefore does not interact. 

Most of the interactions with mycophenolate mofetil and enteric-coated MPA are due to reductions in intestinal absorption. Aluminum-, magnesium-, or calcium-containing antacids decrease the peak level and overall exposure of MPA from either of the preparations.11 If a patient requires liquid antacids, they should be administered at least 4 hours before... 

The controlled study suggests that no special precautions are necessary if both drugs are given. However, the case report introduces an element of caution, especially if other drugs that may affect rifabutin pharmacokinetics are used. If indeed rifabutin absorption is affected by antacids (there appear to be no clinical data on this), then giving the drugs at least 2 hours apart, or using the enteric-coated didanosine preparation should avoid the interaction. ... 

Theoretically, enteric-coated, delayed-release preparations may possibly dissolve prematurely if they are taken at the same time as antacids. This has been seen with some preparations, but not others. Release characteristics are likely to depend on the specific coating, and the manufacturers advice should be followed. 

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