Drug reactions can be classified in many ways. One useful approach is to separate predictable reactions occurring in normal patients from unpredictable reactions occurring in susceptible patients.
Predictable adverse reactions;
- Over dosage (wrong dosage or defect in drug metabolism)
- Side effects (sleepiness from antihistamines)
- Indirect effects (antibiotics changing normal flora)
- Drug interactions (altered metabolism of drugs; most commonly involving the cytochrome P-450 enzymes)
Unpredictable adverse reactions
- Allergic reaction (drug allergy or hypersensitivity; immunologic reaction to drug; requires previous exposure or cross-reaction)
- Pseudo allergic reaction (non-immunologic activation of mast cells).
- Idiosyncratic reaction (unexplained reaction, not related to mechanism of action, without known or suspected immunologic mechanism).
Note: 80% of allergic and pseudo allergic drug reactions are caused by Beta-lactam antibiotics, aspirin, NSAIDs, and sulfonamides
13.8.1 Fixed Drug Eruption (FDE)
It is a cutaneous drug reaction that recurs at exactly the same site with repeated exposure to the agent.
Diagnostic Criteria
- Typically red-brown patch or plaque
- Occasionally may be bullous
- Most common sites are genitalia, palms, and soles, as well as mucosa
- Lesions are typically 5–10cm in diameter but can be larger
- Often multiple. Starts with edematous papule or plaque later becomes darker
- Resolves with post-inflammatory hyperpigmentation
Note: When confronted with hyper pigmented macule on genitalia, always think of Fixed Drug Eruption
Non-Pharmacological Treatment
- Avoidance of triggering agent;
- Use of topical corticosteroids may speed resolution
Pharmacological Treatment
- Systemic corticosteroid, eg Prednisolone or Hydrocortisone
- Topical corticosteroid (as in eczemas)
- Oral antihistamines
13.8.3 Stevens Johnson Syndrome (SJS)
It is a rare but serious problem most often caused by reaction to medicines. It causes the skin to blister and peel off.
Diagnostic Criteria
- Abrupt development of erythema multiform
- Patients almost invariably have a prodromal with fever, malaise, and
arthralgia’s
- Erosions, hemorrhage and crusts on lips, and erosions in mouth covered by necrotic white pseudo membrane
- Involvement of the eyes in 70–90% of cases: Erosive conjunctivitis, can lead to scarring
- Involvement of genitalia in 60–70% of cases, with painful erosions
Pharmacological Treatment
- Admission,
- Close monitoring (fluids, Nutrition and electrolytes)
- Topical disinfection
- Prompt treatment of secondary infection.
Note: Systemic corticosteroids, if employed should be early, later in the course they increase the risk of infection and slow healing
13.8.4 Toxic Epidermal Necrolysis (TEN)
It is a severe life-threatening disorder with generalized loss of epidermis and mucosa. HIV disease increases the risk of developing TEN.
Diagnostic Criteria
- Prodrome of fever, stinging of eyes, and discomfort in swallowing.
- Sudden appearance of diffuse macules or diffuse erythema,
- Early sites of cutaneous involvement are the presternal region of the trunk and the face, but also the palms and soles.
- Involvement of the buccal, genital and/or ocular mucosae (with erythema and erosions) occurs in more than 90% of patients, and in some cases the respiratory and gastrointestinal tracts are also affected.
- Then prompt progression with widespread erythema and peeling of skin; skin lies in sheets and folds on the bedding.
Non-Pharmacological Treatment
- A critical element of supportive care is the management of fluid and electrolyte requirements
- Wounds should be treated conservatively, without skin debridement
Pharmacological Treatment
Patient has to be admitted for close care
B: Prednisolone (PO) 1–2mg/kg daily for 5–7 days.
A: Intravenous fluid should be given to maintain urine output of 50–80 mL per hour with 0.5% Sodium Chloride supplemented with 20 mEq of KCI.
Note: Ophthalmologic monitoring is essential, as risk of scarring and blindness is significant. Topical sulfa containing medications should be avoided and systemic corticosteroids, if employed, should be used early to attempt to abort the immunologic reaction (first 24 hours). Later in the course, they probably increase risk of infection and slow healing.
