Interaction between Calcium carbonate and Raltegravir
Major Absorption

ID DDInter271 and DDInter1563
Interaction Coadministration with aluminum-, magnesium-, and/or calcium-containing antacids may reduce the oral bioavailability of raltegravir. The proposed mechanism is chelation of raltegravir by polyvalent cations, but changes in solubility and lipophilicity of raltegravir related to pH increases may also contribute.
Management Concomitant use of raltegravir with aluminum- and/or magnesium-containing antacids should generally be avoided, even if administration is staggered. Antacids containing calcium carbonate should not be used with once-daily raltegravir (HD formulation), but may be used without dose adjustment for other raltegravir products.
References
Alternative for Calcium carbonate A12A

A11G
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Alternative for Raltegravir J05A
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Potential Metabolism Interactions

Substrate-Substrate Interaction:If more than one drug is metabolized by the same CYP, it is possible that its metabolism is inhibited because of the competition between the drugs. That means, it can be useful to lower the dosage of the drugs in the drug-cocktail because they remain longer in the organism than in monotherapy.
Inhibitor-Inhibitor Interaction:Combining two or more inhibitors of one CYP, should be compensated by lowering the dosage of these drugs because the metabolism is reduced and the drugs remain longer in the organism than in monotherapy. Not adapting the dosage bears the risk of even more side effects.
Inhibitor-Substrate Interaction:Combining drugs that have inhibitory effect and are substrates of one particular CYP, should be compensated by lowering the dosage. They rest longer in the organism than in monotherapy. Not adapting the dosage bears the risk of even more side effects.