Drug eruptions Flashcards
prescription drug reaction rates
10 cases per 100 new users, higher with some classes of drugs- antimicrobials eastimated at 50 per 100 new users (PCN, cephalosporins, sulfonamides)
pathogenesis of a drug eruption
eruption beginning within 2 weeks of a new drug, supplement, or herb should be worked up as a possible drug reaction. 2 main mechanisms- immunologic (with 4 subtypes) and non- immunologic
non immunologic (predictable)
- pharmacologic side effect- dry mouth from antihistamine
- second pharmacologic- candidiadis from oral abx
- toxicity- hepatotoxicity from methotrexate
- drug interaction- seizure from theophylline from taking erythromycin
- nonimmunological activation of effector pathways- anyphylactiod reaction from radiocontrast
- overdose- excessive administration for person or condition, intentional or not inentional
non immunologic (unpredictable)
intolerance- tinnitis from ASA
idiosyncrasy- hemolytic anemia from dapsone
immunologic (unpredictable)
- IgE mediated- anaphylactic reaction to beta lactam abx
- cytotoxic- hemolytic anemia from PCN
- immune complex- serum sickness from tetanus antitoxin
- cell- mediated, delayed- contact dermatitis from nickel
- specific t-cell activation- exanthem from sulfonamides
- Fas/ Fas ligand induced- stevens johnsons syndrome, toxic epidermal necrolysis
- Misc- anticunvulsant hypersensitivity syndrome, Lupus- like syndrome
vital to the diagnosis and treatment of a drug reaction
accurate history!
- relationship of eruption to any rx meds, OTCs, supplements, vitamins, herbals
- onset, duration, pattern of eruption
- drug hx- when it was started, dosage changes, any interruptions in therapy
- look up whether drug is associated with reactions
most reliable way to determine the source of the eruption
Reintroduction- but this is dangerous and decision should not be made lightly. (Most drug eruptions will improve once the offending med is stopped)
patterns seen in cutaneous drug eruptions
basically anything- acneiform, alopecia, eczema, EM, erythema nodosum, exanthems, fixed eruption, lichenoid, photosensitivity, pigmentation, PR- like, purpura seb derm- like, toxic epidermal nocrolysis, urticarial vasculitis, vesiculobullous, lupus erythematosus- like
most common patterns seen in cutaneous drug eruptions
maculopapular (exanthemous eruptions, morbiliform)
urticarial
fixed drug eruptions
Exanthems (maculopapular) drug eruption
- most frequent of all cutaneous reactions (often indistinguishable from viral exanthems)
- typical from ampicillin and amoxicillin but pretty much any drug
- immunocompromised pts at increased risk
- sever rxns associated with: mucous membrane involvement, blisters, facial edema, lymphadenopathy,, temp higher than 101.3
Exanthems (maculopapular) clinical features
- red macules and papules that may come confluent
- distribution often symmetric, generalized (face often spared)
- can involve mucous membranes, palms, soles
- fever may be present at onset, labs can’t usually tell the diff between this and viral exanthum
- onset: 4- 21 days after start of drug
- duration: 1-3 weeks (sometimes fades even if drug isn’t stopped)
- rash clears quickly after med is stopped. May progress to generalized exfoliative dermatitis if med is continued
urticarial drug eruption- most frequent causes
ASA, PCNs, blood products
(most commonly associated with penicillins and derivatives)
*caution- almost all drugs have been associated
3 mechanisms of drug induced urticaria
- immunologic histamine release:
- IgE dependent- immediate (minutes) or accelerated (hours)
- anaphylactic mast cell degranulation occurs within minutes of drug exposure - nonimmunologic histamine release
- serum sickness
clinical features of urticarial drug eruptions
itchy
erythematous plaques with edema
usually generalized and symmetrical
no scaling or vesiculation
vary in size from small papules to huge plaques
typically fade within 24 hrs, often recur in another area
angioedema- urticarial swelling of deep dermal and subq tissue and mucous membranes- life threatening
fixed drug eruptions (FDE)
accounts for 25% of drug eruptions
reoccurs after each time the offending drug is administered
some reports of FDE on genitals associated with a drug taken by sexual partner