Myasthenia gravis caused by penicillamine and chloroquine therapy for rheumatoid arthritis

Drugs That Induce or Cause Deterioration of Myasthenia Gravis: An Update

Myasthenia gravis (MG) is an autoimmune neuromuscular disorder which is characterized by presence of antibodies against acetylcholine receptors (AChRs) or other proteins of the postsynaptic membrane resulting in damage to postsynaptic membrane, decreased number of AChRs or blocking of the receptors by autoantibodies. A number of drugs such as immune checkpoint inhibitors, penicillamine, tyrosine kinase inhibitors and interferons may induce de novo MG by altering the immune homeostasis mechanisms which prevent emergence of autoimmune diseases such as MG. Other drugs, especially certain antibiotics, antiarrhythmics, anesthetics and neuromuscular blockers, have deleterious effects on neuromuscular transmission, resulting in increased weakness in MG or MG-like symptoms in patients who do not have MG, with the latter usually being under medical circumstances such as kidney failure. This review summarizes the drugs which can cause de novo MG, MG exacerbation or MG-like symptoms in nonmyasthenic patients.

Effects of the quinoline derivatives quinine, quinidine, and chloroquine on neuromuscular transmission

The quinoline derivatives quinine, its stereoisomer quinidine, and chloroquine may worsen or provoke disorders of neuromuscular transmission. In this study, we investigate effects of these drugs on neuromuscular transmission by conventional microelectrode as well as patch-clamp techniques. At 5 x 10(-5) M, quinine, quinidine, and chloroquine reduced the quantal content of the end-plate potential by 37-45%. Between 10(-6) and 10(-4) M, all 3 drugs progressively decreased the amplitude and decay time constant of miniature end-plate potential (MEPP) and miniature end-plate current (MEPC); at 5 x 10(-3) M, the MEPP became undetectable. The effect on the MEPP was not reversed by 1 microgram/mL neostigmine. Single-channel patch-clamp analysis of the effects of quinine showed that this agent causes a long-lived open-channel as well as a closed-channel block of AChR. Tests for competitive inhibition or desensitization of the acetylcholine receptor (AChR) by quinine in concentrations that had a marked effect on the MEPC and on single-channel open and closed intervals were negative. Because quinoline drugs adversely affect both presynaptic and postsynaptic aspects of neuromuscular transmission at concentrations close to those employed in clinical practice, they should not be used, or used with caution, in disorders that compromise the safety margin of neuromuscular transmission.

New perspectives of secondary and tertiary therapy for rheumatoid arthritis

Rheumatoid arthritis continues to be recognised as a disorder with a variable prognosis, but recent studies have emphasised its potential for shortening life span. Epidemiological, genetic, and natural history studies have helped to identify patients who are at risk for the development of more aggressive disease earlier in their clinical course, and rheumatologists are willing to be more aggressive in their treatment now as their armamentarium expands. Earlier separation of drugs into anti-inflammatory and immunomodulatory agents becomes irrelevant as these concepts change and drugs fulfil both definitions. Sequences of therapy continue to be dictated by the potential of toxicity and generally follow rather than precede disease progression. The addition of several new agents to the algorithms of therapy against rheumatoid arthritis raises questions about their effects and place in therapeutic regimens, especially as concerns auranofin, sulphasalazine, methotrexate and cyclosporin. Combination therapy is currently at the end of the drug line, but the therapeutic horizon beckons with the potential of biological agents aimed at the restoration of immune balance.