A study of the utility of azathioprine metabolite testing in myasthenia gravis

Targeted Treatments for Myasthenia Gravis in Children and Adolescents

Myasthenia gravis (MG) is an antibody-mediated disorder of the neuromuscular junction affecting children and adults. MG is a treatable condition with most patients requiring immunosuppression for disease control and/or remission. Juvenile myasthenia gravis (JMG) is rare in comparison with adult-onset MG but given the same underlying pathophysiology, treatment strategies are similar to those in adults. Until recently, there were only a few randomised controlled trials (RCTs) for MG treatments in adults and none in children, and management strategies were primarily based on expert consensus. In addition, treatment options for refractory MG cases have been severely limited, resulting in poor long-term quality of life in such patients due to the significant disease burden. Recently, there have been several RCTs focussing on novel therapeutic strategies with potentially promising outcomes, suggesting a change in MG management over the coming years and access to more effective and faster-acting drugs for MG patients. This paper will review current and new MG treatments including efgartigimod, eculizumab, rozanolixizumab, ravulizumab, and zilucoplan, with a focus on juvenile myasthenia gravis.

Thiopurines' Metabolites and Drug Toxicity: A Meta-Analysis

Many questions remain unanswered regarding therapeutic drug monitoring (TDM) utility with thiopurines. This study aims to establish a relationship between thiopurines' metabolites and drug toxicity. We performed a systematic review with inclusion of studies evaluating the relationship between thiopurines' metabolites and drug toxicity. Meta-analysis of mean difference (MD), correlations and odds ratio (OR) was performed. We identified 21,240 records, 72 of which were eligible for meta-analysis. Levels of 6-thioguanine nucleotides (6-TGN) were higher in patients with leukopenia (MD 127.06 pmol/8 × 10⁸ RBC) and gastrointestinal intolerance (MD 201.46 pmol/8 × 10⁸ RBC), and lower in patients with hepatotoxicity (MD -40.6 pmol × 10⁸ RBC). We established a significant correlation between 6-TGN and leukocytes (r = -0.21), neutrophils (r = -0.24) and alanine aminotransferase levels (r = -0.24). OR for leukopenia in patients with elevated 6-TGN was 4.63 (95%CI 2.24; 9.57). An optimal cut-off of 135 pmol/8 × 10⁸ RBC for leukopenia was calculated (sensitivity 75.4%; specificity 46.4%). 6-methylmercaptopurine ribonucleotides (6-MMPR) were significantly associated with hepatotoxicity (MD 3241.2 pmol/8 × 10⁸ RBC; OR 4.28; 95%CI 3.20; 5.71). Levels of 6-MMPR measured in the first 8 weeks of treatment were associated with leukopenia. We conclude that TDM could be used to prevent thiopurines' toxicity. As optimal metabolites level may vary according to indication, physicians may adapt posology to decrease toxicity without compromising efficacy.

Relationship between Azathioprine metabolites and therapeutic efficacy in Chinese patients with neuromyelitis optica spectrum disorders

BACKGROUND

Neuromyelitis optica spectrum disorders (NMOSD) are demyelinating autoimmune diseases in the central nervous system (CNS) that are characterized by a high relapse rate and the presence of anti-aquaporin 4 antibodies (AQP4-IgG) in the serum. Azathioprine (AZA) is a first-line immunomodulatory drug that is widely used for the treatment of patients with NMOSD. However, the efficacy and safety of AZA vary in different individuals.

METHOD

Thirty-two patients with NMOSD who regularly took AZA were enrolled in the study at Beijing Tiantan Hospital, Capital Medical University. The efficacy of AZA was evaluated using the expanded disability status scale (EDSS) and the annual relapse rate (ARR). The erythrocyte concentrations of AZA metabolites were detected using an LC-MS/MS method.

RESULTS

The erythrocyte concentrations of 6-thioguanine nucleotides (6-TGNs) and 6-methylmercaptopurine nucleotides (6-MMPNs) were 202.03 ± 63.35 pmol/8*10⁸ RBC and 1618.90 ± 1607.06 pmol/8*10⁸ RBC, respectively. After the patients had received AZA therapy for more than one year, the EDSS score decreased from 5.21 ± 0.24 to 2.57 ± 0.33 (p < 0.0001), and the ARR decreased from 1.41 ± 0.23 to 0.36 ± 0.09 (p < 0.0001). The 6-TGN and 6-MMPN levels were significantly different between the non-relapsed and relapsed groups (p < 0.0001, p = 0.006, respectively). A higher ARR was significantly correlated with higher erythrocyte concentrations of 6-TGNs (p < 0.0001) and 6-MMPNs (p = 0.004).

CONCLUSION

AZA can reduce the EDSS score and ARR in NMOSD patients. Additionally, the efficacy of AZA is significantly related to the erythrocyte concentrations of 6-TGNs and 6-MMPNs. Within the safe upper limits, a higher concentration of 6-TGNs is associated with better efficacy of AZA.

TRIAL REGISTRATION NUMBER

ISRCTN16551495 , retrospectively registered on May 22, 2017.

What's in the Literature?

The Guillain-Barré syndrome (GBS) is one of the few neuropathies well known to the general public, in part because of its association with swine flu vaccinations in 1976. GBS has again reached the general public with its possible association with Zika virus. The virus, borne by infected Aedes aegypti mosquitos, is being linked to birth defects when pregnant women are bitten and infected. There are early reports also linking GBS to Zika infection, which could expose a wider range of infected people to the neuropathy. This summer infected Aedes mosquitos will likely reach southern portions of the United States, and travelers to countries where Aedes is endemic will increase. It is important to appreciate that the neurologic consequences of Zika virus are being actively investigated, and firm associations and consequences are yet to be established. Small fiber neuropathies are common and can be due to a number of underlying diseases, and a recent review also indicates that many are idiopathic. One cause is Sjögren syndrome, and a case series reviews clinical features. The diagnosis and underlying features of primary lateral sclerosis are a clinical challenge. Similarities between primary lateral sclerosis and hereditary spastic paraparesis (HSP) have long been noted. With a wide spectrum of gene mutations associated with HSP, clinical distinction between the 2 disorders is problematic. A review covers the wide spectrum of HSP. With no cure, the progression of amyotrophic lateral sclerosis (ALS) to respiratory failure is predictable. This could easily result in marked depression among patients, and 2 studies have explored the frequency and severity of depression. The cause of ALS remains unknown, and when no hereditary factor is apparent, environmental questions arise as possible contributing factor(s). The most notable association is with military service, although specific occupational or environmental linkages are not well sorted out. Two recent reports address these issues. There is good news for ALS patients with muscle cramps with the results of a multicenter randomized and placebo-controlled trial showing that mexiletine is effective in reducing this common symptom. The treatment of myasthenia gravis with various agents, the use of patient-reported outcome measures in myasthenia gravis, and the occurrence of myocarditis in this disease are reviewed. Necrotizing autoimmune neuropathies, the co-occurrence of inclusion body myositis and a form of T-cell leukemia are discussed as are valosin-containing protein (VCP)-opathy and bone health in patients with dystrophinopathy.