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Residual activity of microencapsulated permethrin against stable flies on lactating dairy cows.

Meyer JA, Hunter JS 3rd.

Department of Entomology, University of California, Riverside 92521.

Emulsifiable concentrate and microencapsulated formulations of permethrin were evaluated for residual activity against stable flies on lactating dairy cows. Cows were treated in the field with each formulation and hair was clipped from the leg and shoulder area, and bioassayed at 1, 2, 3, 4, 7 and 14 days after treatment. Significantly more stable flies died when exposed to hair sampled 3, 4 and 7 days after treatment from the shoulder than from the lower leg. Analysis with gas chromatography of hair samples showed no detectable permethrin residues on shoulder or leg hair 72 h after treatment with the emulsifiable concentrate formulation. Microencapsulated permethrin was still detectable on hair sampled from both locations 7 days after treatment. The permethrin concentration on the leg hair was approximately 50% of the shoulder hair concentration after 3 days, with the leg hair residue dropping to 31% of shoulder level after 7 days.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=1768927&dopt=Abstract permethrin Elimite



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Induction of cytochrome P450 2B1 by pyrethroids in primary rat hepatocyte cultures.

Heder AF, Hirsch-Ernst KI, Bauer D, Kahl GF, Desel H.

Department of Toxicology, Institute of Pharmacology and Toxicology, University of Goettingen, Robert-Koch-Str. 40, D-37075, Goettingen, Germany. aheder med.uni-goettingen.de

Numerous xenobiotics are capable of inducing their own metabolism and by enzyme induction can also lead to enhanced biotransformation of other xenobiotics. In this project, we examined the influence of pyrethroids (permethrin, cypermethrin, and fenvalerate) on the expression and activity of the phenobarbital (PB)-inducible cytochrome P450 2B1 isoform (CYP2B1) in primary rat hepatocyte cultures. Incubation of hepatocyte cultures with pyrethroids resulted in a marked CYP2B1 induction. Among the tested pyrethroids, permethrin elicited the most pronounced induction of CYP2B1 mRNA, which exceeded maximal induction achieved by PB at concentrations approximately 10-fold higher. Furthermore, permethrin induced CYP3A1 mRNA expression, while the expression of the CYP1A1 isoform, which in vivo is not responsive to PB treatment, was not significantly affected by pyrethroids. Permethrin-dependent enhancement of CYP2B1 and CYP3A1 mRNA expression was repressed by the hepatotrophic cytokine epidermal growth factor, which is known to also inhibit PB-dependent induction of CYP2B1. Several metabolites of permethrin formed by hepatocytes (3-(2',2'-dichlorovinyl)-2,2-dimethylcyclopropanecarboxylic acid, 3-phenoxybenzyl alcohol, and 3-phenoxybenzoic acid) were ineffective in inducing CYP2B1 mRNA. Furthermore, permethrin stimulated the expression of the luciferase reporter gene under control of the CYP2B1 promoter (comprising the PB-responsive enhancer module) in transiently transfected primary hepatocyte cultures. Thus, permethrin-stimulated gene expression occurred on the transcriptional level. Taken together, these results indicate that the pyrethroid permethrin is a PB-like inducer. Due to its superior potency in induction, permethrin appears as a useful substance for mechanistic studies to elucidate the mechanism of enzyme induction by phenobarbital.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11377398&dopt=Abstract permethrin Elimite



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Acute toxicity of permethrin to four size classes of red swamp crayfish (Procambarus clarkii) and observations of post-exposure effects.

Jarboe HH, Romaire RP.

School of Forestry, Wildlife, and Fisheries, Louisiana State University Agricultural Center, Baton Rouge 70803.

The mean static acute 96-h LC50 of permethrin [(3-phenoxybenzyl (+) cis, trans, 3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropane carboxylate)] to red swamp crayfish (Procambarus clarkii) 8-12 mm (0.017 g), 25-35 mm (0.64 g), 45-55 mm (2.45 g), and 65-75 mm total length (8.98 g) was 0.44, 0.85, 1.30, and 0.81 micrograms/L, respectively. Permethrin toxicity did not differ among immature or mature male and female P. clarkii. Crayfish surviving permethrin exposures exhibited no differences in post-exposure growth, survival, onset of sexual maturity, or the reproduction of viable young when compared to non-exposed controls. Teratogenesis was not observed in third-instar crayfish produced from permethrin-exposed parents.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=1859206&dopt=Abstract permethrin Elimite



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Toxicokinetics of permethrin in the rat.

Anadon A, Martinez-Larranaga MR, Diaz MJ, Bringas P.

Institute of Pharmacology and Toxicology, CSIC, Department of Pharmacology, Faculty of Medicine, Universidad Complutense, Madrid, Spain.

The toxicokinetics of permethrin after single 460 mg/kg oral and 46 mg/kg intravenous doses were studied in male Sprague-Dawley rats. Serial blood samples after oral and intravenous dosage, and brain, medulla oblongata, sciatic nerve, and liver samples after oral administration were collected. Plasma, hypothalamus, cerebellum, frontal cortex, caudate putamen, hippocampus, medulla oblongata, sciatic nerve, and liver concentrations of permethrin and its metabolites, m-phenoxybenzyl alcohol and m-phenoxybenzoic acid, were determined by a high-performance liquid chromatographic assay. The permethrin plasma profile could be adequately described by a two-compartment open model. For permethrin, the elimination half-life (t1/2 beta) and the mean residence time from plasma were 8.67 and 11.19 hr after i.v. and 12.37 and 17.77 hr after po administration. The total plasma clearance was not influenced by dose concentration or route and reached a value of 0.058 liter/hr. After the single oral dose, permethrin was absorbed slowly with a Tmax of 3.52 hr. The maximum plasma concentration was 49.46 micrograms/ml. The oral bioavailability of permethrin was found to be 60.69%. The plasma concentration-time data for permethrin metabolites as well as the tissue concentration-time data for permethrin and its metabolites after an oral dose of permethrin were found to fit a one-compartment open model. The elimination half-life (t1/2el) of permethrin was greater for the hippocampus, medulla oblongata, frontal cortex, and sciatic nerve (23.10, 22.36, 13.86, and 16.27 hr, respectively) than for plasma (t1/2 beta, 12.37 hr). The maximum amounts of permethrin in cerebellum, hippocampus, caudate putamen, frontal cortex, hypothalamus, and sciatic nerve were about 1.5, 2, 2, 2.7, 4.8, and 7.5 times higher than in plasma, respectively, indicating an accumulation of pyrethroid by nervous tissue itself. Nervous tissue accumulation of permethrin was also reflected by the area under the concentration curve ratios of tissue/plasma (1.16, 3.71, 1.57, 4.27, 3.48, and 8.77, respectively). The metabolites of permethrin, m-phenoxy-benzyl alcohol and m-phenoxybenzoic acid, were detected in plasma and in all selected tissues for 48 hr after dosing, suggesting that a combination of metabolism by the tissues and diffusion into it from the blood may be present.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=1871768&dopt=Abstract permethrin Elimite



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Deet and permethrin as protectants against malaria-infected and uninfected Anopheles stephensi mosquitoes.

Robert LL, Schneider I, Wirtz RA.

Department of Entomology, Walter Reed Army Institute of Research, Washington, DC 20307-5100.

Deet and permethrin were evaluated as protectants against Plasmodium falciparum-infected, P. berghei-infected and uninfected Anopheles stephensi mosquitoes. Deet 50% effective dose (ED50) values were 3.2 micrograms/cm2 for P. falciparum-infected and 1.9 micrograms/cm2 for uninfected mosquitoes; permethrin values were 0.5 micrograms/cm2 and 0.6 micrograms/cm2, respectively. Deet ED50 values were 2.3 micrograms/cm2 for P. berghei-infected and 1.3 micrograms/cm2 for uninfected mosquitoes; the permethrin values were both 0.5 micrograms/cm2. There were no significant differences in the protective efficacy of deet or permethrin between malaria-infected and uninfected An. stephensi mosquitoes.

Online source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=1895090&dopt=Abstract permethrin Elimite