Magnesium stearate concentration

Fig. 12 Tensile strength of calcium sulfate tablets as a function of magnesium stearate concentration (solid fraction = 0.57). (From Ref. 29.)...

Interestingly, exceptions are possible. Stewart et al. [81] reported that the effect of magnesium stearate concentration on the dissolution of a model low-dose drug, riboflavin, from capsules was dependent in some manner on the type of filler. Soluble fillers exhibited the anticipated prolonged times with increasing lubricant levels. However, the trends with insoluble fillers were less predictable. In some cases insoluble fillers were only slightly affected by the concentration of magnesium stearate. For others, such as microcrystalline cellulose, there appeared to be an ideal intermediate concentration of lubricant at which the dissolution rate was maximized. 

Fig. 8 Release of hydrochlorothiazide content from capsules, time for 60% to dissolve. All formulations filled on an instrumented Zanasi model LZ64 at the same compression force. (A) Effect of magnesium stearate concentration, microcrystalline cellulose filler, compression force 15 Kg and (B) effect of plug hardness, microcrystalline cellulose filler, compression force 21.7 Kg.

NIR was used to determine the effects of changes in magnesium stearate concentration and variations in compression pressure on tablet analysis. Various types of Avicel (microcrystalline cellulose), varying mostly in particle size, were compressed into tablets with or without magnesium stearate as lubricant by using various compression pressures. Various mathematical treatments were used to either measure the differences or obviate their effects on the analysis. 

Meanwhile, Shibata et al. [16] elaborated the reason for the effect of magnesium stearate concentration on ethenzamide dissolution rate by SEM. 

Components with a fixed concentration were Primojel (4%), oxazepam (4%), magnesium stearate (1%) and Aerosil 200R (0.2%). The components with a variable concentration were a-lactose, 6-lactose and rice starch. The concentrations of these components sum up to 90,8% of the total tablet weight, their individual concentrations can be obtained from the experimental design listed in Table 4.3 where the listed values of Xj-Xj are fractions of the total amount of 90.8% for these three components. 

Tablets of 250 mg with starch concentrations of 5%, 15% and 25% w/w respectively, were prepared. Starch and lactose were mixed for 15 minutes in a Turbula mixer at a rotation speed of 90 rpm.. Magnesium stearate (0.5% w/w) was added and mixing was continued for 2 minutes. The tablets were prepared on a single punch tabletting machine, using 9 mm flat punches. From each mixture tablets were produced at three compression load levels 157,314,472 MPa.

Glidants (e.g., colloidal silicon dioxide, talc) may need to be added to achieve desired flow properties, especially when the drug/filler ratio is relatively high. Usually, there is an optimum concentration of glidant for best flow, often less than 1% for the colloidal silicas (14,15). The following order of effectiveness of glidants has been reported for two powder systems fine silica > magnesium stearate > purified talc (16). 

In chemistry, a more relevant example might be the determination of the composition of ingredients like pseudoephedrine hydrochloride, microcrystalline cellulose, and magnesium stearate in granules of a pharmaceutical preparation. This example represents an infinite population, because the concentration of an ingredient in an aliquot of material can take on any conceivable value. 

Fig. 14 The effect of lubricant concentration (% w/w) on the measured adhesion (kPa) of hydroxypropyl methyl-cellulose films (A) Pharmacoat 606 (B) Methocel 60HG viscosity 50 ( ) stearic acid ( ) magnesium stearate ( ) calcium stearate. (From Ref. l)...

Lubricants may be classified as water-soluble or water-insoluble. The latter are generally more effective than water-soluble lubricants and can be used at a lower concentration, Common water-insoluble lubricants (which are surfactants) include magnesium stearate, calcium stearate, sodium stearate, and stearic acid water-soluble lubricants include sodium lauryl sulphate and magnesium lauryl sulphate. 

Magnesium stearate is widely used in cosmetics, foods, and pharmaceutical formulations. It is primarily used as a lubricant in capsule and tablet manufacture at concentrations between 0.25% and 5.0% w/w. It is also used in barrier creams. See also Section 18. 

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