Severe serum sickness reaction to oral and intramuscular penicillin.

Serum sickness is a type III hypersensitivity reaction mediated by immune complex deposition with subsequent complement activation, small-vessel vasculitis, and tissue inflammation. Although the overall incidence of serum sickness is declining because of decreased use of heterologous sera and improved vaccinations, rare sporadic cases of serum sickness from nonprotein drugs such as penicillins continue to occur. Drug-induced serum sickness is usually self-limited, with symptoms lasting only 1-2 weeks before resolving. We report an unusual case of a severe and prolonged serum sickness reaction that occurred after exposure to an intramuscular penicillin depot injection (probable relationship by Naranjo score) and discuss how pharmacokinetics may have played a role. Clinicians should be familiar with serum sickness reactions particularly as they relate to long-acting penicillin preparations. Accurate diagnosis in conjunction with cessation of drug exposure and prompt initiation of antiinflammatory treatment with corticosteroids can produce complete recovery