Brodifacoum (talontm Rodenticide), a Novel Concept

Brodifacoum, a new rodenticide, is described. This anticoagulant is shown to be of exceptional potency and capable of controlling resistant rodents as well as several non-commensal species. Results demonstrate that, in contrast to first generation anticoagulants, a bait concentration of only 50 ppm is adequate to give control and in only a single feeding for most species. In common with other anticoagulants, vitamin K1 is an effective antidote. In contrast with other acute rodenticides, symptoms are delayed and no bait shyness is observed. The results of laboratory and field trials from many parts of the world are summarized and comparisons of efficacy and specificity with other rodenticides are made. In all cases, brodifacoum is shown to be an exceptional rodenticide, the single feeding action of which offers novel rodent control applications. The discovery of warfarin (Link, 1945) and exploitation of anticoagulants as rodenticides (O'Connors, 1948) dramatically increased the efficacy and safety of rodent control programs. The chronic, antidotable action of warfarin eliminated the hazards of acute baits and the need for prebaiting, as bait shyness was not induced. Very rapidly other anticoagulants were developed as rodenticides. These included coumachlor, introduced in 1951; coumatetralyl, introduced in 1956-1957; diphacinone, first described in 1952; and pindone, in the 1940's (Martin and Worthing, 1971). For effective control, multiple bait applications were needed of all these rodenticides, and in general they were found about as equally effective as warfarin (Hayes and Gaines, 1959; Bentley and Larthe, 1959; Greaves and Ayres, 1969). By the late 1950's the anticoagulants became the primary means of rodent control worldwide. Resistance was discovered in R. norvegicus in U.K. (Boyle, 1960), Denmark (Lund, 1967), Netherlands (Ophof and Langeveld, 1968), U.S.(Jackson and Kaukeinen, 1972), Germany (Telle, 1972), and France (Grand, 1976). Concern increased when resistance was also found to occur in the house mouse, Mus musculus (Rowe and Redfern, 1965; Anon., 1977), and the roof rat, R. rattus (Greaves, Rennison and Redfern, 1973; Anon., 1977). Cross resistance to other first generation anticoagulants has also been reported (Rowe and Redfern, 1968; Greaves and Ayres, 1969; Hadler and Shadbolt, 1975; Kosmin and Barlow, n.d.). The difficulty of controlling resistant infestations of R. norvegicus in Europe was eased considerably by the development of difenacoum (Redfern, Gill and Hadler, 1976); results against R. rattus and M. musculus were less favorable (Handler, Redfern and Rowe, 1975) but difenacoum was still recommended by the Pest Infestation Control Laboratory (U.K.) as the best anticoagulant available for the control of resistant house mouse (PICL, 1976). Difenacoum has been commercially available in the UK and elsewhere for a few years, and partially as a result, the spread of warfarin resistance in the UK is no longer formally monitored. In the U.S., no anticoagulant is currently labeled for effective control of resistant rats or mice. Greater than 5% resistant Norway rats have been found in 37% of 73 sampled U.S. urban areas (Anon., 1977). In suspected areas of the U.S. 6/10 Rattus rattus infestations and 7/7 Mus musculus infestations were confirmed to be resistant (Anon., 1977). In certain areas, for example, Chicago and Sioux City, resistance has caused serious control problems (Jackson et al., 1975). The anticoagulant described in this paper, brodifacoum, is a new development. Brodifacoum will be marketed worldwide and in the U.S. for commensal rodents as TALON rodenticide. GENERAL PROPERTIES Brodifacoum (C31H2303BR) is a draft ISO common name for the compound with structure so labeled in Figure 1. The proper chemical name is 3-(3-(4'-bromo(l-l'biphenyl)-4-yl-l,2,3,4-tetra-hydro-lnaphthalenyl)-4-hydroxy -2H-l-benzopyran-2-one. It is also denoted by the code number WBA 8119 and as PP581 or ICI 581, BFC. Figure 1. Structural Formula of brodifacoum.