Coadministration of efavirenz with medicinal products that alter gastric pH would not be expected to affect efavirenz absorption. Coadministration of an antacid containing aluminium hydroxide-magnesium hydroxide-simethicone (Maalox, 30 ml single dose) and efavirenz (400 mg single dose) did not alter the absorption of efavirenz. Coadministration with antacids containing calcium carbonate has not been studied. No dosage adjustment is recommended when efavirenz is given with antacids.