Leflunomide metabolite

Figure 10.2 Molecular structure of the Leflunomide metabolite A 77 1726 and the derivative A95 0277 which was successfully coupled to the activated Fractogel matrix used for affinity chromatography as well as to the BIAcore chip used for binding studies.

The results described in recent studies with differential proteomics approaches (Dax 1996 Dax et ah, 1998 Ortlepp et al, 1998 Kirschbaum et al., 1999 Mangold et al, 1999) finally lead to additional insight into the mode of action of Leflunomide (Arava), a new antiproliferative and immonoregulatory drug for the treatment of RA. In the present paper we show that affinity chromatography led to the identification of ten intracellular potential binding partners of the active Leflunomide metabolite A 77 1726. 

Manna, S. K., Aggaewal, B. B. (1999). Immunosuppressive Leflunomide metabolite (A77 1726) blocks TNF-dependent nuclear factor-kappa B activation and gene expression. 

Chan V, Charles BG, Tett SE. Rapid determination of the active leflunomide metabolite A77 1726 in human plasma by high-performance liquid chromatography. J Chromatogr B Analyt Technol Biomed Life Sci 2004 803(2) 331-5. 

The serum levels of the active metabolite of leflunomide are reduced by activated charcoal, and colestyramine. The manufacturers advise against the concurrent use of alcohol because of the potential for hepatotoxicity. Methotrexate may also increase leflunomide hepatotoxicity, so in general the combination is not recommended. A case of fatal fulminant hepatic failure has been reported in a patient taking leflunomide and itraconazole. A case of peripheral neuropathy has been reported in a patient taking leflunomide and tegafiir/uraciL The manufacturers predict interactions between leflunomide and phenytoin or tolbutamide, and advise caution with rifampicin as it may increase leflunomide metabolite levels. No clinically relevant interaction occurs with cime-tidine, corticosteroids or NSAIDs. 

The factors associated with a poor prognosis in leflunomide-induced lung injury have been studied in 22 patients with rheumatoid arthritis, of whom 9 died and 13 recovered [39 ]. The patients who died tended to have pre-existing interstitial pneumonia (8/9 vs. 6/13). The loading and maintenance doses, the serum concentration of the leflunomide metabolite A771726, and the duration of treatment did not differ between the groups. The patients who died had more frequent hypoxemia and mechanical ventilation, had a high serum CRP concentration (190 vs. 100 mg/1), and had a low albumin concentration (27 versus 33 g/1). The lymphocyte count was persistently low in those who died, but recovered in those who survived. 

The active metabolite of leflunomide, the ring-opened drug A771726, inhibits dihydroorotate dehydrogenase (DHOD) which is the key enzyme of the de novo pyrimidine synthesis. Inhibition of synthesis stops proliferation of activated lymphocytes. The leflunomide derivative FK778 which shows similar therapeutic efficacy but shorter half-life is investigated in clinical trials. 

Of interest here is that certain drugs and prodrugs that contain an isoxazole ring are metabolized to a cyano enol, e.g., leflunomide (11.122, R = CF3, R = H), a prodrug of the potential anti-arthritic agent 2-cyano-3-hydroxy-A-[4-(trifluoromethyl)phenyl]but-2-enamide (11.123). After oral administration of 50 mg/kg of 11.122 to rats, the plasma concentration of the prodrug peaked at 1 pg/ml and dropped rapidly, whereas the concentration of the active metabolite 11.123 was maintained at ca. 100 pg/ml for 24 h [147]. This... 

Leflunomide is a prodrug that is converted to an active malonitrilamide metabolite, A77 1726 (Ml). Ml inhibits T-cell proliferation by blocking de novo pyrimidine synthesis and inhibiting the tyrosine kinases that are associated with certain cytokine and growth factor receptors. 

Teriflunomide is the active metabolite of leflunomide (vide infra). It is in late-stage clinical development as potentially the first oral agent for multiple sclerosis. 

Leflunomide undergoes rapid conversion, both in the intestine and in the plasma, to its active metabolite, A77-1726. This metabolite inhibits dihydroorotate dehydrogenase, leading to a decrease in ribonucleotide synthesis and the arrest of stimulated cells in the Gi phase of cell growth. Consequently, leflunomide inhibits T-cell proliferation and production of autoantibodies by cells. Secondary effects include increases of interleukin-10 receptor mRNA, decreased interleukin-8 receptor type A mRNA, and decreased TNF-a-dependent nuclear factor kappa (NF- ) activation. 

Leflunomide is completely absorbed and has a mean plasma half-life of 19 days. A77-1726, the active metabolite of leflunomide, is thought to have approximately the same half-life and is subject to enterohepatic recirculation. Cholestyramine can enhance leflunomide excretion and increases total clearance by approximately 50%. 

Leflunomide is a prodrug of an inhibitor of pyrimidine synthesis rather than purine synthesis. It is orally active, and the active metabolite has a long half-life of several weeks. Thus, the drug should be started with a loading dose, but it can be taken once daily after reaching steady state. It is approved only for rheumatoid arthritis at present, though studies are under way combining... 

Pharmacokinetics Leflunomide is well absorbed after oral administration. It is extensively bound to albumin (>90 percent), and has a half-life of 14 to 18 days. [Note Because of its long half-life, loading doses are necessary (see p. 19).] Leflunomide is rapidly converted to the active metabolite. The metabolites are excreted in the urine and the feces. The active metabolite undergoes biliary recycling. 

In vivo, Leflunomide is rapidly converted into its pharmacologically active metabolite A77 1726 (Herrmann et al., 2000). Although the precise mode of action of Leflunomide in vivo remains elusive, A77 1726 has been shown in vitro to inhibit reversibly dihydro-orotate dehydrogenase (DHODH), which catalyzes a rate-limiting step in the de novo synthesis of pyrimidines (Cherwinski et al., 1995 Williamson et al., 1996). The inhibition of DHODH activity by A77 1726 might explain part of its mechanism of action in suppressing inflammation. 

Burger, D., Begue-Pastor, N., Benavent, S., Gruaz, L., Kauemann, M. T., Chicheportiche, R., Dayer, J. M. (2003). The active metabolite of Leflunomide, A77 1726, inhibits the production of prostaglandin E(2), matrix metalloproteinase 1 and interleukin 6 in human fibroblast-like synoviocytes. Rheumatology (Oxford) 42, 89-96. 

A77 1726, the active metabolite of Leflunomide does not block T-cell receptor-mediated signal transduction but its antiproliferative effects are antagonized by pyrimidine nucleosides. J. Heart Lung Transplant. 14,1016-1030. 

An interesting application of this interaction is seen with the use of leflunomide (Arava) in the treatment of rheumatoid arthritis. Leflunomide can cause fetal harm if administered during pregnancy, and it has an active metabolite that can persist in the system for at least 2 years. If a woman of childbearing potential discontinues use of leflunomide, it is recommended that cholestyramine (8 g 3 times a day for 11 days) be used to accelerate the elimination of the drug and its active metabolite. 

The prodrug leflunomide (A-(4 -trifluoromethylphenyl)-5-methylisoxazole-4-carboxamide) is an isoxazole derivative. Its main metabolite is the active compound, A77 1726 (1). 

A minor metabolite of leflunomide, 4-Trifluoromethyl-aniline, was mutagenic in vitro (87). 

In oral embryocytotoxicity and teratogenicity studies in rats and rabbits, leflunomide was embryocytotoxic (growth retardation, embryolethality) and teratogenic (malformations of the head, rump, vertebral column, ribs, and limbs) (87). Not only is leflunomide teratogenic and fetotoxic in animals, but its active metabolite is detectable in plasma up to 2 years after withdrawal. 

Schmidt A, Schwind B, Gillich M, Brune K, Hinz B. Simultaneous determination of leflunomide and its active metabolite, All 1726, in human plasma by high-performance liquid chromatography. Biomed Chromatogr 2003 17(4) 276-81. 

Leflunomide is a prodrug the active metabolite of which inhibits de novo pyrimidine synthesis and tyrosine kinase activity in T- and... 

B-lymphocytes. It is currently approved for use in rheumatoid arthritis. Bioavailability is 80% after oral administration. Leflunomide is metabolized in the liver to the active metabolite A77,1726. Biliary recirculation of A77,1726 contributes to the long half-life of 15 to 18 days. Adverse effects noted with leflunomide in solid-organ transplantation studies include skin rash, anemia, and elevated liver enzymes. 

Leflunomide was given to healthy women taking a triphasic oral contraceptive containing 30 micrograms of ethinylestradiol. During the study it was found that the leflunomide had no effect on the activity of the oral contraceptive and the pharmacokinetics of the active metabolite of leflunomide (A771726) were not changed to a clinically relevant extent. No special precautions would therefore appear to be needed on concurrent use. 

Studies in healthy subjects found that colestyramine 8 g three times daily reduced the serum levels of the active metabolite of leflunomide (A771726) by 48% after 24 hours and by 49 to 65% after 48 hours. 

The manufacturers advise caution if leflunomide is given with phenytoin or tolbutamide. The reason is that the active metabolite of leflunomide (A771726) has been shown by in vitro studies to be an inhibitor of the cytochrome P450 isoenzyme CYP2C9, which is concerned with the metabolism of these two drugs. If this inhibition were to occur in vivo it could possibly lead to a decrease in their metabolism and an increase in their toxicity. Although so far there appear to be no clinical reports of an interaction, the manufacturers made a similar prediction with warfarin, another CYP2C9 substrate, which has, in isolated cases, been borne out in practice. See Coumarins + Leflunomide , p.423. 

The manufacturers say that the concurrent use of leflunomide and other DMARDs (they list azathioprine, chloroquine, hydroxychloroquine, intramuscular or oral gold and penicillamine) has not yet been studied but they say that combined use is not advisable because of the increased risk of serious adverse reactions (haemo- or hepatotoxicity). As the active metabolite of leflunomide has a long half life of 1 to 4 weeks the manufacturers say that a washout of colestyramine or activated charcoal should be given if patients are to be started on other DMARDs. See also Methotrexate, below. 

When a single dose of leflunomide was given to subjects after taking multiple dose rifampicin, the peak levels of the active metabolite of leflunomide (A771726) were increased by 40% but the AUC was unchanged. - The reasons are not understood. There would seem to be no reason for avoiding concurrent use, but the manufacturers advise caution as A771721... 

More complex samples can be analyzed when IMS is coupled to MS. One example is the use of a Synapt traveling wave (TW) IMS for the metabolite profiling of leflunomide (LEF) and acetaminophen (APAP). Compared with quantitative (Q) TOF-MS and Q-TRAP-MS, the ability to provide mobility separation of the MS ... 

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