Antibody responses in man after single or repeated treatment with intramuscular ampicillin

Antibody responses to the penicilloyl moiety were recorded in patients treated intramuscularly with ampicillin for respiratory infections. For practical reasons this was performed at two clinics. At each clinic, two commercially available ampicillin preparations were used in a single-blind, randomised study. One of the preparations at each clinic was of high-grade purity and the other was slightly contaminated, according to a radioimmunoassay. There was the same heterogeneity in the patient material between the two clinics. The results showed a slight but significant (p less than 0.001) increase in IgM penicilloyl antibodies in the group of patients treated with the pure penicillin but not in those treated with the contaminated penicillin. When the patients in the two studies were analysed jointly, the increase in IgM antibodies was significantly greater (p less than 0.05) in the group treated with pure penicillin than in that treated with impure penicillin. The difference in antibody formation between the patient groups treated with pure or contamined ampicillin at each clinic was not significant, however. An immunological activity of the impurities suppressing the IgM antibody response is suggested.