Call your doctor for concerns after surgery: Morbilliform drug reaction

Morbilliform drug reaction

What is morbilliform drug reaction?

Morbilliform drug eruption is the most common drug hypersensitivity reaction. Many drugs can trigger this allergic reaction, but antibiotics are the most common group. The eruption may resemble rashes or exanthems caused by viral and bacterial infections.

It is also called maculopapular drug eruption, morbilliform exanthem and maculopapular exanthem.

Who gets it?

Morbilliform drug eruptions are very common, comprising 95% of all drug-induced skin reactions. Beta-lactam antibiotics (penicillins, cephalosporins), antibiotic sulfonamides, allopurinol, anti-epileptic drugs and nonsteroidal anti-inflammatory drugs (NSAID) are the most common drugs to cause this. However the list is very long and includes herbal and natural therapies.

On the first occasion, the skin rash usually appears 1-2 weeks after starting the drug, but sometimes may occur up to 1 week after ceasing the medication. However on re-exposure to the causative (or related) drug, skin lesions appear within 1-3 days.

In general, a morbilliform skin rash in an adult is usually due to a drug, but in a child is more likely to be viral.

The development of a morbilliform eruption after starting amoxicillin for sore throat and fever is almost diagnostic for glandular fever (infectious mononucleosis), occurring in almost 100%.

Clinical features

Morbilliform drug eruption usually first appears on the trunk and then spreads to the limbs and neck in a symmetrical pattern. Mucous membranes are not affected.

The exanthem consists of widespread pink-to-red flat spots (macules) or raised bumps (papules) that blanch with pressure. It may resemble the rash of measles, rubella or scarlet fever, thus mimicking viral and bacterial exanthems. The spots may cluster and merge to form sheets over several days, sometimes involving the entire skin surface. On the lower legs the spots may appear purple and non-blanchable (purpura), especially if the patient has a low platelet count. On the extremities the spots may appear ring-shaped (annular) or hive-like (urticaria-like), giving a polymorphous (mixed) appearance, a clue that this is a drug reaction and not due to infection.

The rash may be associated with a mild fever and itch.

Treatment

Often times patients can develop this presentation with use of prophylactic antibiotics, and the best course of action is to discontinue the medication if possible immediately. Other times ancillary treatment may also be useful such as prednisone, cremes, diphenhydramine, and referral to allergist for severe cases.