Formulation tips for the most-used topical solvents

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  • March 30, 2022
  • 3 mins of read time

Formulation tips for the most-used topical solvents

Solvents are the best allies of formulation scientists to improve the solubility of an API in its dosage form. The choice of solvent/co-solvent system matching the characteristics of your API is the first step to a successful topical drug development.

Commonly used  solvents and maximum potency recorded for topical applications - extract from the Inactive Ingredient Database as of December 2021.1

Commonly used  solvents and maximum potency recorded for topical applications: Diethylene glycol monoethyl ether 49.91% PEG 400 99% Ethyl alcohol 92.38% Isopropyl alcohol 43.90% Propylene glycol 99.98% Dimethyl sulfoxide 45.50%

However solvents often come with their own challenges. Solvent can be difficult to thicken and may destabilize your formulation especially when high solvent content is required. This can lead to suboptimal choices such as decreasing the amount of solvent in your formula, thus limiting the API drug load and its skin permeation potential.

Polymer choice plays a critical role when formulating solvent-rich media, from thickening capabilities to driving the texture of your drug. Inverse latex polymers & associative polymers exhibit particularly strong thickening & stabilizing capabilities, even with high solvent content.

Sepineo™ P 600 is at the origin of a breakthrough in formulation of high load of Dapsone through the thickening & stabilization of diethylene glycol monoethyl ether (>30%).2

Contact us for more information on formulation

Formula: qs polymer for an aqueous gel of 100 000 mPa.s, x% of solvent, water qs 100%
Process:
1. Mix the polymer + water to obtain an aqueous gel of 100 000 mPa.s.
2. Slowly add the solvent. For the concentrated powder grade high shear and/or longer 
    agitation might be necessary.

APIs often require the combination of several solvents to match their specific properties and reach the solubilisation target, as well as to limitate the risk of side-effects linked to high concentration of one solvent.

Whatever the solvents you require and their respective concentration, the polymers introduced above will help you build a robust vehicle for your API; you only need to adjust their dose to achieve your targeted viscosity.

The polymer network obtained with SEPINEO P 600 or SEPINEO PHD 100: does not require neutralization, is highly shear-resistant, is table over a wide PH range, is not impacted by the temperature, drive your final drug texture
The use of these polymers open multiple possibilities of dosage forms for you API :

The use of these polymers open multiple possibilities of dosage forms for you API :

  • Gel
  • Cream-gel: a highly versatile vehicle for stabilization of solvents and lipophilic phases without emulsifier addition.
  • O/W emulsion: increased robustness for stressful APIs or API combinations.
  • Geltrap™ Gel-in-oil emulsion: the best choice for texture-improvement even with high solvent content.

Choose your chassis
for the formulation
of topical solvents

1. Center for Drug Evaluation and Research. Inactive Ingredients in Approved Drug Products Search. FDA (As of December 2021).
2. Warner, K. S., Parashar, A. P., Swaminathan, V. & Bhatt, V. Topical dapsone and dapsone/adapalene compositions and methods for use thereof. (2015).