Surfactants dissolution rate increase

Concentrations of polysorbate 20 well in excess of the CMC have been used by Collett and Rees in their studies on salicylic acid dissolution [10,19]. Dissolution rates were measured over a pH range from 1.0 to 4.0 the dissolution rate increases very slowly above 12% surfactant (Fig. 7.4) but there was no evidence of a decreased dissolution rate such as found by Parrott and Sharma [20], e.g. above... 

The effects of surfactant on the solubility and dissolution rate of poorly soluble drugs are well characterized. In general, the surfactant increases both solubility and dissolution rate even if the increment in dissolution rate is less pronounced due to the low diffusivity of the drug loaded into the micelle [9-16]. 

If has been observed fhaf by adsorbing surfactants onto the crystal surfaces of poorly water-soluble drugs, dissolution rate can be enhanced. Chen et al. " showed that the dissolution rate of Cl-1041, a poorly water-soluble compound, in 0.1 N HCl may be affected by the surfactant Tween 80. The effects of surfactant are complicated, and many factors are involved. Above the CMC of Tween 80, the adsorption of the surfactant onto the crystal surface may inhibit crystal nucleation on the surface, and causes the dissolution rate to increase. By adsorbing a very small amount of poloxamer onto the hydrophobic drug particle surface. 

It is not the aim of this article to evaluate formulation aspects that may influence dissolution of drugs from dosage forms. However, it suffices to mention that dissolution rates of drug substances or drug release from formulated products may be influenced (increased or decreased) by factors such as assay selection, the presence of surfactants, polymorphic modification, and by the use of water-soluble carriers in solid dispersions. 

Nature of compounds. No correlation was found between Dr and Ds of six salts of ursodeoxycholic acid (UDCA). Although Ds showed that the salts had smooth surfaces, their Dr values were high. UDCA acted as a surfactant to increase the dissolution rate. Similarly, surfactant properties of diclofenate anions were found responsible for Dr being higher than Ds. " ... 

Surface-active agents have been widely shown to enhance drug dissolution rates. This may be due to wetting effects, resulting in increased surface area, effects on solubility and effective diffusion coefficient or a combination of effects. Consequently surfactants have been included in tablet and capsule formulations to improve wetting and deaggregation of drug particles and thus increase the surface area of particles available for dissolution. 

Examples of the adsorption of dmgs and excipients on to solid surfaces are found in many aspects of dmg formulation, some of which, for example the adsorption of surfactants and polymers in the stabilisation of suspensions, are considered elsewhere in this book (see section 7.4). An interesting approach to the improvement of the dissolution rate of poorly water-soluble dmgs is to adsorb very small amounts of surfactant on to the drug surface. For example, the adsorption of Plutonic F127 onto the surface of the hydro-phobic dmg phenylbutazone significantly increased its dissolution rate when compared with untreated material."... 

Bioavailability of triamterene has been studied in healthy human subjects.59 62 65 79 The bioavailability of triamterene was found to be 52%, corresponding to absorption of 83%, in a study done in six volunteers after intravenous administration of the drug.62 Another study reported that triamterene bioavailability from capsules was poorer and more variable than that from suspension.65 Effect of various vehicles and vehicle volumes on oral bioavailability of triamterene has been investigated.80 Addition of a combination of a surfactant and carbonate or bicarbonate as diluents to a triamterene gelatin capsule is reported to result in better bioavailability of the drug.81 When both calcium carbonate and cetylpyridinium chloride were present in a triamterene capsule the dissolution rates were greatly increased over triamterene capsules containing neither diluent or either... 

Shellac used as a tablet coating, upon aging, can slow the drug dissolution rate. Surfactants may affect drug dissolution in an unpredictable fashion. Low concentrations of surfactants lower the surface tension and increase the rate of drug dissolution, whereas higher concentrations of surfactants tend to form micelles with... 

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