Tissue time course and bioavailability of the pyrethroid insecticide bifenthrin in the Long-Evans rat

Successful treatment of bifenthrin toxicosis using therapeutic plasma exchange

OBJECTIVE

To describe a case of bifenthrin toxicosis in a dog with a successful outcome following the use of therapeutic plasma exchange (TPE) and intralipid therapy.

CASE SUMMARY

An 8-month-old female neutered poodle mix dog ingested an unknown amount of powered bifenthrin, which resulted in acutely altered mentation, cranial nerve deficits, and intractable tremors that persisted in severity despite aggressive medical management to include intravenous fluids, intravenous lipid emulsion, anticonvulsant medications, and methocarbamol. TPE was initiated after lack of significant clinical improvement 12 hours after initial presentation. The dog underwent cardiopulmonary arrest (CPA) following approximately 1 plasma volume equivalent exchange. The dog was successfully resuscitated and showed marked improvement 12 hours postarrest and post-TPE treatment. Serum bifenthrin concentrations were analyzed prior to TPE (445.38 ng/mL) and ∼10 hours after TPE (51.18 ng/mL), which resulted in an 89% reduction in serum bifenthrin concentration.

NEW INFORMATION

TPE may be a promising adjunctive therapeutic modality for bifenthrin toxicosis in dogs.

Toxicokinetic of cyphenothrin in rabbits

Type II pyrethroids, including cyphenothrin, have a wider efficacy and spectrum of action because they have a killing effect rather than a knockdown effect on pests. For this reason, they are among the most widely used pyrethroid groups today. In addition, this group also has repellent activity. Thus, cyphenothrin is a commonly used pyrethroid, which poses an exposure/toxicity risk for living organisms. Toxicokinetic studies have an important place in predicting the toxicity risks of compounds and evaluating viable treatment options. In this study, the toxicokinetics of cyphenothrin were investigated in rabbits. The animal material of the study comprised 6-month-old female 14 New Zealand rabbits, each weighing 2-2.5 kg. The animals were randomly assigned to two groups, each of 7 animals. The rabbits in group 1 were administered a single dose of 2.5 mg/kg bw cyphenothrin in dimethyl sulfoxide as an intravenous bolus, while the rabbits in group 2 were administered a single dose of 2.5 mg/kg bw cyphenothrin in the same vehicle as an oral bolus. Following the administration of cyphenothrin, blood samples were taken at certain intervals from the auricular vein into heparinized tubes. Plasma cyphenothrin levels were determined by gas chromatography, using a capillary column and a micro-electron capture detector. For orally administered cyphenothrin, the plasma maximum concentration (Cmax), time to reach the maximum value (tmax), half-life (t1/2β), mean residence time (MRT), area under the curve (AUC0→∞), and bioavailability (F) values were determined as 172.28 ± 47.30 ng/ml, 1.07 ± 0.42 h, 12.95 ± 1.11 h, 17.79 ± 1.69 h, 2220.07 ± 572.02 ng/h/ml, and 29.50%, respectively. For intravenous cyphenothrin, the t1/2β, MRT and AUC0→∞ values were ascertained as 7.66 ± 0.74 h, 9.28 ± 0.62 h, and 7524.31 ± 2988.44 ng/h/ml, respectively. Although the bioavailability of cyphenothrin was limited when taken orally, its half-life and mean residence time in the body were found to be long. This suggests that high doses of this pesticide may pose a poisoning risk.

Relationship Between the Dose Administered, Target Tissue Dose, and Toxicity Level After Acute Oral Exposure to Bifenthrin and Tefluthrin in Young Adult Rats

Most pyrethroid insecticides (PYRs) share a similar primary target site in mammals. However, the potency estimates of the lethal and sublethal effects of these compounds differ up to 103-fold. The aim of this study was to evaluate the relationship between the dose administered, the target tissue dose, and the effect of 2 highly toxic PYRs, tefluthrin (TEF; 0.1-9 mg/kg) and bifenthrin (BIF; 0.5-12 mg/kg), by using the oral route, a corn oil vehicle (1 ml/kg) and subcutaneous temperature (Tsc) monitoring assays in adult rats. The Tsc was determined at 30-min intervals for 5 h (TEF) or 4.5 h (BIF) after dosing. Rats were sacrificed at 6 h after dosing, and BIF and TEF concentrations were determined in blood (Bd), liver (Lv), and cerebellum (Cb) by using a GC-ECD system. The minimal effective dose of BIF (3 mg/kg) affecting Tsc was similar to that found in prior studies using other testing paradigms. Regarding TEF, a very steep relationship between the dose administered and toxicity was observed, with a near-threshold to low-effective range for Tsc at 0.1-6 mg/kg, and a near lethal syndrome at ≥ 7.5 mg/kg. At 6-7.5 mg/kg TEF, the Cb/Bd and Cb/Lv concentration ratios were both > 1. Conversely, for BIF, the Cb concentration was barely over the Bd concentration and the Cb/Lv concentration ratio remained < 1. Our results and previous findings call for more comprehensive consideration to establish the relevance of the distribution into target tissues and the tissue dosimetry for health risks through the exposure to PYRs in humans.

Determination of offspring NOAEL for zeta-cypermethrin using internal exposure data from rat developmental neurotoxicity studies

Developmental neurotoxicity (DNT) studies via dietary method of administration have been conducted for zeta-cypermethrin, a pyrethroid insecticide. The objectives of the current study were to determine the toxicokinetics (TK) of zeta-cypermethrin in postnatal day (PND) 11, 21 and 90 rats after gavage doses and use the internal exposure data from the DNT and TK studies to calculate an offspring NOAEL in mg/kg/day during lactation. The DNT studies showed that zeta-cypermethrin is not a developmental neurotoxicant. The NOAEL for maternal and offspring was determined to be 125 ppm (9.0 and 21.4 mg/kg/day for dams during gestation and lactation, respectively), based on systemic toxicity of reductions in maternal body weight, body weight gains and food consumption and offspring body weight at 300 ppm (LOAEL). The TK data from the gavage study showed that dose normalized C_max and AUC is approximately 3-fold and 2-fold higher in PND 11 and 21 than those in PND 90 rats. By using the mean maternal/offspring plasma concentrations (535/245 ng/mL) during lactation day LD/PND 5-21 from the range-finding DNT studies, a conservative 3.1X relative TK factor (exposure ratio from the gavage study) and equation 3.1 × 535/21.4 = 245/x, the offspring NOAEL of 125 ppm was calculated to be 3.2 mg/kg/day during lactation. The offspring NOAEL based on internal exposure data from DNT studies and TK data after gavage doses is considered conservative for risk assessment for all human populations including infants and children for zeta-cypermethrin.