Clinical trial of Ro 6-0787, a monovalent specific hapten inhibitor of penicillin allergy.

A second clinical trial of the compound Ro 6-0787, which is a specific monovalent penicilloyl hapten inhibitor of allergic reactions to penicillin has been conducted by investigators from 9 different European groups in 90 patients allergic to penicillin. The effect of a combined Ro 6-0787-penicillin therapy was considered as clinically successful in the large majority of cases, since treatment with penicillin could be pursued or resumed without allergic manifestation in 42 from 46 cases (91 percent). The effect of Ro 6-0787 alone on acute allergic manifestations after interruption of penicillin therapy was more difficult to evaluate but was nevertheless considered satisfactory in 17 from 26 patients (65 percent). A depression of skin hypersensitivity to PPL and/or penicillin and penicillin derivatives sometimes persisting for weeks and months was obvious in numerous allergic patients submitted to combined Ro 6-0787-penicillin treatment. A depressing effect on antipenicillin antibody titers detected by passive hemaglutination was also manifest in some patients. Failure to suppress allergic manifestations was reported in 11 cases, among which some may have been due to insufficient dosage of inhibiting hapten. The overall tolerance of Ro 6-0787 in allergic patients has been very good. Nevertheless, the major obstacle to a wider general use of Ro 6-0787 at the present time appears to be the occurrence of positive skin reactions to that compound in approximately 5 percent of patients allergic to penicillin. It is not yet ascertained whether the occasional positive skin reactions and urticaria to Ro 6-0787 may have been due to aggregation, or incomplete dissolution of the compound or whether it reflects hypersensitivity to another antigenic determinant. With the reservation that patients with positive skin test to Ro 6-0787 have for the time being to be excluded from combined treatment, this monovalent hapten certainly offers a new possibility to resume and/or pursue penicillin therapy in patients demonstrably allergic to that drug.