Topical Corticosteroids

Topical corticosteroids are commonly used to treat a variety of inflammatory skin diseases. Conditions that may require a topical corticosteroid include atopic dermatitis, psoriasis, lichen planus, lichen sclerosus, and vitiligo.

Although topical corticosteroids are often used to treat the itch and inflammation of non-specific rashes, it is important to diagnose the skin condition accurately before treatment begins. These preparations can exacerbate some conditions, particularly those with an infectious component.

Conditions that should not be treated solely with a corticosteroid include impetigo, herpes simplex, molluscum contagiosum, Malassezia folliculitis, and tinea. A topical corticosteroid may be appropriate to treat the itching and local inflammation of an infectious condition if combined with a suitable antimicrobial agent. For example, many proprietary products combine an antifungal with a topical corticosteroid to treat tinea.

There are many topical corticosteroids available in Australia. These agents can be classified based on their potency, as demonstrated in Table 1.

Table 1: Potency of topical corticosteroids available in Australia

The designated potency of a corticosteroid is approximate and can be affected by many factors. For example, betamethasone dipropionate 0.05% can be considered potent or very potent depending on its formulation. Relative potency is increased when absorption is increased, and the formulation is an important determinant of absorption.

In general, corticosteroids that are formulated as an ointment are more potent. Ointments are often defined as containing 80% oil and 20% water. This high oil content means that ointments are not well absorbed and tend to remain on the surface of the skin. However, this acts as an occlusive barrier which increases penetration of the active ingredient into the stratum corneum. Ointments are also more hydrating than other topical formulations and are, therefore, beneficial in the treatment of dry skin conditions. These products are often not patient-preferred as they are greasy, difficult to spread, and may cause staining of clothing or bed linens.

Creams may be defined as containing approximately 50% oil and 50% water. This produces a less greasy product that is easy to spread and readily absorbed. Given their consistency, creams are often preferred for the treatment of large areas of skin. They are also often favored for the treatment of oozing skin conditions as they are less hydrating than ointments.

Lotions may contain insoluble particles dispersed in liquid. They should be shaken before use to ensure an even concentration is achieved. Lotions are easy to apply and can be used to cover extensive areas. They are often prescribed for use on the scalp and hairy areas as they penetrate rapidly leaving little residue. Lotions are even less greasy and occlusive than creams.

Although the formulation largely determines the degree of occlusion and absorption, external factors can also play a significant role. Occlusive dressings and the application of direct heat to the site of application can significantly increase absorption.

Topical corticosteroids are considered to be relatively safe when used appropriately. However, they can produce side effects, particularly when treatment is prolonged. Skin atrophy is one of the more common local side effects and may not be completely reversible upon treatment discontinuation. Skin atrophy may present as increased transparency of the skin, telangiectasia, striae, and easy bruising. These effects are more commonly associated with prolonged use of topical corticosteroids and application to areas where the dermis is particularly thin, such as the face.

Systemic side effects are uncommon with the use of topical corticosteroids. When they do occur, they are often associated with the use of high potency agents applied to large areas. The use of occlusion also increases the risk.

To reduce the incidence of local and systemic side effects, it is important to select an appropriate agent and counsel the patient on how to use it properly. Very potent topical corticosteroids generally should not be applied to areas of thin skin such as the face, flexures, or scrotum. The use of topical corticosteroids on the face can result in conditions such as steroidal rosacea, acne, and perioral dermatitis. Patients should also be advised to avoid inadvertently introducing the medication to the eye to prevent the development of glaucoma. Treatment duration also needs to be addressed with the patient as rebound effects can occur when treatment is stopped. Particular care should be exercised when selecting a topical corticosteroid for use in children as they are more susceptible to their adverse effects. In general, low-potency agents used for short periods are preferred in this population. Parents and carers should be cautioned about the use of corticosteroids in the nappy area as nappies can cause occlusion.

Selection of an appropriate agent should also encompass the responsiveness of the condition and the site of application. Mild corticosteroids may be used for conditions that are highly responsive to topical corticosteroids. This includes conditions such as intertriginous psoriasis, atopic dermatitis in children, and seborrhoeic dermatitis. Moderately potent agents are usually required for conditions such as psoriasis, atopic dermatitis in adults, and nummular eczema. Very potent agents should be reserved for chronic, hyperkeratotic, lichenified, or indurated lesions. Conditions that produce these effects, such as lichen planus, lichen simplex, and palmoplantar psoriasis, are the least responsive to topical corticosteroids.

The application site is also a major determiner of the degree of absorption. Absorption tends to be poor on the palms of the hands and soles of the feet. Absorption is also low from the forearms with only around 1% of applied medication absorbed. Absorption may be ten times higher from the face and up to 40 times higher from areas such as the scrotum and eyelids. These site-specific differences in skin characteristics mean that inflammatory conditions of the face and skin fold areas should generally treated with low-potency preparations, and lesions on the palms and soles will often require high potency agents.

Once the correct agent is selected, it is important that it is applied correctly. Most topical corticosteroids are applied once or twice a day. More frequent application does not improve efficacy and may increase adverse effects. Many preparations are labeled with the directions ‘apply sparingly.’ Although this may be good advice for very potent agents or for application to thin skin or very young children, applying insufficient quantities runs the risk of treatment failure. The fingertip unit (FTU) is widely recommended to assist patients in applying the correct quantity of topical preparations that are difficult to measure. An FTU is defined as the amount of cream or ointment squeezed from a standard tube along an adult’s index finger from the tip to the first crease of the finger. This equates to approximately 500mg. One FTU is an appropriate quantity of cream or ointment to treat an area the size of two adult hands held flat with the fingers together. When treating children, an adult index finger is still used to measure the quantity.