Drug Reactions

Drug reactions can be classified to:

  • Morbilliform (Measles like) most common
  • Urticarial (hives) second most common
  • Fixed drug
  • Photo sensitivity
  • Hypersensitivity Vasculitis
  • Severe reactions including Stevens Johnsons Syndrome


  • Most common drug reaction
  • It is type IV hypersensitivity reaction
  • It starts 1-2 weeks after drug ingestion-sooner if reused in the future
  • It causes pink bumps and patches that coalesce to form large lesions
  • It spares the palms and soles
  • Taking Amoxil when having Infectious Mono can produce this type of reaction

Treatment: Stop the drug, antihistamine and steroids



  • Second most common drug reaction
  • Type I hypersensitivity with IgE mediated release of histamines
  • It starts within minutes to hours after exposure
  • It causes Weals/hives with some skin swelling and itching
  • In severe cases it may cause Anaphylactic Reaction with throat swelling and drop in blood pressure and can be life threatening

Treatment:if severe—> Epinephrine injection (EpiPen)
                 If mild to moderate—>Antihistamines and steroids

Fixed Drug Eruption

  • The rash recur at the same skin site with each repeated exposure
  • It usually found on lips, face, fingers and genitals
  • It causes a pink to purple bump with central dusky discoloration that may turn to blister
  • Lesions resolve with muddy brown post inflammatory hyperpigmentation

Polymorphous Light Eruption

  • Most common idiopathic photosensitivity disorder
  • It occurs in spring and early summer
  • It persists for weeks and resolves without scarring even with continuous sun exposure

Photo toxicity

  • It occurs with ingestion of certain chemicals or drugs
  • It presents with exaggerated severe sun burn after minor exposure


  • Typically occurs after topical application of a sensitizing agent
  • It causes itchy eczema like eruption

Hypersensitivity Vasculitis

  • It is a small vessel Vasculitis
  • It causes palpable bleeding spots under the skin (Purpura or Petichiae)
  • It may be associated with fever, Joints pain and swollen lymph nodes