Development and formulation of wax-based transdermal drug delivery systems

Topical and transdermal formulations are promising platforms for the delivery of drugs. A unit dose topical or transdermal drug delivery system that optimises the solubility of drugs within the vehicle provides a novel dosage form for efficacious delivery that also offers a simple manufacture technique is desirable. This study used Witepsol® H15 wax as a abase for the delivery system. One aspect of this project involved determination of the solubility of ibuprofen, flurbiprofen and naproxen in the was using microscopy, Higuchi release kinetics, HyperDSC and mathematical modelling techniques. Correlations between the results obtained via these techniques were noted with additional merits such as provision of valuable information on drug release kinetics and possible interactions between the drug and excipients. A second aspect of this project involved the incorporation of additional excipients: Tween 20 (T), Carbopol®971 (C) and menthol (M) to the wax formulation. On in vitro permeation through porcine skin, the preferred formulations were: ibuprofen (5% w/w) within Witepsol®H15 + 1% w/w T; flurbiprofen (10% w/w) within Witepsol®H15 + 1% w/w T; naproxen (5% w/w) within Witepsol®H15 + 1% w/w T + 1% C and sodium diclofenac (10% w/w) within Witepsol®H15 + 1% w/w T + 1% w/w T + 1% w/w C + 5% w/w M. Unit dose transdermal tablets containing ibuprofen and diclofenac were produced with improved flux compared to marketed products; Voltarol Emugel® demonstrated flux of 1.68x10-3 cm/h compared to 123 x 10-3 cm/h for the optimised product as detailed above; Ibugel Forte® demonstrated a permeation coefficient value of 7.65 x 10-3 cm/h compared to 8.69 x 10-3 cm/h for the optimised product as described above.

An investigation into the formation of wax emulsion

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The development of a wax layer on the interior wall of a circular pipe transporting heated oil

In this article we develop a simple model to describe the evolution of a depositional wax layer on the inner surface of a circular pipe transporting heated oil, which contains dissolved wax. When the outer pipe surface is cooled sufficiently, the growth of a wax layer is initiated on the inner pipe wall, and this evolves to a saturated steady state thickness. The model proposed is based on fundamental balances of heat flow from the oil, into the wax layer, and across the pipe wall. We present an analysis of the model, examine a relevant asymptotic limit in which the full details of the solution to the model are available and develop an efficient numerical method (based on the method of fundamental solutions) for producing approximations of the model solution. The mathematical structure of the model is that of a free boundary evolution problem of generalised Stefan type. © The Author, 2014.

The development of a wax layer on the interior wall of a circular pipe transporting heated oil

In this article we develop a simple model to describe the evolution of a depositional wax layer on the inner surface of a circular pipe transporting heated oil, which contains dissolved wax. When the outer pipe surface is cooled sufficiently, the growth of a wax layer is initiated on the inner pipe wall, and this evolves to a saturated steady state thickness. The model proposed is based on fundamental balances of heat flow from the oil, into the wax layer, and across the pipe wall. We present an analysis of the model, examine a relevant asymptotic limit in which the full details of the solution to the model are available and develop an efficient numerical method (based on the method of fundamental solutions) for producing approximations of the model solution. The mathematical structure of the model is that of a free boundary evolution problem of generalised Stefan type. © The Author, 2014.