A compound based on a hydrated Aluminum and Magnesium silicate mixture. Both substances contained in antacids do not concentrated into breast milk. Naturally occurring, the mean Magnesium concentration in the milk is 31 mg/L (range 15 – 64 mg/L) and not affected by the ingestion of Magnesium. After ingestion of antacids the Aluminum plasma levels increase from a basal-point of 7 μg/L to 55 μg/L at half-an-hour with a return to previous level 3 hours later. Although a minimal amount of Aluminum may be found in the milk, there are not shown side-effects in the infant. Mother's milk has a mean concentration of 49 μg/L of Aluminum which is much lower than the amount of 180-700 μg/L found in artificial formulas. Because of a low oral bioavailability the pass from the breast milk toward the infant's plasma is hampered, except in premature and newborn infants who may exhibit a higher intestinal absorption due to an increased permeability. Avoid chronic or excessive use. WHO Model List of Essential Medicines 2002: Aluminum hydroxide and Magnesium hydroxide are compatible with breastfeeding.