Topical Preparations

Introduction

In an overview, transdermal formulations aim to deliver the drug to therapeutically active levels at the target site (either local or systemic) through skin.

It has been estimated that for topical products such as creams and gels, typically only between 1% and 3% of the applied dose is bioavailable.
Bioavailability from patches is typically 30% to 70% for drugs such as buprenorphine and fentanyl.

NOTE: Topical treatments used for local effects have a decreased incidence of systemic side effects and generally provide faster relief. But, local reactions may occur as side-effects.

Formulation Options

Generally,

Semisolid formulations are selected for increased residence on the skin;
Transdermal patches are selected for extended drug delivery through the skin;
Liquid formulations are selected for a rapid short-term input of permeant into the skin.

Cream or Ointment

At work (being at a hospital pharmacy or community pharmacy), we may find certain topical products come in both cream and ointment form, such as fusidic acid cream and ointment.

Creams contain more than 20% water and up to 50% oil. They spread easily and are reasonably hydrating.
Lotions contain the most water (compared to other topicals), are more fluid than creams and can be poured. They are easy to spread on the skin and they absorb quickly.
Ointments contain the least water; 0-20% with the remainder composed of oil-based product(s). Ointments are good delivery vehicle to provide a barrier to exposure (e.g. organisms, sun) and they prevent moisture loss which helps burn and scar healing.

As a pharmacist, which product will you recommend? And more importantly, why? Factors affecting formulation type of topical therapy.

Depending on the lesion type,

For a wet, vesicular or weeping lesion, a 'wet' (usually aqueous-based) formulation is generally preferred, such as cream, lotion or gel.
For a dry, thickened scaly lesion, a 'dry' (usually fatty) formulation is preferred, such as an ointment or paste.

The skin site to be treated can affect the selection of the vehicle.

For hairy areas, lotions, gels or sprays are usually preferable.
For intertriginous areas (sites where skin may touch or rub such as the axilla of the arm), creams or lotions are usually preferred.

NOTE: Beyond the broad nature of the vehicle, specific formulation components may be required, dependent on the physicochemical properties of the drug (e.g. the drug pKa and the need for a buffer, the stability of the drug and the need for an antioxidant), clinical considerations (e.g. intact or broken skin, duration of use) and to improve patient adherence.

Search This Blog

Rx Note