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
Morbilliform:
- 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
![morbilizim](http://medicalcareone.com/wp-content/uploads/2020/05/morbil-e1592197189721.png)
Urticarial
- 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
![](http://medicalcareone.com/wp-content/uploads/2020/05/urticarlar.png)
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
![](http://medicalcareone.com/wp-content/uploads/2020/05/fixed-drug-irruption.png)
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
![](http://medicalcareone.com/wp-content/uploads/2020/05/polymorphos.png)
Photo toxicity
- It occurs with ingestion of certain chemicals or drugs
- It presents with exaggerated severe sun burn after minor exposure
Photosensitivity
- Typically occurs after topical application of a sensitizing agent
- It causes itchy eczema like eruption
![](http://medicalcareone.com/wp-content/uploads/2020/05/photo-toxicity-e1592197298575.png)
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
![](http://medicalcareone.com/wp-content/uploads/2020/05/hypersinsitivity.png)