Drug Interactions between aluminum hydroxide / calcium carbonate / magnesium hydroxide / simethicone and riociguat

GENERALLY AVOID: The concomitant administration of aluminum-containing products (e.g., antacids and phosphate binders) and citrates may significantly increase serum aluminum concentrations, resulting in toxicity. Citrates or citric acid are contained in numerous soft drinks, citrus fruits, juices, and effervescent and dispersible drug formulations. Citrates enhance the gastrointestinal absorption of aluminum by an unknown mechanism, which may involve the formation of a soluble aluminum-citrate complex. Various studies have reported that citrate increases aluminum absorption by 4.6- to 50-fold in healthy subjects. Patients with renal insufficiency are particularly at risk of developing hyperaluminemia and encephalopathy. Fatalities have been reported. Patients with renal failure or on hemodialysis may also be at risk from soft drinks and effervescent and dispersible drug formulations that contain citrates or citric acid. It is unknown what effect citrus fruits or juices would have on aluminum absorption in healthy patients.

MANAGEMENT: The concomitant use of aluminum- and citrate-containing products and foods should be avoided by renally impaired patients. Hemodialysis patients should especially be cautioned about effervescent and dispersible over-the-counter remedies and soft drinks. Some experts also recommend that healthy patients should separate doses of aluminum-containing antacids and citrates by 2 to 3 hours.

ADJUST DOSING INTERVAL: The administration of aluminum-containing antacids with enteral nutrition may result in precipitation, formation of bezoars, and obstruction of feeding tubes. The proposed mechanism is the formation of an insoluble complex between the aluminum and the protein in the enteral feeding. Several cases of esophageal plugs and nasogastric tube obstructions have been reported in patients receiving high-protein liquids and an aluminum hydroxide-magnesium hydroxide antacid or an aluminum hydroxide antacid.

MANAGEMENT: Some experts recommend that antacids should not be mixed with or given after high protein formulations, that the antacid dose should be separated from the feeding by as much as possible, and that the tube should be thoroughly flushed before administration.

ADJUST DOSING INTERVAL: Administration with food may increase the absorption of calcium. However, foods high in oxalic acid (spinach or rhubarb), or phytic acid (bran and whole grains) may decrease calcium absorption.

MANAGEMENT: Calcium may be administered with food to increase absorption. Consider withholding calcium administration for at least 2 hours before or after consuming foods high in oxalic acid or phytic acid.

ADJUST DOSE: Smoking may decrease the plasma concentrations of riociguat. The proposed mechanism is induction of the CYP450 1A1-mediated metabolism of riociguat by polycyclic aromatic hydrocarbons present in cigarette smoke. CYP450 1A1 is responsible for the formation of the major active metabolite, M1, which has just 1/3 to 1/10 the pharmacologic activity of riociguat. According to the product labeling, plasma concentrations of riociguat are reduced by 50% to 60% in smokers compared to nonsmokers.

MANAGEMENT: Patients should be advised to stop smoking. Riociguat dosages higher than 2.5 mg three times a day may be considered in cigarette smokers, if tolerated, to match the exposure seen in nonsmoking patients. However, safety and effectiveness of higher dosages have not been established. A dosage reduction should be considered in patients who stop smoking during treatment with riociguat. The tablet form of riociguat can generally be taken with or without food. Some authorities recommend not to switch between fed and fasted riociguat intake because of increased peak plasma levels of riociguat in the fasting compared to the fed state.