Topical Drug Development

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How Important is the Right Formulation for
Topical Drug Development?
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Topical Formulations

• Topical formulations are becoming increasingly
  popular in the pharmaceutical industry.
• Not only have they allowed the delivery of the
  drug substance to a specific site, but they also
  avoid fluctuations in drug levels, inter and
  intra-patient variations, and improve the
  patients compliance with the treatment.
• In a topical formulation, the skin acts as a
  perfect medium for the delivery of the drugs
  having both local and systemic effects, but also
  acts a mechanical barrier for the penetration of
  some.

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• This is so because the ingredients in the topical
  applications not only react amongst themselves,
  but also with the skin of the patient.
• For example, the drug substance used in a
  psoriasis treatment may be effective simply due
  to the hydrating or soothing effects of
  the formulation. Whether the molecule maintains
  its purity, potency, and delivery to the right
  target site may be masked by the ingredients that
  surround it.
• Both the mechanical barrier properties of the top
  layer of skin and the physicochemical properties
  of the drug affect the transportation of the drug
  substance from the formulation to the site of
  action.

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Thus, to have the desired benefit from topical
applications, their right formulation is
absolutely essential. Even a small change in the
formulation of the topical drugs can make a huge
difference in their efficacy.
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• Therefore, with topical applications, the right
  formulation is as important as the molecule
  itself to ensure that the drug substance is
  delivered to the right target site and maintains
  the dosage integrity, drug transport, and active
  duration.
• Moreover, in addition to the ingredients in the
  formulation, factors like pH, viscosity, and the
  relative amounts of oil, water, surfactants,
  stabilizers, droplet size, ionic nature, and the
  method of preparation can also influence skin
  absorption and efficacy.

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This makes preformulation studies and careful
selection of excipients highly important in the
formulation of topical applications.
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The right formulation and selection of excipients
for topical application is extremely important as
it may alter the following

• Its ability to permeate through the skin
• Its stability through shelf life
• Its ability to not metabolize in skin
• Its ability to stay dissolved at right
  concentrations
• Its capability to achieve the desired release
  rate

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• Besides the excipients, attention must be given
  to the choice of permeation enhancers in the
  early stages of topical drug development.
• The bioavailability of the drug in the desired
  location, i.e. the epidermis or dermis must be
  considered when choosing the right excipient and
  permeation enhancer.
• An excipient that forms a depot of the drug
  concentration in the dermis or epidermis may not
  be ideal for the formulation of a topical drug.

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• All the more, the pH of the formulations,
  particularly how they react to the pH factors in
  different layers of the skin, is very important.
• To conclude, the right formulation for
  topical drug development is determined by the
  properties of the drug substance, excipients, and
  the intended target area.
• Formulations can be improved by considering both
  the properties of the skin and the drug
  substance/excipients. And all this can be
  analyzed during skin-permeation studies.

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The right formulation and delivery method in
topical drug development can pass or fail the
drug substance. Getting the preparation right
from the formulation development services experts
saves money and time.
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