What is magnesium hydroxide

Magnesium hydroxide Mg(OH)₂ also called milk of magnesia or magnesia magma, is most commonly used an antacid for heartburn/indigestion or a laxative in either an oral liquid suspension or chewable tablet form. Magnesium hydroxide promotes bowel evacuation by causing osmotic retention of fluid which distends the colon with increased peristaltic activity; reacts with hydrochloric acid in stomach to form magnesium chloride. Magnesium hydroxide is sometimes prescribed for other uses; ask your doctor or pharmacist for more information. Additionally, magnesium hydroxide has smoke supressing and flame retardant properties and is thus used commercially as a fire retardant. Magnesium hydroxide can also be used topically as an antiperspirant underarm deodorant or for relief of canker sores (aphthous ulcers).

Magnesium hydroxide is also used as a residual fuel-oil additive, an alkali drying agent in food, a color-retention agent, an ingredient of toothpaste and frozen desserts, a clarifier in sugar refining, and a neutralizing agent in the chemical industry ¹. Magnesium hydroxide Mg(OH)₂ is categorized by the U.S. Food and Drug Administration (FDA) as a GRAS (generally recognized as safe) food ingredient and is approved for use as a nutritional supplement and a pH-control agent in foods ².

Mg(OH)₂ is used as an flame retardant in commercial furniture applications in the United States and in commercial and residential furniture in the United Kingdom ³. The stability of magnesium hydroxide at temperatures above 300°C allows it to be incorporated into several polymers ⁴. Market-volume data published in 1993 suggest increasing the use of magnesium hydroxide as a flame retardant. About 2,000 and 3,000 tons of magnesium hydroxide were marketed as an Fire Retardant in the United States in 1986 and 1993, respectively ⁴.

Figure 1. Magnesium hydroxide

When administered orally, magnesium hydroxide Mg(OH)₂ dissociates in stomach acids to magnesium (Mg²⁺) cations. About 5–15% of the dissociated magnesium (Mg²⁺) cations are absorbed ⁵ through the epithelial lining of the small intestine (Sutton and Dirks 1986; Elin 1987). Absorption of magnesium (Mg²⁺) can be affected by the presence of food or other substances that readily complex with magnesium (Mg²⁺) cations. Magnesium hydroxide Mg(OH)₂ and magnesium oxide (MgO), which have relatively low solubilities at neutral and alkaline pH, are less completely absorbed than the more water-soluble Mg²⁺compounds-magnesium chloride (MgCl₂), magnesium citrate, and magnesium lactate ⁶. Determination of increased plasma or urinary Mg²⁺ cations after oral administration of Mg(OH)₂ is not possible, because of rapid homeostasis of exogenous Mg²⁺ in humans ⁶.

A single study in human volunteers measured the oral absorption of magnesium (Mg²⁺) cations ⁶. In that study, six healthy males were administered a single oral dose of 360 mg of ²⁶Mg²⁺ as magnesium lactate or citrate and absorption of magnesium (Mg²⁺) over 5 days was found to be 34.5%±18.8% and 39.8%± 24.3% based on urinary excretion. Absorption of magnesium (Mg²⁺) was 25.6% ±34.5%; this estimate was based on fecal excretion.

Magnesium hydroxide in pregnancy

There are no studies in humans that evaluated reproductive or developmental effects associated with the ingestion of magnesium hydroxide.

Magnesium crosses the placenta; serum concentrations in the fetus are similar to those in the mother. The American Gastroenterological Association considers the use of magnesium containing antacids to be low risk in pregnancy.

Other magnesium salts (such as magnesium sulfate) have been used extensively during pregnancy in large doses with no reports of congenital defects. Magnesium hydroxide should only be given in pregnancy when benefit outweighs risk.

Oral administration of MgCl₂ solution caused no toxic signs in pregnant Wistar rats and no increases in the incidences of fetal malformations that were given doses of 0, 200, 400, or 800 mg/kg per day (Mg²⁺ at 0, 24, 47, and 96 mg/kg-d) on day 6 through 15 of pregnancy ⁷. Pregnant dams were killed on day 20 of pregnancy and all fetuses underwent pathological examination for skeletal and visceral malformations. No malformations were observed at any dose tested. The authors concluded that the No-observed-adverse-effect level (NOAEL) for developmental and maternal toxicity was over 800 mg/kg per day (equivalent to 96 mg Mg²⁺/kg per day) in this study ⁷.

Twenty-seven hypertensive women were treated with magnesium hydroxide during the third trimester of pregnancy; no effect was noted on the newborns, except a slight increase in body weight in the children born to the treated mothers vs. controls ⁸. Cord serum levels of magnesium were reported to be 70-100% of the maternal levels after maternal therapy. In such cases, neurological depression may occur in the neonate, characterized by respiratory depression, muscle weakness, and decreased reflexes ⁸. No decrease in Apgar scores was noted in infants of females treated for pregnancy-induced hypertension, although the magnesium levels in the infants reflected hypermagnesiumemia (high blood magnesium levels). Prolonged magnesium treatment during pregnancy may be associated with maternal and fetal hypocalcemia (low blood calcium levels) and adverse effects on fetal bone mineralization ⁸.

Magnesium hydroxide and breastfeeding

A study on the use of magnesium hydroxide during breastfeeding found no adverse reactions in breastfed infants. Intravenous magnesium increases milk magnesium concentrations only slightly. Oral absorption of magnesium by the infant is poor, so maternal magnesium hydroxide is not expected to affect the breastfed infant’s serum magnesium. Magnesium hydroxide supplementation during pregnancy might delay the onset of lactation, but it can be taken during breastfeeding and no special precautions are required.

Ten women with pre-eclampsia were given 4 grams of magnesium sulfate intravenously followed by 1 gram per hour until 24 hours after delivery. While the average serum magnesium was 35.5 mg/L in treated women compared to 18.2 mg/L in 5 untreated controls, colostrum magnesium levels at the time of discontinuation of the infusion was 64 mg/L in treated women and 48 mg/L in the controls. By 48 hours after discontinuation, colostrum magnesium levels were only slightly above control values and by 72 hours they were virtually identical to controls ⁹.

Fifty mothers who were in the first day postpartum received 15 mL of either mineral oil or an emulsion of mineral oil and magnesium hydroxide equivalent to 900 mg of magnesium hydroxide, although the exact number who received each product was not stated. Additional doses were given on subsequent days if needed. None of the breastfed infants were noted to have any markedly abnormal stools, but all of the infants also received supplemental feedings ¹⁰.

One mother who received intravenous magnesium sulfate for 3 days for pregnancy-induced hypertension had lactogenesis II delayed until day 10 postpartum. No other specific cause was found for the delay, although a complete work-up was not done ¹¹. A subsequent controlled clinical trial found no evidence of delayed lactation in mothers who received intravenous magnesium sulfate therapy ¹². Some, but not all, studies have found a trend toward increased time to the first feeding or decreased sucking in infants of mothers treated with intravenous magnesium sulfate during labor because of placental transfer of magnesium to the fetus ¹³.

A study in 40 pairs of matched healthy women with vaginally delivered singleton pregnancies, outcome endpoints were compared in those receiving continuous oral magnesium aspartate HCl supplementation mean dose of 459 mg daily (range 365 to 729 mg of magnesium daily) for at least 4 weeks before delivery versus non-supplemented controls. In the magnesium group, significantly fewer women could breastfeed their infants exclusively at discharge (63% vs 80%) ¹⁴.

Magnesium hydroxide uses

Antacid: For the temporary relief of heartburn, upset stomach, sour stomach, or acid indigestion.

Laxative (occasional constipation): For relief of occasional constipation. This product generally produces bowel movement in 30 minutes to 6 hours.

Magnesium hydroxide come as a tablet and liquid to take by mouth. It usually is taken as needed for constipation. Follow the directions on the package or on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand. Take magnesium hydroxide exactly as directed. Do not take more or less of it or take it more often than prescribed by your doctor.

Shake the liquid well before each use. All doses should be followed by 8 ounces of water.

Before taking magnesium hydroxide:

• tell your doctor and pharmacist if you are allergic to magnesium hydroxide or any other drugs.
• tell your doctor and pharmacist what prescription and nonprescription medications you are taking, including vitamins.
• tell your doctor if you have or have ever had kidney disease.
• tell your doctor if you are pregnant, plan to become pregnant, or are breast-feeding. If you become pregnant while taking magnesium hydroxide, call your doctor.

Drug Interactions

Acalabrutinib: Antacids may decrease the serum concentration of Acalabrutinib. Management: Separate administration of acalabrutinib from the administration of any antacids by at least 2 hours in order to minimize the potential for a significant interaction. Consider therapy modification

Alfacalcidol: May increase the serum concentration of Magnesium Salts. Consider therapy modification

Allopurinol: Antacids may decrease the absorption of Allopurinol. Consider therapy modification

Alpha-Lipoic Acid: Magnesium Salts may decrease the absorption of Alpha-Lipoic Acid. Alpha-Lipoic Acid may decrease the absorption of Magnesium Salts. Consider therapy modification

Amphetamines: Antacids may decrease the excretion of Amphetamines. Monitor therapy

Antipsychotic Agents (Phenothiazines): Antacids may decrease the absorption of Antipsychotic Agents (Phenothiazines). Monitor therapy

Atazanavir: Antacids may decrease the absorption of Atazanavir. Consider therapy modification

Bictegravir: Antacids may decrease the serum concentration of Bictegravir. Management: Bictegravir, emtricitabine, and tenofovir alafenamide can be administered while fasting at least 2 hours before antacids. Giving with or 2 hours after antacids is not recommended. Consider therapy modification

Bisacodyl: Antacids may diminish the therapeutic effect of Bisacodyl. Antacids may cause the delayed-release bisacodyl tablets to release drug prior to reaching the large intestine. Gastric irritation and/or cramps may occur. Consider therapy modification

Bismuth Subcitrate: Antacids may diminish the therapeutic effect of Bismuth Subcitrate. Management: Avoid administration of antacids within 30 minutes of bismuth subcitrate (tripotassium bismuth dicitrate) administration. Consider therapy modification

Bisphosphonate Derivatives: Antacids may decrease the serum concentration of Bisphosphonate Derivatives. Management: Avoid administration of antacids containing polyvalent cations within: 2 hours before or after tiludronate/clodronate/etidronate; 60 minutes after oral ibandronate; or 30 minutes after alendronate/risedronate. Exceptions: Pamidronate; Zoledronic Acid. Consider therapy modification

Bisphosphonate Derivatives: Magnesium Salts may decrease the serum concentration of Bisphosphonate Derivatives. Management: Avoid administration of oral magnesium salts within: 2 hours before or after tiludronate/clodronate/etidronate; 60 minutes after oral ibandronate; or 30 minutes after alendronate/risedronate. Exceptions: Pamidronate; Zoledronic Acid. Consider therapy modification

Bosutinib: Antacids may decrease the serum concentration of Bosutinib. Management: Administer antacids more than 2 hours before or after bosutinib. Consider therapy modification

Bromperidol: Antacids may decrease the absorption of Bromperidol. Monitor therapy

Calcitriol (Systemic): May increase the serum concentration of Magnesium Salts. Management: Consider using a non-magnesium-containing antacid or phosphate-binding product in patients also receiving calcitriol. If magnesium-containing products must be used with calcitriol, serum magnesium concentrations should be monitored closely. Consider therapy modification

Calcium Channel Blockers: May enhance the adverse/toxic effect of Magnesium Salts. Magnesium Salts may enhance the hypotensive effect of Calcium Channel Blockers. Monitor therapy

Calcium Polystyrene Sulfonate: Laxatives (Magnesium Containing) may enhance the adverse/toxic effect of Calcium Polystyrene Sulfonate. More specifically, concomitant use of calcium polystyrene sulfonate with magnesium-containing laxatives may result in metabolic alkalosis or with sorbitol may result in intestinal necrosis. Management: Avoid concomitant use of calcium polystyrene sulfonate (rectal or oral) and magnesium-containing laxatives. Avoid combination

Captopril: Antacids may decrease the serum concentration of Captopril. Monitor therapy

Cefditoren: Antacids may decrease the serum concentration of Cefditoren. Management: Concomitant use of cefditoren with antacids is not recommended. Consider alternative methods to control acid reflux (eg, diet modification) or alternative antimicrobial therapy. If antacid therapy can not be avoided, separate dosing by several hours. Consider therapy modification

Cefpodoxime: Antacids may decrease the serum concentration of Cefpodoxime. Monitor therapy

Cefuroxime: Antacids may decrease the serum concentration of Cefuroxime. Management: Administer cefuroxime axetil at least 1 hour before or 2 hours after the administration of short-acting antacids. Consider therapy modification

Chloroquine: Antacids may decrease the serum concentration of Chloroquine. Management: Separate administration of antacids and chloroquine by at least 4 hours to minimize any potential negative impact of antacids on chloroquine bioavailability. Consider therapy modification

Corticosteroids (Oral): Antacids may decrease the bioavailability of Corticosteroids (Oral). Management: Consider separating doses by 2 or more hours. Budesonide enteric coated tablets could dissolve prematurely if given with drugs that lower gastric acid, with unknown impact on budesonide therapeutic effects. Consider therapy modification

Cysteamine (Systemic): Antacids may diminish the therapeutic effect of Cysteamine (Systemic). Monitor therapy

Dabigatran Etexilate: Antacids may decrease the serum concentration of Dabigatran Etexilate. Management: Dabigatran etexilate Canadian product labeling recommends avoiding concomitant use with antacids for 24 hours after surgery. In other situations, administer dabigatran etexilate 2 hours prior to antacids. Monitor clinical response to dabigatran therapy. Consider therapy modification

Dasatinib: Antacids may decrease the absorption of Dasatinib. Consider therapy modification

Deferiprone: Antacids may decrease the serum concentration of Deferiprone. Management: Separate administration of deferiprone and oral medications or supplements that contain polyvalent cations by at least 4 hours. Consider therapy modification

Deferiprone: Magnesium Salts may decrease the serum concentration of Deferiprone. Management: Separate administration of deferiprone and oral medications or supplements that contain polyvalent cations by at least 4 hours. Consider therapy modification

Delavirdine: Antacids may decrease the serum concentration of Delavirdine. Management: Separate doses of delavirdine and antacids by at least 1 hour. Monitor for decreased delavirdine therapeutic effects with this combination. Consider therapy modification

Dexmethylphenidate: Antacids may increase the absorption of Dexmethylphenidate. Specifically, antacids may interfere with the normal release of drug from the extended-release capsules (Focalin XR brand), which could result in both increased absorption (early) and decreased delayed absorption. Monitor therapy

Diacerein: Antacids may decrease the absorption of Diacerein. Monitor therapy

Dolutegravir: Magnesium Salts may decrease the serum concentration of Dolutegravir. Management: Administer dolutegravir at least 2 hours before or 6 hours after oral magnesium salts. Administer the dolutegravir/rilpivirine combination product at least 4 hours before or 6 hours after oral magnesium salts. Consider therapy modification

Doxercalciferol: May enhance the hypermagnesemic effect of Magnesium Salts. Management: Consider using a non-magnesium-containing antacid or phosphate-binding product in patients also receiving doxercalciferol. If magnesium-containing products must be used with doxercalciferol, serum magnesium concentrations should be monitored closely. Consider therapy modification

Eltrombopag: Magnesium Salts may decrease the serum concentration of Eltrombopag. Management: Administer eltrombopag at least 2 hours before or 4 hours after oral administration of any magnesium-containing product. Consider therapy modification

Elvitegravir: Antacids may decrease the serum concentration of Elvitegravir. Management: Separate administration of antacids and elvitegravir-containing products by at least 2 hours in order to minimize the risk for an interaction. Consider therapy modification

Erlotinib: Antacids may decrease the serum concentration of Erlotinib. Management: Separate the administration of erlotinib and any antacid by several hours in order to minimize the risk of a significant interaction. Consider therapy modification

Fexofenadine: Antacids may decrease the serum concentration of Fexofenadine. Management: No specific recommendations concerning the time required between their administration are provided. Separate administration of each agent by as much time as possible to decrease the risk of an interaction. Consider therapy modification

Fosinopril: Antacids may decrease the serum concentration of Fosinopril. Management: The US and Canadian fosinopril manufacturer labels recommend separating the doses of antacids and fosinopril by 2 hours. Consider therapy modification

Gabapentin: Antacids may decrease the serum concentration of Gabapentin. Management: Administer gabapentin at least 2 hours after antacid administration. Monitor patients closely for evidence of reduced response to gabapentin therapy when both of these drugs are being used. Consider therapy modification

Gabapentin: Magnesium Salts may enhance the CNS depressant effect of Gabapentin. Specifically, high dose intravenous/epidural magnesium sulfate may enhance the CNS depressant effects of gabapentin. Magnesium Salts may decrease the serum concentration of Gabapentin. Management: Administer gabapentin at least 2 hours after oral magnesium salts administration. Monitor patients closely for evidence of reduced response to gabapentin therapy. Monitor for CNS depression if high dose IV/epidural magnesium sulfate is used. Consider therapy modification

Gefitinib: Antacids may decrease the serum concentration of Gefitinib. Management: Administer gefitinib at least 6 hours before or after administration of an antacid, and closely monitor clinical response to gefitinib. Consider therapy modification

Hyoscyamine: Antacids may decrease the serum concentration of Hyoscyamine. Management: Administer immediate release hyoscyamine before meals and antacids after meals when these agents are given in combination. Consider therapy modification

Iron Salts: Antacids may decrease the absorption of Iron Salts. Exceptions: Ferric Carboxymaltose; Ferric Citrate; Ferric Gluconate; Ferric Hydroxide Polymaltose Complex; Ferric Pyrophosphate Citrate; Ferumoxytol; Iron Dextran Complex; Iron Isomaltoside; Iron Sucrose. Consider therapy modification

Itraconazole: Antacids may decrease the serum concentration of Itraconazole. Management: Administer itraconazole at least 1 hour after and 2 hours before administration of any antacids. Itraconazole oral suspension may be less sensitive to the effects of decreased gastric acidity. Consider therapy modification

Ketoconazole (Systemic): Antacids may decrease the serum concentration of Ketoconazole (Systemic). Management: Administer oral ketoconazole at least 2 hours prior to use of any antacid product. Monitor patients closely for signs of inadequate clinical response to ketoconazole. Consider therapy modification

Lanthanum: Antacids may diminish the therapeutic effect of Lanthanum. Consider therapy modification

Ledipasvir: Antacids may decrease the serum concentration of Ledipasvir. Management: Separate the administration of ledipasvir and antacids by 4 hours. Consider therapy modification

Levothyroxine: Magnesium Salts may decrease the serum concentration of Levothyroxine. Management: Separate administration of oral levothyroxine and oral magnesium salts by at least 4 hours. Consider therapy modification

Mesalamine: Antacids may diminish the therapeutic effect of Mesalamine. Antacid-mediated increases in gastrointestinal pH may cause the premature release of mesalamine from specific sustained-release mesalamine products. Management: Avoid concurrent administration of antacids with sustained-release mesalamine products. Separating antacid and mesalamine administration, and/or using lower antacid doses may be adequate means of avoiding this interaction. Consider therapy modification

Methenamine: Antacids may diminish the therapeutic effect of Methenamine. Consider therapy modification

Methylphenidate: Antacids may increase the absorption of Methylphenidate. Specifically, antacids may interfere with the normal release of drug from the extended-release capsules (Ritalin LA brand), which could result in both increased absorption (early) and decreased delayed absorption. Monitor therapy

MiSOPROStol: Antacids may enhance the adverse/toxic effect of MiSOPROStol. More specifically, concomitant use with magnesium-containing antacids may increase the risk of diarrhea. Management: Avoid concomitant use of misoprostol and magnesium-containing antacids. In patients requiring antacid therapy, employ magnesium-free preparations. Monitor for increased adverse effects (e.g., diarrhea, dehydration). Avoid combination

Multivitamins/Fluoride (with ADE): Magnesium Salts may decrease the serum concentration of Multivitamins/Fluoride (with ADE). Specifically, magnesium salts may decrease fluoride absorption. Management: To avoid this potential interaction separate the administration of magnesium salts from administration of a fluoride-containing product by at least 1 hour. Consider therapy modification

Multivitamins/Minerals (with ADEK, Folate, Iron): Antacids may decrease the serum concentration of Multivitamins/Minerals (with ADEK, Folate, Iron). Specifically, antacids may decrease the absorption of orally administered iron. Management: Separate dosing of oral iron-containing multivitamin preparations and antacids by as much time as possible in order to minimize impact on therapeutic efficacy of the iron preparation. Consider therapy modification

Mycophenolate: Antacids may decrease the absorption of Mycophenolate. Management: Separate doses of mycophenolate and antacids by at least 2 hours. Monitor for reduced effects of mycophenolate if taken concomitant with antacids. Consider therapy modification

Mycophenolate: Magnesium Salts may decrease the serum concentration of Mycophenolate. Management: Separate doses of mycophenolate and oral magnesium salts. Monitor for reduced effects of mycophenolate if taken concomitant with oral magnesium salts. Consider therapy modification

Neratinib: Antacids may decrease the serum concentration of Neratinib. Specifically, antacids may reduce neratinib absorption. Management: Separate the administration of neratinib and antacids by giving neratinib at least 3 hours after the antacid. Consider therapy modification

Neuromuscular-Blocking Agents: Magnesium Salts may enhance the neuromuscular-blocking effect of Neuromuscular-Blocking Agents. Monitor therapy

Nilotinib: Antacids may decrease the serum concentration of Nilotinib. Management: Separate the administration of nilotinib and any antacid by at least 2 hours whenever possible in order to minimize the risk of a significant interaction. Consider therapy modification

PAZOPanib: Antacids may decrease the serum concentration of PAZOPanib. Management: Avoid the use of antacids in combination with pazopanib whenever possible. Separate doses by several hours if antacid treatment is considered necessary. The impact of dose separation has not been investigated. Consider therapy modification

PenicillAMINE: Antacids may decrease the serum concentration of PenicillAMINE. Management: Separate the administration of penicillamine and antacids by at least 1 hour. Consider therapy modification

PenicillAMINE: Magnesium Salts may increase the serum concentration of PenicillAMINE. Management: Separate the administration of penicillamine and oral magnesium salts by at least 1 hour. Consider therapy modification

Phosphate Supplements: Antacids may decrease the absorption of Phosphate Supplements. Management: This applies only to oral phosphate administration. Separating administer of oral phosphate supplements from antacid administration by as long as possible may minimize the interaction. Exceptions: Sodium Glycerophosphate Pentahydrate. Consider therapy modification

Phosphate Supplements: Magnesium Salts may decrease the serum concentration of Phosphate Supplements. Management: Administer oral phosphate supplements as far apart from the administration of an oral magnesium salt as possible to minimize the significance of this interaction. Exceptions: Sodium Glycerophosphate Pentahydrate. Consider therapy modification

Potassium Phosphate: Antacids may decrease the serum concentration of Potassium Phosphate. Management: Consider separating administration of antacids and oral potassium phosphate by at least 2 hours to decrease risk of a significant interaction. Consider therapy modification

QuiNIDine: Antacids may decrease the excretion of QuiNIDine. Monitor therapy

QuiNINE: Antacids may decrease the serum concentration of QuiNINE. Avoid combination

Quinolones: Antacids may decrease the absorption of Quinolones. Of concern only with oral administration of quinolones. Management: Avoid concurrent administration of quinolones and antacids to minimize the impact of this interaction. Recommendations for optimal dose separation vary by specific quinolone. Exceptions: LevoFLOXacin (Oral Inhalation). Consider therapy modification

Quinolones: Magnesium Salts may decrease the serum concentration of Quinolones. Management: Administer oral quinolones several hours before (4 h for moxi/pe/spar-, 2 h for others) or after (8 h for moxi-, 6 h for cipro/dela-, 4 h for lome/pe-, 3 h for gemi-, and 2 h for levo-, nor-, or ofloxacin or nalidixic acid) oral magnesium salts. Exceptions: LevoFLOXacin (Oral Inhalation). Consider therapy modification

Raltegravir: Magnesium Salts may decrease the serum concentration of Raltegravir. Management: Avoid the use of oral / enteral magnesium salts with raltegravir. No dose separation schedule has been established that adequately reduces the magnitude of interaction. Avoid combination

Rilpivirine: Antacids may decrease the serum concentration of Rilpivirine. Management: Administer antacids at least 2 hours before or 4 hours after rilpivirine. Administer antacids at least 6 hours before or 4 hours after the rilpivirine/dolutegravir combination product. Consider therapy modification

Riociguat: Antacids may decrease the serum concentration of Riociguat. Management: Separate the administration of antacids and riociguat by at least 1 hour in order to minimize any potential interaction. Consider therapy modification

Rosuvastatin: Antacids may decrease the serum concentration of Rosuvastatin. Monitor therapy

Sodium Polystyrene Sulfonate: Laxatives (Magnesium Containing) may enhance the adverse/toxic effect of Sodium Polystyrene Sulfonate. More specifically, concomitant use of sodium polystyrene sulfonate with magnesium-containing laxatives may result in metabolic alkalosis or with sorbitol may result in intestinal necrosis. Management: Avoid concomitant use of sodium polystyrene sulfonate (rectal or oral) and magnesium-containing laxatives. Avoid combination

Sotalol: Antacids may decrease the serum concentration of Sotalol. Management: Avoid simultaneous administration of sotalol and antacids. Administer antacids 2 hours after sotalol. Consider therapy modification

Strontium Ranelate: Magnesium Hydroxide may decrease the serum concentration of Strontium Ranelate. Management: Separate administration of strontium ranelate and magnesium hydroxide by at least 2 hours whenever possible in order to minimize this interaction. Consider therapy modification

Sulpiride: Antacids may decrease the serum concentration of Sulpiride. Management: Separate administration of antacids and sulpiride by at least 2 hours in order to minimize the impact of antacids on sulpiride absorption. Consider therapy modification

Tetracyclines: Antacids may decrease the absorption of Tetracyclines. Management: Separate administration of antacids and oral tetracycline derivatives by several hours when possible to minimize the extent of this potential interaction. Consider therapy modification

Tetracyclines: Magnesium Salts may decrease the absorption of Tetracyclines. Only applicable to oral preparations of each agent. Consider therapy modification

Trientine: Antacids may decrease the absorption of Trientine. Management: Separate trientine dosing from other oral drugs (eg, antacids) by at least 1 hour. Monitor for decreased therapeutic effects of trientine if an antacid is initiated/dose increased, or increased effects if an antacid is discontinued/dose decreased. Consider therapy modification

Trientine: May decrease the serum concentration of Magnesium Salts. Magnesium Salts may decrease the serum concentration of Trientine. Consider therapy modification

Velpatasvir: Antacids may decrease the serum concentration of Velpatasvir. Management: Separate administration of velpatasvir and antacids by at least 4 hours. Consider therapy modification

Warnings and Precautions

Disease-related concerns:

• Neuromuscular disease: Use with extreme caution in patients with myasthenia gravis or other neuromuscular disease.
• Renal impairment: Use with caution in patients with renal impairment; accumulation of magnesium may lead to magnesium intoxication.

Other warnings and precautions

• For occasional use only; serious side effects may occur with prolonged use. For use only under the supervision of a health care provider in patients with kidney dysfunction, a magnesium-restricted diet, stomach pain/nausea/vomiting, or with a sudden change in bowel habits which persist for >2 weeks. Patients should stop use as a laxative and notify health care provider of any rectal bleeding, if bowel movement does not occur after using product, or if use is needed for >1 week. Stop use as an antacid and notify health care provider if you have taken the maximum dose for >2 weeks. Not for over-the-counter use in children <2 years of age.

Magnesium hydroxide dosage

Adult Antacid (OTC Oral) Dose

• Liquid: Magnesium hydroxide 400 mg/5 mL: 5 to 15 mL as needed up to 4 times/day; do not exceed 60 mL in 24 hours
• Tablet, chewable: Magnesium hydroxide 311 mg/tablet: 2 to 4 tablets every 4 hours up to 4 times/day; do not exceed 4 doses in 24 hours

Adult Laxative (occasional constipation) Oral Dose

Liquid:

• Magnesium hydroxide 400 mg/5 mL: 30 to 60 mL/day once daily at bedtime or in divided doses
• Magnesium hydroxide 800 mg/5 mL: 15 to 30 mL/day once daily at bedtime or in divided doses
• Magnesium hydroxide 1,200 mg/5 mL: 10 to 20 mL/day once daily at bedtime or in divided doses

Tablet, chewable:

• Magnesium hydroxide 311 mg/tablet: 8 tablets/day once daily at bedtime or in divided doses

Pediatric Antacid (OTC Oral) Dose

• Liquid: Magnesium hydroxide 400 mg/5 mL: Children ≥12 years: Refer to adult dosing.
• Tablet, chewable: Magnesium hydroxide 311 mg/tablet:

Children <12 years: Use NOT recommended.

Children ≥12 years: Refer to adult dosing.

Pediatric Laxative (occasional constipation) Oral Dose

Liquid:

• Children <2 years: Use NOT recommended.
• Children 2 to 5 years: Magnesium hydroxide 400 mg/5 mL: 5 to 15 mL/day once daily at bedtime or in divided doses
• Children 6 to 11 years:
  • Magnesium hydroxide 400 mg/5 mL: 15 to 30 mL/day once daily at bedtime or in divided doses
  • Magnesium hydroxide 1,200 mg/5 mL: 5 to 10 mL/day once daily at bedtime or in divided doses
• Children ≥12 years: Refer to adult dosing.

Tablet, chewable Magnesium hydroxide 311 mg/tablet:

• Children <3 years: Use NOT recommended.
• Children 3 to 5 years: 2 tablets/day once daily at bedtime or in divided doses
• Children 6 to 11 years: 4 tablets/day once daily at bedtime or in divided doses
• Children ≥12 years: Refer to adult dosing.

Tablet, chewable Magnesium hydroxide 400 mg/tablet:

• Children <2 years: Use NOT recommended.
• Children 2 to 5 years: 1 to 3 tablets/day once daily or in divided doses (maximum daily dose: 3 tablets)
• Children 6 to 11 years: 3 to 6 tablets/day once daily or in divided doses (maximum daily dose: 6 tablets)

What should I do if I forget a dose?

This medication usually is taken as needed. If your doctor has told you to take magnesium hydroxide regularly, take the missed dose as soon as you remember it. However, if it is almost time for the next dose, skip the missed dose and continue your regular dosing schedule. Do not take a double dose to make up for a missed one.

Magnesium hydroxide side effects

Magnesium hydroxide may cause side effects. If you experience any of the following symptoms, call your doctor immediately:

• stomach cramps
• upset stomach
• vomiting
• diarrhea

If you experience a serious side effect, you or your doctor may send a report to the Food and Drug Administration’s (FDA) MedWatch Adverse Event Reporting program online (https://www.fda.gov/Safety/MedWatch/default.htm).

Gastrointestinal side effects

Diarrhea may occur and is occasionally severe enough to cause dehydration and electrolyte abnormalities.

Gastrointestinal side effects have included diarrhea and minor gastrointestinal discomfort.

General side effects

General side effects have included signs and symptoms of hypermagnesemia. These have included hypotension, nausea, vomiting, EKG changes, respiratory depression, mental depression and coma.

Magnesium may be systemically absorbed following administration of magnesium hydroxide. In patients with normal renal function, increased magnesium elimination in the urine occurs and no significant changes in serum magnesium levels would be expected. However, magnesium may accumulate in patients with renal insufficiency.

Tell your doctor or get medical help right away if you have any of the following signs or symptoms that may be related to a very bad side effect:

• Signs of an allergic reaction, like rash; hives; itching; red, swollen, blistered, or peeling skin with or without fever; wheezing; tightness in the chest or throat; trouble breathing, swallowing, or talking; unusual hoarseness; or swelling of the mouth, face, lips, tongue, or throat.
• Very upset stomach or throwing up.
• Very loose stools (diarrhea).
• Not hungry.
• Muscle weakness.

A 28 yr old ingested magnesium hydroxide-aluminum hydroxide simethicone (average daily consumption of 21 g each of magnesium hydroxide and aluminum hydroxide) and developed phosphate depletion, nephrolithiasis, and bilateral ureteric obstruction ¹⁵. Myalgia, weakness, and bone pain were absent. Biochemical features included hypophosphatemia, hypercalcemia, hypophosphatasia, elevated plasma 1,2-dihydroxyvitamin D level, and low plasma intact parathyroid hormone level. These abnormalities were corrected when antacid ingestion was reduced and phosphate intake supplemented.

Magnesium hydroxide laxatives administered to infants and neonates may induce symptoms of severe magnesium intoxication with elevated serum magnesium levels. Renal immaturity may be a factor ¹⁶.

Most available toxicity data on magnesium hydroxide describe effects of acute exposure to magnesium hydroxide or of prolonged exposure to antacid or laxative products containing Mg(OH)₂. Magnesium intoxication has been reported in infants (2–42 days old) that received Mg²⁺-containing oral laxatives at Mg²⁺ doses of 224–917 mg/kg per day for 2–11 days ¹⁷. Whereas normal serum magnesium ranges from 1.4 to 2.4 mEq/L, these infants had concentrations of 3.5–11.7 mEq/L. In one case, Mg²⁺ body burden was high enough to cause perforation of the bowel ¹⁷.

In adults, serious toxic effects associated with excess magnesium intake occur at very high intake levels equating to serum concentrations of 4 mEq/L ¹⁸. Toxicity has been limited to persons with intestinal or renal disease ¹⁹. The Hazardous Substance Data Bank entry for magnesium hydroxide states that the probable oral lethal dose of magnesium hydroxide in humans is 5–15 g/kg in a 70-kg person ²⁰. Cardiac arrest has been reported at serum Mg²⁺ concentrations of 15–16 mEq/L ²¹. Respiratory depression, depression of the central nervous system, and coma occur in adult patients with plasma Mg²⁺ concentrations of 10–14 mEq/L ²². Hypotension, nausea, and vomiting occur at plasma concentrations of 3–8 mEq/L.

Reported fatal magnesium hydroxide dose

• Probable oral lethal dose is 5 to 15 gram/kg body weight, between 1 pint (473 ml) and 1 quart (946 ml) for a 70 kg (150 lb) person ²⁰.

Cancer

The National Academy of Sciences subcommittee found no oral chronic toxicity studies or epidemiological studies that investigated the carcinogenicity of magnesium hydroxide in rodents or humans. The subcommittee concludes that magnesium hydroxide Mg(OH)₂ is not likely to be carcinogenic to humans by the oral route. No adequate data are available to assess the carcinogenicity of Mg(OH)₂ by the dermal or inhalation or routes of exposure.

Mice fed 0.5% or 2% of aqueous MgCl2 in their diet for 96 weeks (68, or 336 mg/kg per day for males; 87 or 470 mg/kg per day for females) showed no significant change in the incidence of malignant lymphoma and leukemia ²³. Dose-related increases in incidence of malignant lymphoma and leukemia occurred in male mice (controls, five of 50; low dose, seven of 50; high dose, eleven of 50), but not in females (controls, nine of 49; low dose, 17 of 50; high dose, 11 of 50). The incidence of hepatocellular carcinomas in male mice was decreased in a dose-related manner (controls, 13 of 50; low dose, six of 50; high dose, four of 50) and the incidence in high-dose males was significantly different from that in controls. Toxicity in female mice (i.e., decreased body weight) suggests that the study was conducted at or near the maximum tolerated dose for females.

There are insufficient data to assess the carcinogenicity of Mg(OH)₂. EPA, the National Toxicology Program (NTP), and the International Agency for Research on Cancer (IARC) have not evaluated the carcinogenicity of Mg(OH)₂.

A chronic study in mice exposed to Mg(OH)₂ filaments did not find evidence of carcinogenicity. Studies in rats suggest that Mg(OH)₂ incorporated into the diet can protect against some chemically induced cancers ²⁴. The subcommittee is not aware of any mutagenicity data on magnesium hydroxide. However, genotoxicity studies conducted with several magnesium salts have all been negative.

On the basis of the data available, the National Academy of Sciences subcommittee concludes that there are insufficient data on oral carcinogenicity of magnesium hydroxide to determine its carcinogenicity.

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