Purpose: To develop and characterize solid lipid nanoparticle (SLN) systems containing dextran sulfate or sodium alginate as anionic polymers for the delivery of clindamycin phosphate as a model hydrophilic cationic drug.

Methods: A multi-level factorial design was used for the preparation and optimization of clindamycin SLNs. Polymers (dextran sulfate and sodium alginate), Tween 80, and Pluronic F68 were chosen as the independent variables. The SLNs were prepared using stearic acid as the lipid matrix by an emulsion congealing technique with cold homogenization. Particle size and drug loading were evaluated as the primary responses. The morphology and drug release rate of the selected formulations were also determined.

Results: The results revealed that incorporation of anionic polymers increased drug loading of the SLNs. Dextran sulfate had a greater effect on drug loading, increasing it from 1.32 to  18.19 %, compared to the 6.73 % achieved using sodium alginate. Dextran sulfate also reduced drug release rate by half compared with sodium alginate, probably due to the higher charge density, lower molecular weight and lower branching density of the ionic polymer.

Conclusion: Incorporation of anionic polymers can increase the loading of clindamycin phosphate into SLNs. Drug release from SLNs is also dependent on the polymer type.