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Magnesium Stearate Excipient | Uses, Suppliers, and Specifications
Magnesium Stearate is Magnesium Octadecanoate, a synthetic soap that consists of a mixture of magnesium salts of fatty acids, principally palmitic and stearic acid. It is one of the most commonly used excipients and corresponds to the chemical formula, C36H70MgO4. Magnesium stearate is described in pharmacopoeia as a mixture of organic acids, chiefly magnesium stearate, and magnesium palmitate. It is supplied as a very fine, light, white impalpable powder. When touched, it feels greasy and readily adheres to the skin.
Pharmacopoeial Compliance: USP-NF; Ph.Eur; J.P; B.P; I.P
Synonyms and Trade Names: Magnesium Stearate; Dibasic Magnesium Stearate; Magnesium Distrearate; Magnesium Octadecanoate; Octadecanoic Acid, Magnesium Salt; Stearic Acid, Magnesium Salt; Synpro® 90
Uses and Applications: Tablet and Capsule Lubricant and Hydrophobic Agent in Tablet Film Coatings
Description
Magnesium stearate, sometimes known as Magnesium distearate or Dibasic Magnesium stearate, is a synthetic soap consisting of a mixture of magnesium salts of fatty acids, mainly palmitate and stearate in varying proportions. It corresponds to the chemical formula Mg(C18H35O2)2. In the USP-NF, Magnesium stearate is described as a compound of magnesium with a mixture of solid organic acids consisting mainly of varying amounts of magnesium stearate and magnesium palmitate. The PhEur describes Magnesium stearate as a mixture of solid organic acids consisting chiefly of variable levels of Magnesium stearate and Magnesium palmitate.
Magnesium stearate is prepared in any number of ways: the so-called direct methods involve reacting aqueous solutions of magnesium chloride with fatty acids or sodium stearate, and indirect methods which involve a sodium soap is first produced by reacting fatty acids with sodium hydroxide followed by the addition of magnesium oxide, hydroxide, or carbonate to precipitate out the Magnesium stearate.
Magnesium stearate is a very fine, light white, precipitated or milled, impalpable powder of low bulk density, having a faint odour of stearic acid and a characteristic taste. The powder is greasy to the touch and readily adheres to the skin.
Chemical Structure & Identifiers
| Chemical Name | Octadecanoic acid magnesium salt |
| CAS Registry Number | [557-04-0] |
| Empirical Formula | C38H70MgO4 |
| Molecular Weight | 591.24 g/mol |
| EC/ECS Number | 557-04-0 |
| UNII Code (FDA) | 70097M6I30 |
Regulatory Status
Magnesium stearate is an approved excipient. It is listed in all the major pharmacopoeia. It is also GRAS listed and accepted as a food additive in the USA and EU. Magnesium stearate is additionally listed in the US FDA Inactive Ingredients Database (covering oral tablets, tablets and powders, topical preparations; and intravitreal implants and injections). A specification for Magnesium stearate is included in the Food Chemicals Codex (FCC).
Physicochemical Properties
| Physical form | Solid, powder |
| Appearance | Fine, fluffy white powder |
| Bulk density | 0.599 g/ml |
| Tapped density | 0.2 86 g/ml |
| True density | 1.092 g/ml3 |
| Flash point | 250 oC |
| Flowability | Poorly flowing, cohesive powder |
| Melting range | 117 – 1.50 oC |
| Solubility | Practically insoluble in water, ethanol, and ether. Slightly soluble in warm ethanol (95%) |
| Specific surface area (BET) | l.6-14.8 m2/g |
Pharmacopeoeal Specifications
| Test | USP-NF | PhEur | JP |
| Official name | Magnesium stearate | Magnesium stearate | Magnesium stearate |
| Authorised use | Excipient | Excipient | Excipient |
| Definition | specified | specified | specified |
| Identification | specified | specified | specified |
| Characters | n/a | specified | n/a |
| Microbial limits
Aerobic microbes Fungi and yeasts |
≤1000 cfu/g ≤500 cfu/g |
≤103 cfu/g ≤102 cfu/g |
≤1000 cfu/g ≤500 cfu/g |
| Acidity or alkalinity | specified | specified | specified |
| Acid value of the fatty acid | n/a | 195 – 210 | n/a |
| Freezing point | n/a | ³53 | n/a |
| Nickel | n/a | ≤5 ppm | n/a |
| Cadmium | n/a | ≤3 ppm | n/a |
| Specific surface area | + | n/a | n/a |
| Loss on drying | ≤6.0% | ≤6.0% | ≤6.0% |
| Chloride | ≤0.1% | ≤0.1% | ≤0.1% |
| Sulfate | ≤1.0% | ≤1.0% | ≤1.0% |
| Lead | ≤0.001% | ≤10 ppm | n/a |
| Heavy metals | n/a | n/a | ≤20 ppm |
| Relative stearic/palmitic content | + | + | + |
| Assay (dried basis as Mg) | 4.0 – 5.0% | 4.0 – 5.0% | 4.0 – 5.0% |
| Labelling | specified | n/a | n/a |
Key: n/a Specification is not listed
*All claims with respect to conformity are subject to our Terms and Conditions. No express or implied warranty is made for specific properties or fitness for any particular application or purpose.
Applications in Pharmaceutical Formulations or Technology
Magnesium stearate is a popular material that is used in pharmaceutical products, cosmetic formulations, and food products taking advantage of its water barring properties. In oral pharmaceutical products, Magnesium stearate primarily functions as a lubricant in capsule filling machines and tablet machines. In tablet film coatings, Magnesium stearate is used to reduce tack and improve the moisture resistance of coatings. It has also been used in topical medical devices to enhance the performance of barrier creams.
Uses as a Lubricant
Magnesium stearate is one of the most commonly used metallic salt boundary lubricants and excipients. It is relatively inexpensive, chemically stable, and has a high melting point and lubrication property. The typical concentrations vary between 0.25% –1.0% w/w. Higher levels are not recommended due to their deleterious effects on dissolution rate and/or compactibility.
The lubricant effect of magnesium stearate relates to the adherence of the polar moiety on granules/powders, while the lipophilic moiety is oriented outward from the particle’s surface. However, Magnesium stearate has the capacity to form a hydrophobic layer around particles which can lead to reduced water penetration, which compromises the dissolution profile of the drug substance.
Also, when used in plastic deforming fillers and diluents, such as Starch (e.g Maize starch) and Microcrystalline cellulose, Magnesium stearate can lead to tablets of weak strength and high friability. Finally, the amount and the mixing time of Magnesium stearate in the formulation are critical variables. A higher level and longer mixing time reduce the drug dissolution.
Note that commercially available Magnesium stearates are generally a mixture of crystalline forms (anhydrate, monohydrate, dihydrate, and trihydrate). Depending upon the source, Magnesium stearate can differ in morphology, crystallinity, batch-to-batch variability in particle size, surface area, bulk strength, and fatty acid composition. These differences can result in different compression profiles and lubrication efficiency and potentially, differences in hardness and tablet friability.
Other Uses
Magnesium stearate is also used in cosmetic products and topical medical devices to enhance moisture repellant properties. Typical concentrations are between 0.25 and 5% by weight.
Safety and Precautions
Magnesium stearate has been used as a pharmaceutical excipient and is generally regarded as nontoxic following oral administration. However, oral intake of large quantities may produce a laxative effect or mucosal irritation. There is currently no comprehensive toxicity information as far as it relates to normal routes of occupational exposure. Previous toxicity assessments in rat animal models have shown that Magnesium stearate is non-irritant on the skin, and is nontoxic following oral intake or inhalation.
Toxicology: LD50 (rat, inhalation): >2 mg/L; LD50 (rat, oral): > 10g/kg. Not shown to be carcinogenic.
Stability and Storage Conditions
Magnesium stearate is stable and should be stored in a well-dosed container in a cool, dry place. The shelf life is 24-36 months. When handling Magnesium stearate in a work setting, you should observe normal precautions appropriate to the circumstances and quantity of material handled. Eye protection and gloves should be worn. Avoid excessive inhalation of Magnesium stearate dust as it may cause upper respiratory tract discomfort, coughing, and choking. The material should be processed in a well-ventilated environment. In the USA, the OSHA limit is 10 mg/m3 TWA for Magnesium stearate.
Sustainability and Environmental Impact
A sustainability score has not been assigned for Magnesium stearate.
Manufacturers & Suppliers
Mallinckrodt Pharmaceuticals
- Magnesium Stearate NF (1726)
- Magnesium Stearate HyQual™
- Magnesium Stearate Nutraceutical
- Magnesium Stearate Food Grade
- LIGAMED® MF-2-V
- LIGAMED® MF-2-V-BI
- LIGAMED® MF-3-V
- LIGAMED® MF-2-V-BI
- LIGAMED® MF-2-K
- LIGAMED® MF-3-K
Additional Resources (Downloads)
References and Literature Used
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