Antimicrobial property of Picralima nitida stem bark extract in cream formulations

The effects of formulation variables on the antimicrobial activities of the basic fraction (BF) of the methanol extract of the stem bark of Picralima nitida Stapf. Th. & H. Durrant (Apocynaceae) in cream preparations were studied using a 23 factorial experimental design. The individual and interaction effects of nature of humectant (N), concentration of humectant (C), and time of storage of cream preparation (S) on the effectiveness of the BF cream preparations, as measured by the diameter of zone of inhibition (mm) against Staphylococcus aureus and Microsporum canis, were evaluated. The effects of the variables depended considerably on the amount of BF in the formulation. The nature of humectant (N) generally had the highest effects on the antimicrobial activity of the creams with a positive increase in activity with changes from glycerin to propylene glycol. On the other hand, changing the concentration of humectant (C) from a "low" to a "high" level (from 5% to 10%, w/w) in the formulation also general...