Magnesium stearate incompatibilities

It is important for the formulator of a new drug substance to know with which excipients he can work and with which he cannot. Some pharmaceutical incompatibilities are known to the formulator, e.g., magnesium stearate/aspirin, and glucose/amines [53],... 

Fig. 20 DSC curves of 10% drug substance with excipients 1) Original curves 2) curves after 1 month at 50°C/<30% RH and 3) 50°C/75% RH. The initial DSC curves suggest an incompatibility only with mannitol and magnesium stearate. The DSC curves (curves 3) after storage at 50°C/75% RH allow the differentiation of the excipients degradation with stearic acid, calcium sulfate dihydrate, and avicel.

Differential scanning calorimetry experiments with some directly compressible tablet excipients suggests that aspartame is incompatible with dibasic calcium phosphate and also with the lubricant magnesium stearate. Reactions between aspartame and sugar alcohols are also known. 

Incompatible with strong acids, alkalis, and iron salts. Avoid mixing with strong oxidizing materials. Magnesium stearate cannot be used in products containing aspirin, some vitamins, and most alkaloidal salts. 

Sodium stearyl fumarate is supplied in a pure form and is often of value when the less pure stearate-type lubricants are unsuitable owing to chemical incompatibility. Sodium stearyl fumarate is less hydrophobic than magnesium stearate or stearic acid and has a less retardant effect on tablet dissolution than magnesium stearate. A specification for sodium stearyl fumarate is contained in the Food Ghemicals Godex (FGC). 

FIGURE 9.10 HSDSC traces for 1 1 mixtures of aspiring with lactose (top) and magnesium stearate (bottom) following a step-isothermal temperature program. Aspirin/lactose shows no apparent incompatibility whereas aspirin/magnesium stearate shows a considerable heat response. (Wissing, 2000, unpublished data.)... 

Polymethacrylates (Eudragit ME SOD and Eudragit RS SOD) can be used as binders in aqueous or nonaqueous wet-granulation processes. They are supplied as S0% aqueous dispersions. Dilution with water prior to use is recommended. Eudragit RS SOD is incompatible with magnesium stearate. 

Finally it should be noted that certain restrictions may have to be incorporated into the packaging material specification, e.g. No lubricants to be used , (magnesium and zinc stearate or similar lubricants may be incompatible with either the drug substance or certain excipients). 

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