Batch Variation of Magnesium Stearate and its Effect on the Dissolution Rate of Salicylic Acid from Solid Dosage Forms

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Abstract
The effects of different batches of magnesium stearate on the release of salicylic acid from capsules and from a compacted formulation have been investigated. The results indicate that retardation of salicylic acid release becomes independent of the particle size of magnesium stearate when the blending of the two substances prior to encapsulation or compaction is prolonged for a sufficient time. Variation in the release rates observed after prolonged blending times have been shown to exhibit a rank order correlation with the different hydrophobicities of the batches of magnesium stearate as indicated by the results of contact angle measurements on drops of dissolution medium on compacts of this lubricant. Determination of the surface tension of an aqueous extract of each batch of lubricant has indicated that water-soluble, surface-active impurities may be responsible for this apparent variation in the degree of hydrophobicity and hence for the change in the release rate of salicylic acid from solid dosage forms when they are manufactured with different batches of magnesium stearate.
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