Dispersing agents poloxamers

Fig. 12 Substances used for complex formation and nanoparticles, (retinoic acid) All-trans retinoic acid, (PLA) poly(-L-arginine), (PLH) poly(-L-histidine), (PLL) poly(-L-ly-sine). As dispersing agent a tri-block copolymer was used. It consisted of ethylene oxide and propylene oxide (Poloxamer 188). Reprinted with permission from [142]. Copyright 2000 American Chemical Society...

Dispersion of the powder in the vehicle. This requires adequate wetting of the powder (external and internal surfaces) by the liquid vehicle, necessitating the use of a wetting/dispersing agent, mostly a nonionic surfactant (such as poly-sorbates) or polymeric surfactant (such as Poloxamer). This process is described in detail in Chapter 7. 

Poloxamer 188 has also been used as an emulsifying agent for fluorocarbons used as artificial blood substitutes and in the preparation of solid-dispersion systems. 

Many drug carriers are made of hydrophobic materials such as lipids and poly(butyl cyanoacrylate). It will be thermodynamically unstable for submicron particles made of these materials to remain dispersed in an aqueous environment such as blood circulation. Surfactants or block co-polymers are therefore routinely included in these formulations to prevent particle aggregation. Studies showed that a number of these agents, most noticeably the nonionic surfactants such as polysorbates (also known as Tweens) and Tritons and block co-polymers such as poloxamers (also known as Pluronics), may inhibit the ABC transporters [97-99]. As previously discussed, ABC transporters interact with their substrates in the lipid bilayers of the plasma membrane. Surfactants can disrupt the arrangement of the lipid bilayer expressing the transporters and subsequently inhibit their drug efflux activities [97, 100]. It... 

Typical excipients used in parenteral suspensions include surfactants that are used to stabilise emulsions and suspensions as wetting agents (polysorbate 80, poloxamer), as micelle makers for the preparation of solubilisations and to influence the flocculation and deflocculation behaviour of a dispersed system (carmellose sodium, polyvidone). Paren-terally used surfactants in high concentrations are toxic and may cause venous irritation and occasional thrombophlebitis. However, these high concentrations are not necessary to formulate stable parenteral suspensions. 

This short chapter deals primarily with the effect of surfactants on the properties of suspensions. Suspensions can be prepared without surfactants, there being an increasing use of polymers for stabilizing dispersions of solids in liquids. We will restrict discussion here to the effects of conventional surface-active agents but will deal also with the use of surface-active polymers such as the poloxamers, as these bridge the gap between two very large subjects. The emphasis of the chapter is towards pharmaceutical suspensions. 

Poloxamer, PVP, copovidone and PEG are suitable solubilizing agents for solid dispersions. Soluplus enable hot-melt extrusion to be carried out at low tanpera-ture without the addition of other excipients such as plasticizers [52]. Some hyper-branched polymers (e.g. Hybiane , Eig. 11.5) of reduced Tg are also suitable for... 

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