Drugs used in dermatological conditions

The skin the skin is the largest organ, 4 kg & 2m2 important functions as, defense, physical barrier, heat regulation, sensation, vitamin D synthesis Composed of 3 layers, epidermis, dermis & subcutaneous fatty tissue Both topical & systemic medications can be used depending on nature & extent of disease

Topical preparations Convenient & minimize systemic side effects Formulated as cream, ointment, lotion, spray, gel, paste, powder, & packed dressings Bioavailability depends on the vehicle (oil or water) & method used to localize it. Efficacy depends on: thickness of skin, concentration, frequency of application, age & health of skin Generally lipophilic more readily absorbed than hydrophilic

Drugs used in acne Pathogenesis of acne Retinoids: vitamin A derivatives, used in acne, psoriasis & photoaging The first generation: topical Tretinoin (Retin A), & systemic Isotretinoin (Roaccutane) only in severe cystic acne The 3rd generation as adapalene & tazarotene, more effective & less irritating, in comedonal & inflammatory acne.

mechanism of action Acts on proliferation & differentiation of keratinocytes Immune function Anti inflammatory action In first generation reduction of sebum production Their action is on the nucleus by binding to a specific receptor & acts as a transcription factor thereby influencing cell differentiation & proliferation Side effects of topical: dryness, irritation, peeling Systemic: Teratogenic, depression & suicide, dryness of skin & mucosa

Other agents for acne Benzoyl peroxide: antiseptic & comedolytic, in mild to moderate non inflammatory acne, also irritant, many over the counter preparations Azelaic acid: antibacterial, anti-inflammatory, anticomedogenic, mild to moderate inflammatory acne, irritant Antibiotics: inhibit the growth of p.acnes in moderate to severe inflammatory acne, topical mainly clindamycin & erythromycin solution, also available are dapsone(sulfon) solution & metronidazole gel. systemic antibiotics mainly minocycline, doxycycline & erythromycin.

Antibacterial agents Many gram positive & gram negative organisms infect the skin In gram positive infections as staphylococcal & streptococcal infections we can use topical antibacterial agents such as fucidin, mupirocin & bacitracin In gram negative infections as by E-coli, pseudomonas , & klebsiella we can use polymixin which is sometimes mixed with neomycin & bacitracin forming the “triple antibiotic”

Agents used for ectoparasites Mainly pediculosis & scabies, the most commonly used: 1- lindane: pediculicide & scabicide 2- permethrin in conc. 1% in pediculosis & 5% in scabies 3- synergized pyrithrins: pesticide with a substance to augment its effect, first line in pediculosis 4- crotamiton: scabicide & antipruritic with unknown mechanism of action 5- sulfur preparation in 5% & 10% concentrations are the best in scabies 6- oral ivermectin

Agents used for pigmentation Hyperpigmentation as chloasma & freckles, use temporary whitening preparations as hydroquinone in 2% & 4% concentration Inhibit tyrosinase enzyme involved in melanin synthesis Avoid higher concentration & longer duration due to risk of carcinogenicity Hypopigmentation as in vitiligo: methoxsalen is a photoactive substance (psoralen), stimulate melanocytes but needs UV radiation, forms the PUVA Inhibit DNA synthesis & cell differentiation Topical for small patches & systemic for large

corticosteroids They have anti-inflammatory & immunosuppressive effects Used for treating many itchy & inflammatory diseases like eczema & psoriasis They inhibit the arachidonic acid cascade, inhibit the production of cytokines & act on inflammatory cells Repeated use can lead to tachyphylaxis Different potencies as weak, medium strength, high strength & very high strength.

corticosteroids Side effects Skin atrophy, stria, purpura, acneiform rash, dermatitis, local infection & hypopigmentation In children potent steroids applied to a wide area can cause systemic effects as inhibiting the hypothalamic-pituitary-adrenal axis with ardrenal insufficiency & growth retardation

Trichogenic agents 1- minoxidil: originally oral antihypertensive, but noticed to increase hair growth as a side effect Very effective in androgenic alopecia (male & female pattern baldness) Available as a topical solution & shampoo Might shorten the rest phase in hair cycle Should be used continuously to exert its effect

Trichogenic agents 2- finasteride: an oral 5α reductase inhibitor preventing the conversion of testosterone to the active form 5α dihydrotestosteron (DHT) which play a key role in androgenic alopecia Side effects include decreased libido, ejaculation & erectile dysfunction Contraindicated in pregnancy as it may cause hypospadias in a male fetus