In a small study magnesium trisilicate reduced the AUC of
chloroquine by 18.2%. Related
in vitro studies found that the absorption of
chloroquine was decreased as follows: magnesium trisilicate 31.3%,
calcium carbonate 52% and gerdiga 36.1%. Gerdiga is a clay containing hydrated silicates with sodium and potassium carbonates and bicarbonates. It is used as an antacid and is similar to attapulgite. Hydroxychloroquine is predicted to interact like
chloroquine.
The
clinical significance of this reduction is unclear, but one way to minimise any possible effect on
chloroquine absorption is to separate the dosages by at least 2 to 3 hours. Hydroxychloroquine should be given 4 hours before or after
antacids.