Gold and penicillamine: a proposed mode of action in rheumatoid arthritis, based on synovial fluid analysis.

Although in common use, there is still controversy as to the way in which gold and penicillamine act in rheumatoid arthritis (RA). In this study, synovial fluids from 4 groups of patients have been compared: (1) RA patients on gold/penicillamine, (2) RA patients on non-steriodal anti-inflammatory drugs (NSAID) only, (3) osteoarthritis patients, and (4) patients with sero-negative arthropathies. The parameters measured were differential agglutination titre (DAT), total haemolytic complement (CH50), total protein, total white cell count, and immunoglobulins. RA patients on gold/penicillamine have lower synovial DAT levels and higher CH50 levels than RA patients on NSAID only, and total and cryoprecipitable IgM levels very close to those found in the sero-negative joint fluids. The non-specific inflammatory parameters, ie, white cell count and total protein are unchanged after good/penicillamine therapy. In a second study, the serum DATs of patients in total remission after gold/penicillamine were compared with similar patients on NSAID only. The DAT falls significantly in the former group (P less than 0.001), but not in the latter suggesting that fall in DAT is a consequence of therapy rather than remission. The parameters altered by gold/penicillamine in the synovial fluid are those that distinguish RA from non-rheumatoid arthropathies suggesting the drug's primary effect is to render the disease sero-negative. The results support the hypothesis that both drugs have a common mode of action based on their active thiol groups, and that the fall in DAT is due to the reduction of the antigenicity of the IgG complexes.