Dr Heidi Schroeder BVSc MMedVet(Med)
Willow Park Small Animal Medicine Specialist Hospital
The use of therapeutic shampoos for the treatment of skin diseases has become an integral part of the treatment regimes of Veterinary Dermatology. Veterinarians should know details about the composition of shampoos, their mechanism of action, and when and how to use them. This will help in instructing owners and obtaining the best treatment results.
A shampoo is an aqueous solution, with added surfactants, cleansing agents and various therapeutic and/or cosmetic agents. In animals, the hair coat penetrating and cleansing effect of a shampoo has a great advantage over the use of other topical formulations such as creams and ointments. The pH of a dog’s skin is different from that of a human. The pH of canine skin is 7.5 compared to 5.5 for human skin. Due to the alkalinity of a dog’s skin, it provides a favourable environment for bacterial growth. Many skin diseases in small animals have a wide spread to generalised distribution. Shampoos are particularly useful for the treatment or management of such disorders.
Medicated shampoos work in more than one way. They allow application of specific therapeutic molecules to skin and hair, restore normal structure and function of the skin and cleanse the skin and hair of microbes and parasites, allergens and other harmful material. In this way they enable many specific and non-specific dermatological disorders to be effectively treated, managed or prevented.
The therapeutic molecules need to be absorbed and to penetrate to the deeper layers of the skin in high enough concentrations in order to achieve a therapeutic effect. The time needed to achieve this, is known as the contact time. Contact time can be defined as the time interval between the end of applying the shampoo and rinsing it off. Contact time is usually between 5 and 15 minutes. In most shampoos the active ingredients are removed when the shampoo is rinsed off. To be fully effective many medicated shampoos have to be repeated very frequently. This may lead to dehydration of the stratum corneum and loss of the protective barrier function and often leads to disappointing results. The correct contact time and correct frequency of the shampoo therapy are therefore crucial for success.
Shampoo therapy for specific dermatological disorders
There are 6 categories of dermatological disorders which will be discussed with special focus on shampoo treatment of these disorders:
- Keratoseborrhoeic disorders (KSD)
Keratoseborrheic disorders (KSDs) are those that alter the surface appearance of the skin. The epidermis of animals is constantly being replaced by new cells. The normal epidermal cell renewal time is approximately 22 days. Despite this high turnover rate, the epidermis maintains its normal thickness, has a barely perceptible surface keratin layer, and loses its dead cells invisibly to the environment. If the delicate balance between cell death and renewal is altered, the epidermal thickness changes, the stratum corneum become noticeable, and the normally invisible sloughed cells of the stratum corneum become obvious.
Keratoseborrheic disorders (KSD) are characterized by scaling, crusting, greasy or dry skin and alopecia and can be primary or secondary. Generally the primary KSDs are hereditary and are associated with a primary keratinisation defect. They usually manifest clinically by excess scale formation in which the primary pathophysiology involves a defect in the keratinising epithelium or cutaneous glandular function. Clinical signs will usually appear during the first 2 years of life. Primary KSDs include primary idiopathic seborrhoea, epidermal dysplasia, Schnauzer comedo syndrome, canine ichthyosis and canine acne. These cases usually cannot be cured and very often need life long or long term treatment. Breeding with affected individuals should be discouraged.
At least 80% of KSD cases seen in general practice are secondary. The most common causes include allergies (flea allergic dermatitis, atopic dermatitis and cutaneous adverse food reactions), bacterial infections, immune-mediated disorders, endocrine disorders, parasitic disorders (scabies, demodicosis, and cheyletiellosis), fungal infections and nutritional disorders.
Shampoos containing keratomodulating and/or antiseborrheic agents, as well as essential fatty acids, are indicated for these disorders.
Keratomodulating agents have two mechanisms of action.
- Firstly they restore normal keratinocyte multiplication and keratinisation by exerting a cytostatic effect on the basal cells, thereby reducing their rate of division. Agents working in this way are called keratoplastic (keratoregulating).
- The second mechanism of action is the elimination of excess keratin of the stratum corneum, either by increasing desquamation, by reducing intercellular cohesion or by breaking up keratin. Agents working in this way are called keratolytic. Keratolytic agents therefore break down the keratin layer.
There are several types of keratomodulating agents, e.g. salicylic acid and sulphur.
- Salicylic acid (0.5 – 2%) is keratolytic. It causes a reduction in skin pH, which leads to increased hydration of keratin. These actions help to soften the corneal layer. It has direct effects on the intercellular junction system (desmosomes) with solubilisation of intercellular cement and facilitation of keratinocyte detachment (desquamation). It acts synergistically with sulphur and is often present in small quantities in shampoos, its efficacy varying with concentration.
- Sulphur (0.5 – 2 %) is mildly keratolytic (forms hydrogen sulphide in the stratum corneum), keratoplastic (has a direct cytostatic effect, interacts with epidermal cysteine to form cystine which is an important component of the stratum corneum), and has numerous antiseborrheic effects. It is gradually being replaced in topical products by more effective keratomodulating agents with fewer side effects (e.g. a rebound increase in scaling). It is not a good degreasing agent. Sulphur may be used in cats.
Antiseborrheic agents inhibit or reduce sebum production by the sebaceous glands, and help clear the ducts. These agents act at the level of the sebaceous gland and its duct. Examples are sulphur and benzoyl peroxide.
- Sulphur is a classic antiseborrheic agent, but is drying and may trigger a rebound effect. It exerts a synergistic activity with salicylic acid. This synergism appears optimal when both substances are incorporated into the shampoo in equal concentrations.
- Benzoyl peroxide is antiseborrheic by causing sebum hydrolysis and reduced sebaceous gland activity. It exerts a follicular flushing action which is useful when treating disorders associated with come domes and/or follicular hyperkeratosis. It is bactericidal and keratolytic. It is particularly useful in severe cases of greasy seborrhoea with or without pyoderma. Side effects such as irritations and erythematous rashes have been reported especially in concentrations higher than 5%. Long term use may lead to a dry skin. Emollients are always indicated after treatment with this agent.
Essential fatty acids
Essential fatty acids have been incorporated in to various veterinary shampoos for their softening and moisturizing properties. These include linoleic acid, glycerine, lactic acid, ceramides and fatty acid polyesters.
Principles of shampoo therapy for KSDs
- Mild, dry scaling often responds to a moisturising, hypoallergenic shampoo.
- More severe dry scaling responds to sulphur, salicylic acid combinations, preferably combined with moisturisers.
- Greasy, oily scaling requires benzoyl peroxide.
Guidelines for the use of shampoo therapy in KSDs
- Long haired dogs with severe seborrheic disorders should be clipped as this leads to more effective application and better distribution of the active ingredient;
- Shampoos should initially be used 2 to 3 times weekly. With time, frequency of application can gradually be reduced;
- Cases should be monitored frequently. The therapeutic agent often needs to be changed following the development of side effects or change in clinical presentation (e.g. transition from greasy to dry seborrhoea).
- Bacterial skin infections (Pyoderma)
Bacterial pyodermas are pyogenic infections of the skin and occur due to the multiplication of bacteria on or in the epidermis and its appendages and with invasion of the dermis. Pyodermas are almost always secondary. Classification of pyoderma based on depth of bacterial involvement is clinically the most useful, because it provides information on diagnosis, differential diagnosis, underlying disease, prognosis and response to treatment. Pyoderma may be on the skin surface, affecting the stratum corneum and outer epidermis (e.g. intertrigo and pyotraumatic dermatitis); superficial, involving only the epidermis (e.g. impetigo) and the epithelial appendages in the dermis (e.g. folliculitis) or deeper, compromising structures in the dermis and deep, subjacent fatty tissue.
The development of pyoderma occurs in 2 stages. Firstly the microbes colonise areas of the body surface. This occurs commonly as many skin diseases are aggravated by microbial colonisation or invasion. The second phase occurs when the stratum corneum is invaded to cause impetigo and/or invasion of the hair follicles causing folliculitis. The latter two are classified as superficial pyoderma. When the infected hair follicle ruptures, the infection spreads into the dermis (furunculosis) or spreads more deeply along tissue planes (cellulitis). The latter 2 are termed deep pyodermas. Resolution depends on the non-specific defenses (neutrophils and macrophages) and on the specific defenses (cell mediated immunity and antibodies). Resolution is accompanied by an inflammatory response, which is responsible for the clinical signs of pyoderma.
Shampoos are used to decrease the number of microbes on the skin surface and rinse them off. This interrupts the microbial colonisation, thus sustaining the restoration of normal skin structure and function. Shampoos are also used in pyoderma cases to remove tissue debris, to allow direct contact between the active ingredient and the organism, encourage drainage and decrease pain and pruritus.
Chlorhexidine is a synthetic biguanide, an antiseptic that is very effective against most bacteria (gram + and -), fungi and Malassezia pachydermatis. This molecule exists as various forms of salts. Chlorhexidine digluconate is the most used form in topical dermatology. It is bactericidal by action on the cytoplasmic membrane, which causes leaking of intracellular components. It is characterised by a rapid “kill” action, has a 36-hour residual activity and is non-toxic and non-irritant.
Povidone-iodine is an iodophore which slowly releases iodine to tissue. The titre able iodine is usually of the order of 0.2 to 0, and 4 %. It is an effective broad-spectrum antimicrobial and is useful for local lesions. It has a prophylactic effect because of its persistence on the skin. It is not advisable to be used repeatedly for generalized skin problems due to its irritant and staining properties.
Benzoyl peroxide is metabolised in the skin to benzoic acid and much of its microbicidal activity probably derives from the lowered skin pH. This disrupts microbial cell membranes. It is also an oxidizing agent, which releases nascent oxygen into the skin and produces a series of chemical reactions resulting in permeability changes and rupture of bacterial membranes. It has an excellent prophylactic effect. It is generally used in concentrations of 2 to 3%, which are well tolerated, but irritation can occur at higher concentrations (erythema, pruritus and pain). Benzoyl peroxide is toxic to cats. It may, however, be used sparingly/diluted on local lesions such as chin acne or stud tail.
Piroctone olamine is an antiseptic agents that has broad in vitro activity against major dermal veterinary pathogens, including dermatophytes and yeasts as well as gram positive (Staphylococcus) and gram negative (Pseudomonas) bacteria. Piroctone olamine is unrelated to other antiseptics used in Veterinary Medicine. Members of the “pirox” family are used in the human field to cure onychomycosis and Malassezia related skin disorders. No resistance has been documented to date. In addition, this antiseptic acts at low concentrations, has high affinity for keratin and is completely safe.
Quaternary ammonium compounds are surface acting agents. They have less effect and are only useful for limited bacterial involvement.
Guidelines for the use of shampoo therapy in bacterial pyodermas
- In general, most patients with bacterial pyoderma will be treated with systemic antibiotics, and topical therapy is used as an adjunct treatment. The exceptions would be those dogs that have surface or superficial pyoderma.
- It is important to pre-bath with a mild cleansing shampoo to remove grease, debris and dirt prior to using the medicated shampoo.
- Cases of deep pyoderma need to be clipped before using shampoos. This prevents the formation of sealing crusts and allows the active ingredients to come in contact with the lesions.
- The frequency of bathing will depend on the individual patient, but in general for active infections medicated baths should be administered 2-3 times weekly.
- A common indication for the long term use of shampoos is in the dog suffering from recurrent folliculitis (idiopathic of secondary to endocrine or allergic skin disease). Here antibacterial shampoos may have a prophylactic effect if used regularly e.g. weekly or every two weeks.
- Fungal skin infections
Malassezia dermatitis is a fungal skin infection. The pathogenic agent, Malassezia pachydermatis, is a lipophilic yeast belonging to the cutaneous microflora of the normal dog, along with Staphylococcus pseudintermedius. In certain conditions, related to cutaneous and/or immune-mediated factors, Malassezia may proliferate within the stratum corneum. The subsequent yeast overgrowth may then acquire a real pathogenic capacity and initiate a true dermatitis. It is recognised as a secondary pathogen in a large number of skin conditions, e.g. in dermatoses associated with dry or greasy scales, inflammatory and pruritic skin conditions and in various pyodermas. It may also be a primary pathogen.
Topical therapy is often used for the treatment of Malassezia infections and may also be beneficial when used routinely to help prevent recurrence of infection. Shampoo therapy is most useful for generalized infections, while localized infections may benefit from creams, lotions and sprays. Dogs with severe generalised Malassezia infections show the most rapid response where shampoo therapy is used in conjunction with systemic therapy (as compared to topical therapy or systemic therapy alone).
Active ingredients in topical preparations that may be useful in managing Malassezia infections include: imidazoles (miconazole, ketoconazole, enilconazole), chlorhexidine, and piroctone olamine.
Imidazoles act by interfering with cell wall formation in fungal and yeast organisms, which increases cellular permeability, thus suppressing metabolic function and inhibiting growth. There has also been evidence that ketoconazole exerts an inhibitory effect on keratinocytes in culture. In a study by Jasmin and co-workers a 3% chlorhexidine shampoo was highly effective in the treatment of Malassezia dermatitis and also aided in the treatment of the concurrent bacterial pyoderma when present. The product had similar efficacy whether dogs were affected with concurrent pyoderma (treated with systemic antibiotic) or not, and whether an underlying dermatosis was present or not.
The use of a keratoseborrheic shampoo prior to applying the antifungal shampoo enhances the effectiveness of the antifungal agent.
Dermatophytosis is a fungal infection of the keratinised tissues, i.e. the hair, stratum corneum, nails and claws. It is caused by Microsporum spp. (70% of cases) and Trichophyton spp. (30% of cases) in dogs. Microsporum canis causes 98% of all cases in cats.
The best treatment protocol is a combination of topical treatment (to kill infective material and prevent its dissemination into the environment and to accelerate recovery), systemic treatment (to shorten the time of infection in the infected animal) and environmental treatment (to help prevent recurrence of infection or spread to other animals or people in the household).
Topical treatment may include the following: imidazoles (miconazole, ketoconazole, enilconazole), lime sulphur, chlorhexidine and piroctone olamine.
In a study by White-Weithers and Medlieu, seven commonly used, topical antifungal products (i.e., lime sulfur, chlorhexidine, captan, povidone-iodine, sodium hypochlorite, and enilconazole solutions, and ketoconazole shampoo) were evaluated for their antifungal activity on Microsporum canis-infected hairs from dogs and cats in an in vitro study. Hairs were soaked or shampooed in each product for five minutes twice a week for four weeks. Of the seven products used in this study, lime sulfur and enilconazole solutions were superior in inhibiting fungal growth; no growth occurred on fungal cultures after two treatments with either product. Chlorhexidine and povidone iodine solutions were effective after four treatments, and sodium hypochlorite solution and ketoconazole shampoo inhibited fungal growth after eight treatments. Captan did not inhibit fungal growth during the test period.
Guidelines for the use of topical therapy in dermatophytosis
- · Clipping the hair coat is recommended in generalised infections to decrease shedding of contaminated hairs into the environment.
- · Owners should be warned that animals may have more lesions during the first week after clipping.
- · Keratomodulating shampoos can be used before antifungal therapy when indicated as they are beneficial in removing infected scales and crusts.
- Allergic skin diseases
Shampoo therapy often contributes a large part in the management of allergic skin diseases. Shampoos rehydrate the skin and result in the patient looking, smelling and feeling better. Shampoos therapy in cases with allergic skin disease helps to eliminate allergens from the skin surface, helps to restore the epidermal barrier and helps to control the inflammatory process and secondary skin infections.
There are a variety of shampoos available that may be used in the management of an allergic skin disease:
Shampoos with an antipruritic effect can improve the condition of allergic dogs, especially when they are used frequently (e.g. twice a week, at least initially). The most widely recommended topical antipruritic agent is colloidal oatmeal. It has both emollient (softens, lubricates, soothes) and hydroscopic (incorporated into the stratum corneum and attracts water) activities and has a direct anti-inflammatory and antipruritic action. The exact mechanism is not clear.
Antibacterial and antifungal shampoos e.g. chlorhexidine may be used to control secondary bacterial and /or yeast infections.
Keratomodulating shampoos are indicated in cases with allergy induced keratoseborrheic changes.
Cleansing, non-irritating shampoos, fatty acid shampoos and ceramide containing shampoos may be used to improve or restore the epidermal barrier.
A shampoo specifically designed for canine atopic dermatitis has been recently developed (AllermylÒ). It was designed to restore cutaneous integrity and maintain the epidermal barrier function, control aggravating microbial proliferation, and to limit immune and inflammatory reactions. It contains linoleic acid, gamma-linolenic acid, mono and oligosaccharides, vitamin E, and piroctone olamine.
- Parasitic skin disorders
Antiparasitic shampoos, e.g. containing organochlorins, natural pyrethrins or synthetic pyrethrins, are not considered to be as efficacious as antiparasitic rinses and dips and other formulations (sprays, spot-ons), mainly because they are rinsed and cannot act during a sufficient time. Their main use is for quick removal of fleas in puppies, kittens and debilitated animals.
Colloidal oatmeal can be used to decrease inflammation and pruritus due to parasitic infestation.
Benzoyl peroxide shampoos are recommended in the treatment of demodicosis because of their degreasing and follicular flushing effect.
Many parasitic diseases such as scabies, cheyletiellosis and flea allergic dermatitis can cause a keratoseborrheic disorder and affected animals will benefit from application of keratomodulating shampoos.
- Dry sensitive skin
Dry skin results from increased water loss through the skin. It occurs in many skin conditions, such as allergies, with excessive use of corticosteroids or due to treatment with inappropriate shampoos.
Water by itself has a strong hydrating effect if used properly. A contact time of 10 – 15 minutes should be allowed to properly hydrate the stratum corneum. If the contact time is too short or baths are given too frequently, the skin will dry further by evaporation of water.
Emollients are used to cover the surface of the skin, thus decreasing transepidermal water loss and keeping the skin soft and pliable. They are usually based on plant or mineral oils. Today emollients are rarely used in veterinary medicine, except for topically applied essential fatty acids. They reduce transepidermal water loss by being incorporated into the stratum corneum ceramides.
Humectants are oil free agents that work by being incorporated in the stratum corneum and attracting humidity from the lower layers of the epidermis. They are colloidal oatmeal, sodium lactate, urea, lactic acid, propylene glycol, glycerine or carboxylic acid. Humectants are used to rehydrate dry skin and may be applied in between baths.
This category includes products said to be “hypoallergenic” and “All-natural.” Some of these shampoos, however, contain colorants, whiteners, deodorants, added colours or fragrances that can be potent irritants and sensitisers for allergies. True hypoallergenic shampoos should contain few substances that could cause an allergic reaction. They should be the least irritating shampoos on the market. “All-natural,” which means that none of its components are manmade or synthesized, should not be confused with “hypoallergenic.” Some natural ingredients, including oatmeal, aloe vera, melaleuca oil, tea tree oil, citrus extracts and eucalyptus, may be primary irritants or allergens. Others, such as eucalyptus, used for their moisturizing and/or anti-inflammatory properties, can be potent allergens.
Successful treatment is rarely based on shampoos alone. Therapeutic shampoos are often used as an adjunct to systemic, usually oral therapy, e.g. antibiotics and antifungals. They help to achieve better and faster results and prevent early recurrence by restoring normal structures and functions of the skin. Shampoos cause the patient to feel better and smell better and that is already very encouraging for the owners. Advantages include direct therapeutic access to target organ, reduction in systemic absorption and adverse effects and better delivery systems of the new generation shampoos. Shampoo therapy must be carefully adjusted to the needs of the individual. Good communication with the client and evaluation of their compliance is crucial for successful treatment. The contact time and the correct frequency of the shampooing are crucial. Shampoo therapy increases the cost of therapeutic plan, but appropriate topical therapy may greatly reduce the need for systemic treatment.
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