Chapter 29. Application of drugs to the skin, nose and ears
LEARNING OBJECTIVES
Topical preparations
At the end of the chapter the reader should be able to:
• list the different bases used for topical preparations
• identify the relevant base to use for a medication, depending on the acuteness of the skin condition
• identify the main treatments for common skin diseases
• list the potential sensitizers used in topical preparations
• describe the action of the different potencies of topical corticosteroids
Application of skin preparations
At the end of the chapter, the reader should be able to:
• demonstrate the correct way to apply the different forms of topical medications
• describe the recognized methods for applying the prescribed amounts of corticosteroids
• identify the drugs that may cause a reaction on the skin
The skin
When drugs are applied to the skin, the term topical treatment is often used. A topical application generally consists of an active application, the drug, in a base or vehicle. The type of topical application that is used depends on the type and stage of the skin disease, and it is just as important to use the correct base as it is to use the correct active agent. The base consists of one or more of the following: powder, water and grease. The most commonly used bases or vehicles are as described in the following sections.
Ointments
The distinction between modern ointments and creams is no longer so obvious because of the wide range of bases that are used for both ointments and creams. Ointments are generally more ‘greasy’ and creams are thinner and consist of emulsions of various types.
Ointment and cream bases are nowadays classified as:
• hydrocarbon bases
• fats and fixed oil bases
• absorption bases
• emulsifying bases
• water-soluble bases.
Water-soluble ointments: these bases have the advantage that they do not stain.
Emulsifying ointments: these emulsify with water. An example is lanolin (hydrous wool fat), which is still very commonly used. Prolonged use of non-medical-grade lanolin in some patients can lead to sensitization to the lanolin. These bases are useful for retaining active agents in contact with the skin for as long as possible.
Non-emulsifying ointments: these do not mix with water. The paraffins form the basis of most of the very greasy ointments. With the addition of a suitable active agent they are a good treatment of chronic, dry skin disorders such as chronic atopic eczema, psoriasis, ichthyosis (dry skin with fish-like scales) and for common disorders such as chapping of the hands.
Creams
Creams are emulsions which are either water dispersed in oil (i.e. oily cream) or oil dispersed in water (i.e. aqueous cream). The latter are generally very acceptable to patients cosmetically and are used to moisten and soften the skin surface. Appropriate active agents can be added. Barrier creams protect the skin against physical agents such as water or sunlight.
Pastes
Pastes can be greasy or drying and they contain a large amount of powder. They are particularly useful for localized lesions: for example, in psoriasis. In this disorder it is particularly important that the active agent should not be applied to the normal skin and therefore a paste is used for the abnormal areas. Pastes can also be used to protect inflamed or excoriated skin and can be applied very freely. A good example is compound zinc paste.
Lotions
Water lotions are used to cool acutely inflamed skin and may have to be frequently reapplied. Potassium permanganate lotion is very helpful for acute exuding lesions of the hands and feet. Lotions should generally not be used when the acute phase has subsided.
Lotions cool by evaporation and leave an inert powder on the skin surface. They are useful and safe for subacute lesions. Calamine lotion is a good example.
Dusting powders
These are drying agents and increase the effective evaporating surface. They are particularly useful in the folds of the skin. Talc, starch and zinc oxide are commonly used powders. Active agents can be added as needed – for example, antiseptics for bacterial infections and antifungal agents for athlete’s foot (tinea pedis).
Ingredients in preparations
The base
When formulating a skin preparation, the first decision to make is the type of base that will be used. This will depend on the acuteness of the lesion. Many lesions in fact often derive more benefit from the base than from the active agent. A decision on the active ingredient to be added generally implies a diagnosis of the skin disorder. It is no longer useful to remember detailed prescriptions because the common ones can be found in the British National Formulary (BNF) or equivalent publications. Ointments prepared by pharmaceutical companies have complicated formulae, but it is very important to know the active ingredients and their strength in these preparations.
It is also important to check for additives in topical preparations, which may be associated with sensitization (Table 29.1).
| Ointments and creams | Sensitizer |
|---|---|
| Beeswax | Isopropyl palmitate |
| Benzyl alcohol | Polysorbates |
| Butylated hydroxyanisole | Propylene glycol |
| Chlorocresol | Sorbic acid |
Active ingredients
Local corticosteroids
These are probably the most widely prescribed and useful ingredients to be added to the various bases. For this reason they are often overprescribed and in particular they should not be used alone where the cause of the skin disease is a bacterial, fungal or viral infection as they may cause spread of the infection by lowering local resistance. They are very useful for acute and subacute disorders such as the eczemas and they are excellent for itching (pruritus).
Topical corticosteroids are classified according to their potency (Table 29.2).
| Potency | Examples |
|---|---|
| Mild | Hydrocortisone 1% |
| Moderately potent | Clobetasone butyrate 0.05% |
| Potent | Betamethasone valerate 0.1%, mometasone furoate 0.1% |
| Very potent | Clobetasol propionate 0.05% |
The choice of a topical corticosteroid should be the least potent preparation at the lowest strength which is effective.
Hydrocortisone ointment (0.5–1%) is the most useful, standard preparation. Nothing stronger than this should ever be used in infants or on the face. (In certain cases, a short course of a more potent preparation may be prescribed under strict supervision of the dermatologist.) These ointments need not be applied more than twice a day.
More potent corticosteroids (e.g. betamethasone valerate) can achieve a much more intense effect than hydrocortisone, but this may not be an advantage and can lead to atrophy of the skin. They are valuable for thick, dry skin disorders, such as the chronic eczemas, or with some special disorders such as lupus erythematosus. The absorption of these preparations is enhanced by occlusive dressings – for example, if they are covered with polythene. However, there is great danger of secondary infection with this method.
It has been suggested that corticosteroids should be used not more than once daily in atopic eczema (see Charman 2000).
Sometimes corticosteroids are combined with an antibacterial or antifungal agent and used to treat dermatoses with superimposed bacterial or fungal infections.
Coal tar
Coal tar applied to the skin is an antimitotic and anti-inflammatory agent. A tar is the product of the destructive distillation of organic substances, and coal tar is in many valuable preparations, although their use has been superseded by the corticosteroid preparations. For disorders such as psoriasis and chronic eczema they are preferred because there are fewer side-effects. Cosmetically acceptable preparations are now available and a liquid form can be added to the bath for the treatment of some patients with psoriasis. The BNF calamine and coal tar ointment contains the equivalent of 0.5–1.0% of tar. Coal tar pastes are also often used in eczemas. A useful preparation for psoriasis is betamethasone valerate ointment with liquor picis carb (tar) in yellow soft paraffin.
Dithranol is widely used to treat psoriasis (Case History 29.1). It is an irritant and application must be limited to the psoriatic areas as it burns normal skin, particularly if the skin is fair or has previously been treated with steroids. It should not be used if there is evidence of infection.
Clinical note
Clinical note
Psoriatic arthritis has been found to respond dramatically to treatment with the newer drug infliximab, a drug given systemically by intravenous infusion to treat rheumatoid arthritis (see p. 156).
CASE HISTORY 29.1
..
Several months after his retirement Mr T developed such an itchy skin that he was unable to avoid persistent scratching. He went to the doctor, who observed that Mr T had generalized dryness and scaling and complained of pruritus. He was referred to the dermatologist, who examined his skin. Eczema, psoriasis, contact dermatitis and any infestation were excluded as causes of the pruritus. Blood tests and a skin biopsy were arranged to exclude any other possible cause of the itching, such as iron deficiency, renal, liver or thyroid disease, or a malignancy. Mr T’s diagnosis was pruritus of the elderly (senile pruritus) and he was prescribed Eumovate (clobetasone), a topical corticosteroid ointment, for 5 days to relieve the acute itching, as well as regular emollient therapy. He was referred to the nurse specialist, who showed him how to apply the ointment and a range of samples of different emollients to discover which would be the most suitable for him and which he would prefer to use. Mr T then commenced an emollient regimen that included aqueous cream as a soap substitute and an emollient containing an antipruritic ( Balneum Plus) to use in his bath. He was advised to use a non-slip mat in the bath. As a regular moisturizer, a fragrance-free, hydrating gel containing liquid paraffin ( Doublebase) was prescribed for him, to be applied after the bath and frequently during the day. Follow-up appointments were made with the nurse specialist to monitor progress and in case of an underlying lymphoma or systemic disease.
Antibacterial agents
If a bacterial infection is suspected, it is important to send a swab to the laboratory for culture and sensitivity tests first. In addition, many infections of the skin are best treated with systemic rather than topical antibacterial agents. The prolonged use of most antibacterial agents (e.g. neomycin) on the skin carries a very high risk of sensitization to the agent, so that a bacterial infection may be replaced by a contact dermatitis! Chlortetracycline is probably the best to add to an ointment. If topical antibacterial agents are used, the treatment should be determined by the sensitivity of the organism. Sulphonamides and penicillin should never be used on the skin owing to the high risk of sensitization.
Antifungal agents
Skin scrapings to identify the fungus are best taken before commencing treatment. Systemic treatment is used for widespread, unresponding fungal infections and for nail (tinea unguium) and scalp ringworm. Griseofulvin is the drug of choice for widespread or intractable fungal infections of the skin. It is more effective in the skin than in the nails and needs to be continued for some months.
Topical treatments are usually adequate for most localized infections.
An acute fungal infection used to be treated with potassium permanganate lotion 0.01% for the first few days, but this is now rarely used for this purpose. An ointment with salicyclic acid and benzoic acid is known as Whitfield’s ointment and is still used, but tends to be cosmetically unacceptable. Effective preparations which are commonly used are the imidazoles clotrimazole, econazole and miconazole. The undecenoates and tolnaftate are less effective in the treatment of ringworm infections. Terbinafine is now also available in the form of a cream. Amorolfine is an antifungal which is available as a cream for fungal skin infections and as a lacquer for fungal nail infections.
Lotions and creams are usually the vehicle of choice. As ointments have occlusive properties they should be avoided on moist areas. Dusting powders are therapeutically ineffective in the treatment of fungal infections and liable to cause skin irritation, and should be avoided except for toiletry purposes.
Infections with Candida albicans are common in patients with diabetes mellitus and those who have been treated with antibiotics and immunosuppressive drugs. Treatment may be with the broad-spectrum antifungal imidazoles. Nystatin is also equally effective and must be applied to the affected area, either as an ointment or a lotion.
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