Fundamental Principles for Current Topical Formulations

Topical formulations are applied directly to the skin surface, offering significant benefits in localized treatment. The main advantages of this method include:

• It allows the administration of a higher drug dose directly at the affected site.
• It results in a reduction of side effects and systemic Oral non-steroidal anti-inflammatory drugs (NSAIDs), such as diclofenac, can relieve discomfort and reduce redness in skin affected by rosacea. Although rare with use, potential serious adverse effects of these medications include peptic toxicity in other organs, compared to systemic treatments. steroids.

However, there are certain disadvantages associated with topical preparations:

• The application process can be prolonged.
• The treatment regimen is sometimes complex, especially when multiple different formulations are prescribed.
• Applications can be uncomfortable or difficult for the patient to manage.

A topical formulation essentially consists of a vehicle vehicle or base, which can be optimized for a specific type of body site or dermatological condition. The product design may focus on being highly moisturizing or maximizing the ability of an active ingredient, usually a medication, to penetrate the skin.

The amount of active ingredient that is ultimately absorbed through the skin depends on several crucial factors:

• Skin thickness significantly influences this: thinner skin absorbs a greater amount than thick skin. This thickness varies depending on the body region, the individual's age, and the existing skin disorder.
• Integrity of the skin barrier function: this function can be compromised or altered by conditions such as dermatitis, , Ichthyosis, dermatitis, ichthyosis, or by the use of keratolytics keratolytic agents (e.g., salicylic acid). When the barrier is altered, more medication can be absorbed than through healthy, intact skin.
• Absorption of the active ingredient increases in areas presenting obstruction, occlusion, such as skin folds, under dressings, or when using an ointment formulation. vehicle reactions. or grease base.
• The molecules Small molecules cross the skin more easily than those of larger molecular size.
• Lipophilic compounds demonstrate better absorption than hydrophilic compounds..
• Higher concentrations of the active ingredient generally result in greater penetration compared to lower concentrations.
• Other components present in the formulation can interact with each other, modifying the potency or absorption rates upward or downward.

It is important to note that even small modifications in the composition of a formulation can cause notable differences in the clinical effectiveness of a topical medication.

Calculating the Required Amount in Topical Formulations

Determining the appropriate amount of topical medication to prescribe can be a challenge even for the most dermatologist experienced dermatologist. This amount depends on several key parameters:

• The type of vehicle selected.
• The thickness with which the product is applied.
• The total extent of the body surface area to be treated.
• The frequency of application.
• The total duration of the prescribed treatment cycle.

Generally, it is estimated that 1 gram (g) of lotion cream covers approximately an area of 10 cm² on the skin; ointments tend to spread slightly more upon application.

The fingertip unit (which corresponds to about 0.5 g) serves as a practical guide to estimate the amount of cream or ointment required to treat a specific area over a given period. A single fingertip unit is sufficient to cover the palmar surface of one hand (one side of two flat hands), while one gram covers both sides of both hands of the patient.

To cover the entire body of an adult in a single application, an amount ranging between 20 and 30 grams of cream or ointment is usually required.

Vehicles Used in Topical Formulations

Topical formulations typically consist of an active ingredient, which can be a medication, a drug, or a botanical extract, and a vehicle. vehicle. This vehicle usually includes a water, oil, alcohol, or propylene glycol base, mixed with essential components such as preservatives, emulsifiers, absorption enhancers, and added fragrances.

Below are details of different types of formulations. It is important to note that manufacturers may interpret and label these classifications variably; therefore, a preparation with similar characteristics might be named a loción, gel lotion.

Topical Formulation Classification

Formulation	Description	Image
Solution	A liquid preparation, generally water or alcohol-based, that incorporates a powder powder dissolved or in suspension.
Lotion	Generally considered more viscous than a solution, it is more likely to contain a mixture of oil, water, or alcohol. Some whipped lotions may separate over time, requiring shaking before application to achieve a uniform suspension.
Cream	Thicker than a lotion, a cream maintains its shape. It is typically an emulsion with an approximate 50/50 proportion of oil and water. Its formulation requires preservatives to ensure a prolonged shelf life and frequently provides a moisturizing action.
Ointment	A semi-solid preparation with very low or no water content (often 80% oil). It possesses greasy and sticky characteristics, acting as an emollient, or a soothing, protectant, and occlusive. occlusive agent contact . It does not require preservatives, which reduces the risk of contact.
Miconazole	Ointment formulation.
Gel formulation	Paste.
Aerosol foam or spray o spray	A liquid solution that is dispensed via a pressurized system with a propellant.
Powder	Solid dosage form firm, such as talc (mineral origin) or cornstarch (vegetable origin).
White	Sticks used as antiperspirants or sunscreens. Some solid bases are designed to melt upon reaching body temperature, like a suppository.
Solid formulation patch	Transdermal patch.

Patch formulation.

In the cosmetic and pharmaceutical fields, manufacturers also use other descriptors for their preparations, such as emulsion, paint, suspension, milk, syrup, collodion, balm, and mist. It is common for final formulas to incorporate ingredients dispersed or combined in more than one type of base vehicle.

The proper selection of the vehicle or base for a topical medication is fundamental and depends directly on several factors, including the specific nature of the skin condition being treated and the desired physicochemical characteristics for active delivery.

Crucial Considerations in the Formulation and Application of Topical Treatments The preparation of a pharmaceutical mixture by a pharmacist is often called an. extemporaneous preparation . The initial components, usually derived from natural sources, are called galenicals.

and can be incorporated into a vehicle or an already commercialized product.

The correct choice of vehicle or base is fundamental to optimizing the clinical efficacy of any skin treatment applied to the skin and its site.

Influence of the Nature of the Dermatosis on Topical Formulation

• The specific skin condition dictates the most appropriate texture and consistency for the topical formulation: creams, In the case of weeping or oozing skin conditions: creams,.
• lotions, and pastes with drying properties are preferable. cellsFor dry and.
• scaly skin conditions: ointments and oils are more suitable.
• If skin inflammation exists: it is recommended to start with wet compresses and baths, followed by the application of creams or ointments.

To treat cracks and sores: gentle applications should be made, strictly avoiding the use of alcohol and acidic preparations.

Impact of Skin Location on Formulation Choice

• The anatomical area where the skin problem occurs is also a determining factor for selecting the appropriate consistency: Palms and soles: In these thick areas, an ointment or cream can be chosen.
• Skin folds: The use of creams or lotions is recommended, as ointments are excessively occlusive for these spaces. Hairy areas: Generally, the most effective option is a lotion, solution, gel, or foam.
• Mucosal surfaces: Extreme caution must be exercised when prescribing formulations, choosing those that are non-irritating so as not to aggravate already eroded surfaces. Special Circumstances in Topical Administration.
• Considerations for Topical Formulations in Newborns mucosaAlthough the skin barrier capacity in full-term newborns is comparable to that of older children and adults, this function is significantly compromised in premature babies.

Furthermore, the baby's body surface area is proportionally much larger compared to an adult. Since vital organs such as the liver, kidneys, circulatory system, and central nervous system have not reached their full development, topically

applied absorption of medications has a higher probability of inducing side effects and systemic toxicity.

Topical Formulations During Pregnancy and Lactation.

As with orally administered drugs, certain topical medications may not be safe during gestation and the lactation period. These include: topically Dithranol.

Salicylic acid

Medications are stratified according to the potential risk they represent. The FDA classification system is commonly used; however, the pregnancy categories used in New Zealand are detailed below for reference:

• Category A
• Dithranol
• Drugs that have been taken by a large number of pregnant women and those of reproductive age without proven evidence of an increase in the prevalence of
• Salicylic Acid

malformations

or other direct or indirect adverse effects observed in the fetus.

Category B1 vascular Medications that have been administered only to a limited number of pregnant and fertile women, without an increase in the frequency of.

malformations

or other direct or indirect harmful effects on the human fetus being detected. Animal studies[1] have provided no evidence of an increase in the occurrence of fetal harm. malformation Category B2.

Drugs that have been taken only by a small group of pregnant and fertile women, with no increase observed in the rate of malformations or direct or secondary damage to the human fetus. Animal studies[1] may be insufficient or non-existent, but available data do not indicate a higher occurrence of fetal harm.

Category B3.

Medications taken only by a limited number of pregnant women and those of reproductive age, without an increase in the incidence of malformations or other direct or indirect harmful effects on the human fetus being documented. However, animal studies[1] have shown evidence of a higher incidence of fetal harm, the relevance of which in humans is still considered uncertain.

Category C.

Drugs that, due to their pharmacological effects, have caused or are suspected of causing adverse effects in the human fetus or the

neonate neonate, without causing malformations. It is important to note that these effects may potentially be reversible.

Category D

Medications that have caused, or are suspected of having caused, or can be foreseen to cause an increase in the incidence incidence.

of human fetal malformations or damage that is irreversible. Furthermore, these drugs may manifest other adverse pharmacological effects.

Category X.

Drugs whose risk of causing permanent harm to the fetus is so high that their use is strictly contraindicated during pregnancy or when there is a possibility of pregnancy occurring.

• Practical Recommendations for the Use of Topical Agents

Topical steroids and.

1. toxicity emollients Emollients.
2. are most effective when applied to slightly damp skin. Therefore, the optimal time for their application is within three minutes after taking a bath or shower. Steroid application should be restricted only to actively affected areas. If you have been prescribed an additional emollient, wait a few minutes to ensure complete absorption of the topical steroid before spreading the emollient extensively.
3. It is common for patients to perceive a stinging sensation on the face when applying products, especially if the skin is damp at that moment. Generally, waiting about 20 minutes significantly reduces this discomfort.
4. While stinging is common with lotions and creams, it occasionally also occurs with ointments. Changing the formulation (the product consistency) instead of the active ingredient could solve this inconvenience. In some cases, it is advisable to tolerate the stinging, as it is usually brief. After several applications with effective treatment, skin improvement usually mitigates or eliminates this sensation.
5. To reach hard-to-access areas, such as the back, it is recommended to use specific applicators for body lotions.

The official information and primary source for these prescription medications, including their approved uses and risk details, reside in the data sheets approved by New Zealand. It is advisable to review the individual New Zealand data sheet available on the Medsafe website.