CHAPTER 17 CUTANEOUS ADVERSE DRUG REACTION 275
EM: respiratory infection and internal neoplasia (especially thymoma in cats).
Thermal or chemical burns may give similar clinical appearance.
DIAGNOSTICS
Serum biochemistry and complete blood count (especially when cutaneous vasculitis
is suspected or diagnosed: potential for concurrent hepatic, renal, and gastrointestinal
disease).Rickettsial serology, ANA.
Cats: FIV and FeLV serology.
Bacterial and fungal cultures and sensitivity testing (especially if pyogranulomatous
inflammation is a clinical feature).
Biopsy: CADR – may be nonspecific and/or specific to a drug-induced syndrome:
EM – hyperkeratosis and parakeratosis (especially noted in “old dog” EM); cytotoxic
(interface) dermatitis with apoptosis (cell death) in both suprabasilar and basilar
cell layers; apoptosis with lymphocyte satellitosis is prominent in the upper layers
of the epidermis as well as affecting the follicular infundibular epithelium: SJS/TEN –
interfollicular and follicular infundibular cytotoxic dermatitis with apoptosis; more
extensive than EM and progressing to full-thickness coagulative epidermal necrosis;
separation of necrotic epidermis from the dermis; lack of dermal necrosis differenti-
ates from thermal burn.THERAPEUTICS
Discontinue use of the potential offending drug.
SJS/TEN: intensive supportive care and fluid/nutritional support because of fluid and
protein exudation and risk of sepsis; pain control.
Corticosteroids: controversial; early/high then tapering dosage.
Cyclosporine (5 mg/kg/day).
Oclacitinib (0.4–0.6 mg/kg q24h to BID); may reduce T cell response.
Tacrolimus applied to lesions (feline).
Azathioprine 50 mg/m^2 /day tapering dosage (canine).
Human intravenous immunoglobulin (IVIG) may be helpful in refractory cases.
Pentoxifylline (Trental) may be helpful in some cases.
COMMENTS
Inpatient: if debilitated.
Outpatient: regular rechecks, depending on physical condition.
Some reactions appear to activate self-perpetuating immune responses.
Some drug metabolites may persist for days to weeks and provoke a continued
response.
Vasculitis: prognosis guarded when there are systemic complications associated
with arthropathy, hepatitis, glomerulonephritis, and neuromuscular disorders, among
others.Prognosis: EM good to poor; SJS poor to guarded; TEN guarded to grave.