Products derived from human serum have replaced the most frequently used antitoxins, rabies and tetanus horse serum antitoxins. The frequency and severity of reactions were found to be directly related to the amount and type of antiserum administered. Currently, nonprotein drugs are the most common cause of serum sickness-like reactions. Symptoms usually last 1-2 weeks before spontaneously subsiding. There are generally no long-lasting sequelae.
Fatalities are rare and are usually due to the continued administration of the antigen.
This may be due to the fact that older individuals received larger volumes of antitoxin. Primary serum sickness occurs 6-21 days after the administration of the inciting antigen. The onset may be more rapid with subsequent exposures to the same antigen, with symptoms occurring 1-4 days after exposure. The classic clinical manifestations consist of fever, arthralgia, lymphadenopathy and skin eruption. Pain, pruritus and erythematous swelling at the injection site usually precede the onset of disease.