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Contrary to popular belief, not all generic and branded topical preparations are created equal in terms of efficacy and tolerability, in part due to the crucial differences in the vehicle used.
Orlando, Fla. - Contrary to popular belief, not all generic and branded topical preparations are created equal in terms of efficacy and tolerability, in part due to the crucial differences in the vehicle used.
According to an expert who spoke at the Orlando Aesthetic and Clinical Conference, generic topical preparations are often far from equal from their branded topical counterpart products and therefore, physicians should be cautious in their choice of topical preparations and formulations in their patients.
“The type of vehicle used in a topical preparation can often be the key to treatment success, or its failure,” says Leon H. Kircik, M.D., clinical associate professor of dermatology, Indiana University School of Medicine, Mount Sinai Medical Center, Physicians Skin Care, Louisville, Ky. “Not all topical preparations are created the same in respect to the vehicle used and it is not uncommon that the use of generic preparations can result in a decreased efficacy of the active agent as well as lead to adverse events when compared to branded topical products.”
The hydrophobic stratum corneum is a formidable impassable barrier to topical drugs, fortified by its intercalating mix of insoluble proteinaceous dead corneocytes and lipids, Dr. Kircik says, which places special demands on the compound intended for treatment.
Transport across the stratum corneum is largely achieved through passive diffusion, the efficacy of which is in part dependent on the integrity of the skin as well as the physiochemical characteristics of the drug and the vehicle used in the topical preparation.
“A good vehicle will have many different attributes, which together are intended to facilitate and help optimize the penetration, permeation and absorption of the active ingredient intended for topical treatment. Regardless of how good your active drug is, if you don’t have a good chauffeur and your vehicle doesn’t transport well, you are not going to be able to go through the stratum corneum well,” Dr. Kircik says.
Designing the appropriate vehicle is crucial and involves a mosaic of different factors, he says. This includes understanding the stratum corneum structure and its function to optimize delivery to the target site, efficiently depositing the drug on the skin with even distribution, optimal release and delivery of the drug to the target site, sustaining therapeutic drug level in the targeted tissue - allowing for the intended pharmacological effect - as well as being cosmetically acceptable and tolerable for the patient.
The epidermis is an active barrier and the largest drug metabolizing tissue in the body. According to Dr. Kircik, ideal vehicles are drug-specific and each formulation should be customized based on the active ingredients and treatment target site. Here, manufacturers must overcome key challenges, he says, including the metabolism of the topical drug such as witnessed in the biotransformation of the applied compound in the skin.
“Biotransformation can be both a challenge and an opportunity for topical drug formulators. Formulators must also consider the physical changes that occur as a formulation is applied to the skin.
“Volatile components such as water, alcohol and propellants all eventually evaporate, thereby concentrating the active drug and non-volatile excipients. Residual components become mixed with the hydrolipidic film on the skin, creating a ‘secondary formulation,’ which is how the drug is typically delivered into the skin,” Dr. Kircik says.
Penetration enhancers such as propylene glycol and others are also often used in topical preparations and can help facilitate and expedite the pathway of the drug to the target site. When used in high concentrations, however, propylene glycol can irritate the skin, which can lead to issues of compliance, Dr. Kircik says. This underscores the need for an appropriate concentration and perfect balance of this compound in the vehicle.
The quality of the transport of the vehicle is very important and a pivotal part of therapeutic success of topical preparations. Differentiating between generic versus branded topical products, however, is becoming more and more difficult today, Dr. Kircik says, because there is more than one generic preparation on the market and often, one does not know whether the appropriate vehicle is being used in a given generic topical preparation.
“Many physicians may often prescribe generic topical preparations because they believe that the substitute vehicle is at least as good and effective as those contained in branded topical products,” he says. “Unfortunately however, this is very often not the case, as substitute generics can have a bioequivalence variability of up to 45 percent compared to branded products.”
The branded topical preparations that physicians prescribe are also often substituted by the pharmacist with generic topical preparations. This may result in less than optimal treatment outcomes for the patient due to the substandard vehicle used in generic preparations.
“Physicians should be wary of the topical preparations they prescribe and that their patients ultimately use in order to maximize treatment outcomes,” Dr. Kircik says.
Disclosures: Dr. Kircik reports no relevant financial interests.