Module 11 - Skin, Eyes, and Ears

Layers of the Skin

Epidermis (outermost, from outside in)

• Stratum corneum - outermost, primary barrier

• Stratum lucidum - thin; only in thick-skin areas (palms, soles)

• Stratum granulosum - where cells begin to die

• Stratum spinosum - thickest layer; contains keratinocytes

• Stratum basale - deepest epidermal layer; location of melanocytes

Dermis

• Second layer; makes up 95% of skin thickness

• Contains nerve endings, oil glands, sweat glands, blood vessels

• Foundation for hair and nails

Subcutaneous layer

• Third layer; composed of adipose tissue

• Cushions, insulates, and stores energy

• Not counted when measuring skin layers

Topical Drug Delivery

Low absorption

• Drug remains in skin → local effect only

• Example: lidocaine topical anaesthetic

High absorption

• Drug crosses skin into bloodstream → systemic effect

• Example: fentanyl transdermal patch

Skin Disorder Classifications

Infectious

• Bacterial - boils, impetigo, infected hair follicles

• Fungal - ringworm, athlete's foot, jock itch, nail infections

• Parasitic - ticks, mites, lice

• Viral - herpes simplex, shingles, chickenpox, warts, measles

Inflammatory

• Sun exposure, overactive glands, infection - acne, rosacea

• Itching and cracking disorders - atopic dermatitis, psoriasis

Neoplastic

• Malignant - squamous cell carcinoma, basal cell carcinoma, malignant melanoma

• Benign - keratosis, keratoacanthoma

Bacterial Skin Infections

Occur when there is a break in the skin's defences.

• Most common organisms: Staphylococcus and Streptococcus

• Usually mild and self-limiting

Serious infections

• Deep or systemic infections require oral or parenteral antibiotics

Common topical antibiotics

• Bacitracin, gentamicin, erythromycin, tetracycline

• Variety of mechanisms - from cell lysis to inhibition of synthetic enzymes

Fungal Skin Infections

Occur in warm, moist areas of skin.

• Tinea pedis - athlete's foot

• Tinea cruris - jock itch

• Tinea capitis - ringworm of the scalp

• Tinea unguium - nail infection

• Treated with topical antifungals (clotrimazole or miconazole)

Viral Skin Infections

Childhood infections

• Varicella (chickenpox)

• Rubeola (measles)

• Rubella (German measles)

• Typically controlled via prophylactic vaccination

Adult infections

• Herpes zoster (shingles)

• Herpes simplex - cold sores and genital lesions

Treatment - Acyclovir (Zovirax)

• Available topically or orally

• Mimics guanine → incorporated into viral DNA synthesis → shuts it down

Parasitic Skin Infections

Mites (Sarcoptes scabiei) - scabies

• Not visible to the naked eye

• Female burrows into skin and lays eggs → intense itching

• Common areas: fingers, extremities, trunk, axillary/gluteal folds, pubic area

• Spread by contact with upholstery, linens, or direct body contact

Norwegian scabies

• Advanced infection; almost exclusively in immunocompromised or age >65

• Crusts contain millions of mites; topical scabicides ineffective

• Requires long-term oral ivermectin

Lice (Pediculus/Pthirus)

• Visible to the naked eye

• Infest hair-bearing areas; lay eggs (nits); transmitted by clothing or contact

• Cause intense itching

Key distinction

• Scabicides = treat mites; pediculicides = treat lice (some drugs do both)

Acne Vulgaris

Disorder of hair follicles and sebaceous glands

Lesions called comedones - open (blackheads) or closed (whiteheads)

Four interconnected causes

• Excess sebum production (seborrhea)

• Proliferation of Cutibacterium acnes in hair follicles

• Overgrowth of keratinocytes that plug the follicle

• General inflammatory immune response triggered by the above three

Acne Pharmacotherapy

Topical agents

• Retinoids - tretinoin, adapalene, tazarotene; prevent follicular plugging

• Antibiotics - clindamycin, erythromycin; reduce C. acnes colonization

• Keratolytics - benzoyl peroxide, salicylic acid; shed epidermis, suppress sebum, antibacterial

Oral agents

• Isotretinoin - severe cystic acne; serious teratogen; iPLEDGE/RMP program required

• Antibiotics - tetracyclines (doxycycline); reduce C. acnes

• Contraceptives - reduce androgen-driven sebum production

Mechanistic targets

• Inhibit sebaceous gland overactivity

• Reduce bacterial colonization

• Prevent follicular plugging with keratin

• Reduce inflammation

Tretinoin (Retin-A)

Early treatment and control of mild to moderate acne vulgaris: cystic acne or severe keratinization disorders.

Timeline: 4-8 weeks to improve; maximum benefit at 5-6 months

Isotretinoin (Accutane)

Oral formulation of tretinoin; used for severe cystic/nodular acne

Serious teratogenic effects.

Benzoyl Peroxide and Salicylic Acid

Most common OTC topical acne treatments; available as lotion, cream, or gel

Mechanisms

• Keratolytic effect - dries and sheds the outer epidermal layer

• Suppresses sebum production

• Exhibits antibacterial activity against C. acnes

Rosacea

Small papules without pus; flushed face around nose and cheeks

Rhinophyma - soft tissue swelling of the nose

Exacerbated by sunlight, stress, and vasodilatory agents (alcohol, some skincare)

Women disproportionately affected.

Metronidazole (first line)

• Forms a radical species that damages microbial DNA

• No alcohol while taking

Azelaic acid (first line)

• Multi-mechanism: antibacterial and radical scavenging

Dermatitis

Excoriation - scratches fill with blood/serous fluid forming crusty scales

Atopic dermatitis (eczema)

• Chronic; genetic predisposition

Contact dermatitis

• Hypersensitivity response to a contact trigger

• Not the same as urticaria (hives)

Seborrheic dermatitis

• Seen in newborns (cradle cap) and teenagers post-puberty

• More oily appearance than other dermatitis types

Pharmacotherapy

• High potency (e.g., clobetasol)

  • Acute flare-ups only; limit to 2-3 weeks

  • Avoid high-absorption areas (face, groin, axilla)

  • Do not apply occlusively

• Medium potency (e.g., triamcinolone)

  • More prolonged therapy for chronic dermatitis

  • Still best to avoid high-absorption areas

• Low potency (e.g., hydrocortisone)

  • Used in children

  • Safe for high-absorption areas

• All potencies

  • Never apply directly onto infected skin

  • Skin atrophy is a risk regardless of strength

Psoriasis

Chronic inflammatory disorder; no known cure

Red patches covered with flaky silver scales (plaques) caused by increased cell turnover

Topical (first line)

• High-potency corticosteroids for acute flare-ups (2-3 weeks)

• Medium/low-potency for chronic maintenance

Neoplastic

Uncontrolled growths of the skin, most commonly in the form of skin cancers.

May be benign (not cancerous, not spreading) or malignant (cancerous, spreading).

Eye Structure and Function

Aqueous humour secreted by the ciliary body in the posterior chamber.

Flow

• Flows from the posterior chamber through the pupil into the anterior chamber

• Passes through the trabecular meshwork into the canal of Schlemm → drains out

Glaucoma

Occurs when there is increased intraocular pressure (IOP) that causes pressure to be placed on the optic nerve.

Open-angle (90% of cases)

• Usually bilateral

• IOP rises gradually and asymptomatically over years

• Iris does not cover the drainage angle → outflow only reduced

• Can be treated pharmacologically

Closed-angle (rare)

• Usually unilateral

• IOP rises very rapidly over hours

• Iris fully covers anterior chamber angle → no drainage possible

• Highly symptomatic: severe eye pain, headache, blurred vision, dizziness, fixed pupil

• Medical emergency - requires immediate nonpharmacological intervention

Prostaglandin Analogues

Mimic naturally occurring prostaglandins, which are locally acting lipid

signaling molecules.

Relax smooth muscle of the trabecular meshwork, widening the drainage pathway.

Increase outflow of aqueous humour.

Beta-Adrenergic Antagonists

Block beta receptors in the ciliary body epithelium

Reduce active secretion of aqueous humour - decrease production

Same mechanism as oral beta blockers for hypertension/arrhythmias

Alpha2-Adrenergic Agonist

Agonize alpha-2 receptors in the cilary body.

Reduce active secretion of aqueous humour — decrease production

Carbonic Anhydrase Inhibitors

• Inhibit carbonic anhydrase in the ciliary body → reduce bicarbonate/fluid secretion → decrease production

• Topical (dorzolamide) minimizes systemic effects

• Oral/IV (acetazolamide): diuresis, electrolyte imbalances, blood dyscrasias

Cholinergic Agonists

Activate muscarinic receptors → miosis and ciliary muscle contraction → open trabecular meshwork → increase outflow

Older class; less commonly used due to visual side effects

Osmotic Diuretic

↑ plasma osmolality → draw fluid out of the eye by osmotic gradient → rapid IOP reduction

Reserved for acute situations (closed-angle glaucoma); not for chronic use

Miscellaneous Eye Therapy

Mydriatic drugs

• Cause pupillary dilation for eye examinations

Cycloplegic drugs

• Dilate the pupil and paralyze the ciliary muscle for refraction testing and eye exams

Lubricants and vasoconstrictors

• Treat eye irritation and redness

Ear Structure and Function

External otitis - inflammation of the outer ear; treated wiht topical antibiotics (ciprofloxacin)

Otitis media - inflammation of the middle ear; treated with oral systemic antibiotics (ciprofloxacin, amoxicillin)

Mastoiditis - inflammation of the mastoid sinus; treated with more aggressive IV/oral antibiotics (gentamycin)