Abnormal vitamin K metabolism in the presence of normal clotting factor activity in factory workers exposed to 4-hydroxycoumarins. (49/71)

The case histories of two patients exposed to the novel anticoagulants brodifacoum and difenacoum are reported. Abnormal vitamin K1 metabolism, as indicated by elevated vitamin K1 2,3-epoxide plasma concentrations after i.v. administration of vitamin K1, could be detected for more than 18 months after exposure to the anticoagulants. There was a marked prolongation of prothrombin time (greater than 50 s) in both cases, at the time of exposure. However, subsequent haematological investigations (prothrombin time and vitamin K-dependent clotting factor activity) have been shown to be normal in both cases for at least 18 months. These cases confirm the long-acting nature of brodifacoum and difenacoum and present an apparent dissociation between the effect of coumarin anticoagulants on vitamin K1 metabolism and clotting factor activity.  (+info)

A study of the relationship between the pharmacokinetics and the pharmacodynamics of the 4-hydroxycoumarin anticoagulants warfarin, difenacoum and brodifacoum in the rabbit. (50/71)

The pharmacokinetics and pharmacodynamics of the 4-hydroxycoumarin anticoagulants, brodifacoum, difenacoum, and warfarin have been studied in the rabbit. Sensitive (50 ng ml-1) and specific high performance liquid chromatography assays have been developed for the determination of plasma concentrations of warfarin, brodifacoum and difenacoum. After administration of a single intravenous dose (20 mumol kg-1), plasma concentrations of warfarin underwent mono-exponential decay, with a terminal half-life of 5.6 +/- 0.7 h (mean +/- s.e. mean), whereas plasma concentrations of brodifacoum and difenacoum underwent bi-exponential decay with terminal half-lives of 60.8 +/- 1.9 h and 83.1 +/- 10.3 h respectively. The plasma half-life of brodifacoum in a single patient poisoned with the compound was 487 h. The pharmacological response to the anticoagulants was measured as changes in prothrombin complex activity, from which the rate of clotting factor synthesis was determined. Clotting factor synthesis recovered in a monophasic fashion after a single intravenous dose of warfarin, compared with a more complex biphasic, pattern of recovery of clotting factor synthesis after administration of either brodifacoum or difenacoum. The slope (m) of the intensity of effect-log (amount of drug in the body) curve was derived for each anticoagulant. There was no significant difference in the value of m after single intravenous doses of racemic, R-, and S-warfarin, difenacoum and brodifacoum, which is consistent with the hypothesis that all the 4-hydroxycoumarin anticoagulants produce their anticoagulant effect by acting at the same receptor site, vitamin K epoxide reductase. Determination of the minimum plasma concentration of each anticoagulant that corresponded with the complete inhibition of clotting factor synthesis indicated that racemic warfarin, R-warfarin and brodifacoum have similar potencies in the rabbit and are less potent than S-warfarin and difenacoum.  (+info)

Evaluation of coumatetralyl against two predominant murid species. (51/71)

Coumatetralyl was evaluated in the laboratory against Bandicota bengalensis and Rattus rattus. Feeding tests with 0.0375% coumatetralyl baits produced 100% mortality after a single day feeding period in B. bengalensis and after a 10-day period in R. rattus. The anticoagulant bait is less palatable in comparison to plain bait. In the case of R. rattus, LFP50 and LFP98 and their 95% confidence limits were 3.89 (2.62-5.77) days and 11.22 (6.1-20.65) days respectively. Median period of survival and its 95% confidence limits of B. bengalensis and R. rattus were 4.7 (3.85-5.7) days and 11.2 (9.33-13.44) days respectively.  (+info)

Laboratory test of seven rodenticides for the control of Mastomys natalensis. (52/71)

Laboratory feeding tests were carried out to assess the efficacy of seven rodenticides against Mastomys natalensis. The poisons (warfarin, coumatetralyl, difenacoum, brodifacoum, bromadiolone, calciferol and zinc phosphide) were all toxic at the concentrations normally used against Rattus norvegicus (Berk.), although several were unpalatable. Trials are now needed to demonstrate the relative efficacy of these poisons in the field, but it is likely that, given suitable bait formulations, they would all be useful as practical control agents.  (+info)

Field trials of WBA 8119 (PP 581, brodifacoum) against warfarin-resistant infestations of Rattus norvegicus. (53/71)

Baiting with medium oatmeal or soaked wheat containing 0.002, 0.001 or 0.0005% brodifacoum completely controlled infestations of warfarin-resistant rats on farms when the poisoned baits were maintained until rats ceased to feed on them. The concentration of brodifacoum did not affect the duration of these treatments which lasted from 11 to 25 days. Poison baiting with 0.002% brodifacoum for only 1,4 and 7 days achieved, respectively, only about 41, 51 and 68% control of similar farm infestations, and so emphasized the need to continue baiting for longer periods.  (+info)

Laboratory trials of five rodenticides for the control of Mesocricetus auratus Waterhouse. (54/71)

The efficacy of five rodenticides for use in bait against the golden hamster (Mesocricetus auratus Waterhouse) was investigated in the laboratory. The species proved to be resistant to warfarin (up to 0.5%) and difenacoum (0.005%), but brodifacoum (0.005%) gave complete mortality after three days' feeding. Calciferol (0.1%), though toxic, was significantly unpalatable. Zinc phosphide (5.0%) presented in a choice test for two days against unpoisoned feed gave 100% mortality, and appears to be the most suitable of these compounds for the control of M. auratus in the field.  (+info)

Oral anticoagulation in the treatment of a spontaneously metastasising murine tumour (3LL). (55/71)

The effects of long-term anticoagulation with phenprocoumon on growth of the Lewis lung carcinoma (3LL) were studied. Oral anticoagulation initiated at the day of i.m. transplantation of the 3LL into C57BL mice significantly inhibited primary tumour growth and reduced the number of spontaneous metastases to the lungs. Intermittent anticoagulation was without effect on metastasis formation but still retarded primary growth. There was no influence of anticoagulation on the mean survival time (MST) of tumour-bearing animals. Phenprocoumon appears to improve the results of cyclophosphamide of 5-fluorouracil treatment, but there were no statisticially significant differences. In contrast, bleomycin treatment in combination with adjuvant anticoagulation suggested a possible drug synergy. No significant influence of anticoagulation on the response of the primary tumour to irradiattion was found, though the MST of irradiated and anticoagulated animals was greater than in the solely irradiated controls. The present investigations suggest that coumarin derivatives have some direct tumour-inhibiting capacities, but exert their antimetastatic action via deceleration of the blood clotting mechanism.  (+info)

The susceptibility of Bandicota bengalensis from Rangoon, Burma to several anticoagulant rodenticides. (56/71)

The baseline susceptibility of the lesser bandicoot rat, Bandicota bengalensis, from Rangoon, Burma, to five anticoagulant rodenticides was established with no-choice feeding in the laboratory. The susceptibility of lesser bandicoots to the several poisons (brodifacoum, difenacoum, diphacinone, coumatetralyl, and warfarin) was such that they were offered at a 0.001% concentration. B. bengalensis was most susceptible to brodifacoum, and in descending order, difenacoum, coumatetralyl, diphacinone and warfarin. In comparison with Rattus norvegicus on warfarin at 0.005%, B. bengalensis proved more susceptible. Feeding tests at 0.005% concentration indicated that a 1-day feeding on brodifacoum and difenacoum would result in complete mortality, whereas coumatetralyl and warfarin would require 4 days feeding to a 100% kill. Brodifacoum and difenacoum are recommended at 0.002-0.005% bait concentrations and coumatetralyl at 0.005--0.01% concentrations for the control of B. bengalensis in the field in Rangoon. The use of any anticoagulant material in rat control should be alternated with acute toxicants to retard the possible development of anticoagulant resistance.  (+info)