VOL: 98, ISSUE: 09, PAGE NO: 55
Molly Courtenay, PhD, MSc, CertEd, RNT, RGN, is senior lecturer, Buckinghamshire Chiltern University College, Chalfont St Giles;Michele Butler, MMedSci, BSc, RGN, RNT, Cert.Ed (FE), is senior lecturer in clinical science, School of Biological and Molecular Science, Oxford Brookes University
The skin is the largest of the body’s organs. Its surface area spans approximately two square metres and accounts for roughly 16% of an individual’s total body weight.
The skin is composed of two major layers of tissue; the outer epidermis, and the inner dermis (Fig 1). It also has a number of accessory structures including hair, nails, sweat glands, and sebaceous glands. These structures, although located in the dermis, protrude through the epidermis to the skin surface.
The skin has a number of functions. These include:
- Protection of underlying organs and tissues;
- Excretion of waste products, salts and water;
- Maintenance of normal body temperature;
- Storage of nutrients;
- Detection of stimuli, such as temperature, and the relay of this information to the nervous system (Martini, 2000).
The skin is persistently subjected to mechanical injury. The epidermis provides protection, and also prevents micro-organisms from entering the body. It is comprised of a number of layers. The innermost layer of the epidermis is called the stratum germinativum, and the outermost layer the stratum corneum. The stratum germinativum is attached to a basement membrane which separates the dermis from the epidermis.
The stratum germinativum is composed of many germinative or basal cells, the division of which replace the cells shed at the epithelial surface. As these germinative cells move towards the skins surface their structure and activity changes. While still at the basal layer they begin forming a protein called keratin. The formation of this protein is continued as they move towards the skin’s surface. Eventually, as the cells reach the stratum corneum approximately 15-30 days later, they are like flattened bags of protein and their intracellular organelles have disappeared.
Before they are lost from the stratum corneum, these cells remain in this layer for a further two weeks. This provides the underlying tissue with a protective barrier of cells which, although dead, are exceedingly durable.
The stratum corneum is the major barrier to the loss of water from the body. It has two actions which restrain the movement of water and limit the loss of water from the skin’s surface. First, the matrix in which the cells of the stratum corneum are embedded is rich in lipid. This substance is almost impenetrable to water and therefore makes it extremely difficult for water molecules to move out of the epidermal cell. Secondly, protein inside the epidermal cells attracts and holds on to water molecules. As a consequence of these actions, the surface of the skin is therefore normally dry, with very little water lost and so is, therefore, unsuitable for the growth of many micro-organisms. Although water-resistant, the stratum corneum is not waterproof. Interstitial fluid gradually penetrates this layer of tissue to be evaporated from the surface into the surrounding air. Approximately 500ml is lost from the body each day in this way.
The dermis is comprised of a network of two types of protein - collagen and elastin. The collagen fibres provide strength to the skin. The elastin gives the skin its flexibility. The dermis is also comprised of a network of blood vessels and a number of other structures. These include sweat glands, which are found all over the skin and secrete a dilute salt solution on to the skin’s surface; sebaceous glands, found everywhere in the body except non-hairy areas, which secrete sebum containing a mixture of lipids; sensory receptors and defence cells.
There are variations in the structure of the skin in relation to age, environment, and ethnic origin. The skin also varies between different parts of the body.
Candidiasis of the skin
Candida albicans is a yeast-like, opportunistic fungus that is responsible for candida infection of the skin. It is part of the normal flora of the mouth, intestine and vagina of humans. However, it is responsible for infection in these sites when local conditions are disrupted or defence mechanisms become impaired. Areas affected are mainly the mucosae, where C. albicans is normally present in health, and on regions of moist skin. The infection is more commonly referred to as ‘thrush’.
Clients most susceptible to opportunistic C. albicans include:
- Pregnant women;
- Debilitated infants;
- Elderly people;
- Those with immunodeficiency (for instance, clients with AIDS, clients receiving cancer chemotherapy);
- Those having received antibiotic or corticosteroid therapy;
- Those with indwelling urinary or intravenous catheters;
- Those with diabetes mellitus (Brooks et al, 1991).
Preparations used for the treatment of candida infections of the skin
Preparations listed in the extended NPF allow nurse prescribers to treat oral candida and candida infection of the skin and genital region. POMs in the extended formulary for candida infections of the skin include the following:
- Clotrimazole 1% and betamethasone 0.05% as dipropionate cream (Lotriderm);
- Clotrimazole 1% and hydrocortisone 1% cream (Canesten HC);
- Econazole 1% and hydrocortisone 1% cream (Econacort);
- Ketoconazole 2% cream (Nizoral);
- Miconazole nitrate 2% and hydrocortisone 1% cream and ointment (Daktacort);
- Nystatin cream 100,000units/g, hydrocortisone 0.5%, and chlorhexidine hydrochloride 1%, ointment nystatin 100,000 units/g, hydrocortisone 05% and chlorhexidine acetate 1% (Nystaform-HC);
- Nystatin 100,000 units/g cream and ointment (Nystan);
- Sulconazole nitrate 1% cream (Exelderm)
- Hydrocortisone 0.5%, nystatin 100 000/g, benzalkonium chloride solution 0.2%, dimeticone ‘350’ 10% cream (Timodine).
Mode of action
Clotrimazole, econazole, ketoconazole, miconazole and sulconazole are all imidazoles - broad-spectrum drugs that act by inhibiting ergosterol synthesis in the fungal cell membrane. Ergosterol is a major constituent of the fungal cell membrane, and thus fungal growth is prevented. Nystatin, however, binds to ergosterol and alters membrane permeability and allows leakage of intracellular contents.
These preparations are applied topically in candidiasis skin infections. Systemic adverse effects are rare as drug absorption is only slight. However, they can include a diuretic effect, abdominal cramping and local irritation (Galbraith et al, 1999).
Some of these products have been combined with a corticosteroid (hydrocortisone or betamethasone) to help alleviate the inflammation that might accompany a fungal infection. Mild and moderately potent topical corticosteroids are rarely associated with side-effects. However, care must be taken if products are applied over a large surface, if an occlusive dressing is applied to the area or if the skin is damaged, as systemic absorption will be increased. Permanent changes to the skin will occur if potent corticosteroids are used in high concentrations over a prolonged period of time. Thinning of the skin and prominent blood vessels are the most common side-effects. Therefore, if they are to be applied to the skin on the face, only mild corticosteroids should be prescribed. Rebound erythroderma can occur if a treatment is stopped abruptly (Henry, 2000).
Lotriderm is a potent topical corticosteroid. Therefore care is required, as absorption through the skin can cause serious side-effects. The remaining preparations are mild and so side-effects are minimal.
Bacterial or fungal infections of the skin are never treated solely with corticosteroids, as they suppress the activity of the immune system and increase the risk of infection.
Topical antifungal treatment is usually all that is necessary to treat skin candidiasis. If there is inflammation, an antifungal preparation combined with a corticosteroid may be of value. Soap and water should be used to clean the skin before applying the product to the affected areas. The preparation should be applied according to product licence, evenly but not too thickly, using soft, gentle strokes to ensure absorption (carers or nurses should wear gloves). Medical advice should be sought if the skin infection is extensive or the client is immunocompromised.
Acne occurs in both males and females at about the time of puberty. It is a disease of the sebaceous glands (Galbraith et al, 1999). If too much sebum is produced, its flow becomes blocked by debris produced by the skin or sebum which has become hardened. This leads to an accumulation of sebum and acne.
Mild acne presents with blackheads and an occasional pustule. Moderate acne involves large numbers of pustules and papules and in severe acne the skin becomes inflamed and cysts can be found in the inflamed dermis.
A number of products are used to treat acne. These include keratolytics, antimicrobials or retinoids. Preparations include:
- Adapalene 0.1% cream and gel (Differin);
- Azelaic acid 20% cream (Skinoren);
- Benzoyl peroxide 5% and erythromycin 3% in an alcoholic basis (Benzamycin);
- Clindamycin phosphate lotion 1% in aqueous basis (Dalacin T);
- Clindamycin phosphate topical solution 1% in aqueous alcoholic basis (Dalacin T);
- Erythromycin 2% and 4% in alcoholic gel basis (Eryacne2, Eryacne4);
- Erythromycin 2% solution in alcoholic basis (Stiemycin);
- Isotretinoin gel 0.05% (Isotrex);
- Isotretinoin 0.05% and erythromycin 2% in ethanolic gel (Isotrexin);
- Tetracycline hydrochloride 2.2mg/ml solution (Topicycline);
- Tretinoin 0.025% cream, 0.01% and 0.025% gel, 0.025% lotion (Retin-A);
- Erythromycin 40mg and zinc acetate 12mg/ml in ethanol solvent (Zineryt);
Benzoyl peroxide: mode of action
Benzoyl peroxide unblocks sebaceous follicles by removing the top layer of skin. Inflammation of the blocked follicle is reduced as this preparation also kills the bacteria causing the infection.
Benzoyl peroxide should not be allowed to come into contact with the mouth, mucous membranes or eyes. It may cause skin irritation.
Antibiotics: mode of action
There are five major mechanisms by which antibacterial drugs have their effect. These are:
- Inhibition of synthesis and damage to the bacterial cell wall;
- Inhibition of synthesis and damage to the bacterial cell membrane;
- Modification of bacterial nucleic acid synthesis;
- Inhibition or modification of bacterial protein synthesis;
- Modification of bacterial energy metabolism.
- Tetracycline, erythromycin and clindamycin inhibit or modify bacterial protein synthesis (Wingard et al, 1991).
They each act by binding to one of the subunits of the bacterial ribosomes where proteins are actually manufactured, and hence prevent protein synthesis.
Fusidic acid prevents transfer ribonucleic acid binding to the ribosomes. Protein synthesis inhibitors tend to have bacteriostatic properties.
Topical preparations can produce irritation of the skin and, in rare cases, an allergic reaction (Henry, 2001.
Azelaic acid 20% cream (Skinoren)
This cream has a bacteriostatic action and is used in mild to moderate acne. It should be applied once or twice a day. Application for up to six months may be required.
Retinoids: mode of action
Systemic retinoids appear to reduce sebum production and enable the drainage of sebum by causing the epidermal layer to be less cohesive (Hopkins, 1999).
Retinoids should not be applied during pregnancy or if breast-feeding. Tretinoin is contraindicated if the client has a history of cutaneous epithelioma. These preparations should not be applied when acne covers a large area or the skin is broken. Exposure to ultra-violet light and astringents should be avoided.
The side-effects of these preparations include local irritation, dry skin and an increased sensitivity to sunlight. During the initial stages of treatment with tretinoin acne can become exacerbated.
In mild cases of acne, regular washing and moderate exposure to sunlight or ultraviolet light is normally all that is required. Topical preparations are generally used to treat mild to moderate acne. In more severe cases, oral antibiotics might be required. These include oxytetracycline, doxycycline, tetracycline and minocycline.
** This article is based on a book by Courtenay, M. and Butler, M. Essential Nurse Prescribing, to be published in April 2002 by Greenwich Medical Media, London