The trans enantiomeric pair is known as transpermethrin. (1R,3S)-trans and (1R,3R)-cis enantiomers are responsible for the insecticidal properties of permethrin. History
Permethrin was first made in 1973.Numerous synthetic routes exist for the production of the DV-acid ester precursor. The pathway known as the Kuraray Process uses four steps. In general, the final step in the total synthesis of any of the synthetic pyrethroids is a coupling of a DV-acid ester and an alcohol. In the case of permethrin synthesis, the DV-acid cyclopropanecarboxylic acid, 3-(2,2-dichloroethenyl)-2,2-dimethyl-, ethyl ester, is coupled with the alcohol, m-phenoxybenzyl alcohol, through a transesterification reaction with base. Tetraisopropyl titanate or sodium ethylate may be used as the base.The alcohol precursor may be prepared in three steps. First, m-cresol, chlorobenzene, sodium hydroxide, potassium hydroxide, and copper chloride react to yield m-phenoxytoluene. Second, oxidation of m-phenoxytoluene over selenium dioxide provides m-phenoxybenzaldehyde. Third, a Cannizzaro reaction of the benzaldehyde in formaldehyde and potassium hydroxide affords the m-phenoxybenzyl alcohol. Brand names
In Nordic countries and North America, a permethrin formulation for lice treatment is marketed under trade name Nix, available over the counter. Johnson & Johnsons UK brand Lyclear covers an assortment of different products, mostly non-insecticidal, but a few of which are based on permethrin.Stronger concentrations of permethrin are used to treat scabies (which embed inside the skin), compared to lice (which remain outside the skin). In the U.S. the more concentrated products such as Elimite are available by prescription only. Other animals
It is known to be highly toxic to cats, fish and aquatic species with long-lasting effects.
Although the majority of cases initially respond well to treatment, relapses are not uncommon and immunosuppressive drugs (e.g. ciclosporin, mycophenolate mofetil, vincristine and danazol) are subsequently used, or combinations of these.The off-label use of rituximab (trade name Rituxan) has produced some good results in acute and refractory cases, although further relapse may occur within a year. Splenectomy is effective in some cases, but relapses are not uncommon.The only prospect for a permanent cure is the high-risk option of an allogeneic hematopoietic stem cell transplantation (SCT). Prognosis
In a nationwide study of Evans syndrome the median survival was 7.2 years (primary Evans syndrome: 10.9 years; secondary Evans syndrome: 1.7 years). Secondary Evans syndrome was associated with higher mortality rate than primary Evans syndrome, with a 5-year survival of 38%. Among patients with Evans syndrome, the prevailing causes of death were bleeding, infections, and hematological cancer.It has been observed that there is a risk of developing other autoimmune problems and hypogammaglobulinemia, in one cohort 58% of children with Evans syndrome had CD4-/CD8- T cells which is a strong predictor for having autoimmune lymphoproliferative syndrome. Epidemiology
Evans syndrome is considered a very rare autoimmune disease. Only one study has estimated incidence and prevalence adults. In Denmark in 2016 the annual incidence was 1.8 per 1,000,000 person years, and the prevalence was 21.3 per 1,000,000 living persons. In pre-pubertal children the incidence has been estimated to be between  0.7 and 1.2 per 1,000,000 person-years. See also
Hematology

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