Prof. Dr. Johann W. Wiechers Independent Consultant for Cosmetic Science JW Solutions, Gouda, The Netherlands Visiting Professor at The School of Pharmacy University of London, London, UK Technical Advisor Cosmetics & Toiletries Formulating for Better Efficacy
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Prof. Dr. Johann W. WiechersIndependent Consultant for Cosmetic ScienceJW Solutions, Gouda, The NetherlandsVisiting Professor at The School of Pharmacy University of London, London, UKTechnical Advisor Cosmetics & Toiletries
Formulating for Better Efficacy
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The answer to better efficacy is simple, don’t you think?
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The answer to better efficacy is simple, don’t you think?
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Can technology provide better answers in financially challenging times?
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“Formulating for Better Efficacy” is a structured approach to formulation design
1. Selection of the drug / active ingredient
2. Selection of the emollient
3. Selection of the emulsifier
4. Selection of adjuvants
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“Formulating for Better Efficacy” is a structured approach to formulation design
1. Selection of the drug / active ingredient
2. Selection of the emollient
3. Selection of the emulsifier
4. Selection of adjuvants
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Step 1: Can my drug / active penetrate the skin in sufficient amounts?
Select only drugs/ actives that:- MW < 1000, ideally <500- octanol/water partition coefficient of 10-100- non-ionized- melting point below 40 °C- high dipole moment
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Step 1: Can my drug / active penetrate the skin in sufficient amounts?
Calculate the permeability coefficient using the Potts – Guy equation:
Step 1: Can my drug / active penetrate the skin in sufficient amounts?
Input = Jss = kp · ΔC
Output = Cl · CT
Delivery gap = MEC / CT, ideally ≤ 100
ClC k = C p
TΔ⋅
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“Formulating for Better Efficacy” is a structured approach to formulation design
1. Selection of the drug / active ingredient
2. Selection of the emollient
3. Selection of the emulsifier
4. Selection of adjuvants
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An emollient serves two important functions related to skin delivery
High absolute solubility of the drug in the formulation to ensure that enough is present to reach minimal effective concentrations at target site
Low relative solubility of the drug in the formulation, relative to that in the stratum corneum to ensure a good driving force for the drug to penetrate the stratum corneum
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“Formulating for Efficacy” optimises these two contradictory requirements…
High absolute solubility in formulation:polarities drug and formulation the same
Low relative solubilities in formulation:more soluble in stratum corneum than in formulation, therefore:polarities drug and stratum corneum the samepolarities drug and formulation different
How to cope with such contradiction?
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“Formulating for Efficacy” identifies the optimal ‘polarity’ of your formulation
driving forcepenetrant
Optimal polarities of formulation
solubilitypenetrantsolubilitypenetrant
morehydrophilic
polarity penetrant
+ PPG- PPG morelipophilic
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PPG stands for the penetrant polarity gap…
…and is the difference in “polarity” between drug and stratum corneum
The bigger the PPG, the smaller the skin delivery
Both optimized formulation polarities are equally good from a delivery point of view
Optimized polarity of formulation can be calculated: