Formulation and Assessment of the Efficacy and Stability of an Ointment Containing Ocimum americanum L. Extract

Background

Ocimum americanum L. is an annual herbaceous plant used to manage pain and inflammation. Lack of standard dosage forms, and safety and efficacy data potentially exposes users of this medicinal plant to the risk of toxic or sub-therapeutic effects, as well as drug-herb interactions.

Objective

The study developed a standard dosage form containing O. americanum extract and assessed its anti-inflammatory efficacy and stability.

Methods

The fusion method was used to formulate an ointment comprising acetone extract, beeswax, and soft-paraffin. Formulation optimization involved the application of Box-Behnken Design (BBD) to design an experiment whose input variables were %beeswax and %soft-paraffin and its melting temperature. Output variables were drug release and viscosity which were quantified using a vertical diffusion cell (VDC) and stanhope-seta viscometer, respectively. Wistar albino rats were used in carrageenan-induced rat hind paw edema (n = 6/test, positive and negative control) to assess the anti-inflammatory effect. Stability studies comprised assessment of spreadability, thin layer chromatograms (TLC), and microbial growth in ointment batches stored at 25 $\pm$ 2℃/ 60 $\pm$ 5% RH and 40 $\pm$ 2℃/ 75 $\pm$ 5% RH.

Results

Temperature and %beeswax significantly influenced drug release (P = 0.0024). Optimal drug release and viscosity were obtained at 5.4% beeswax, 89.6% soft-paraffin melted at 58℃. The predominant drug release mechanism was Higuchi (R² = 0.967 $\pm$0.023), which implied longer contact between formulation and skin favours drug diffusion. Inhibition of edema by the ointment was comparable to 1% (w/w) diclofenac gel (t = 2.1; CI = (-8.29)-1.15), and both differed significantly with negative control (t = 11.3 and 13.4; CI = 14.5-23.9 and 18.1-27.5 respectively). Insignificant changes in spreadability (P = 0.112), absence of new spots on chromatograms, and deficiency of microbial colonies on agar plates implied physical, chemical, and microbial stability, respectively.

Conclusion

A formulated ointment containing O. americanum extract exhibited predictable and stable drug release characteristics to produce anti-inflammatory activity. The ointment formulation can potentially be considered as an effective option in management of peripheral inflammation.