Toxic baits contain active ingredients that work as either an anticoagulant, causing death by internal bleeding or as a direct toxin (Table 2).

It is important to note that some of the baits on the market may only be used in and around buildings and are not registered for use in the garden and landscape. These include the newer, single-feeding anticoagulants (brodifacoum, bromadiolone, and difethialone) and two of the nonanticoagulants (bromethalin and cholecalciferol). The multiple-feeding anticoagulant baits and zinc phosphide may be used both in and around structures as well as in gardens and landscapes.

Anticoagulant Baits. Anticoagulant baits used to be thought of as relatively safe baits to use around the house and garden because they required multiple feedings to be effective. Newer anticoagulant baits, however, have been developed that only require a single feeding to be effective and are, therefore, more hazardous than the older type of anticoagulant bait to pets and children. Baits that require multiple feedings over a period of several days contain warfarin, chlorophacinone, or diphacinone as their active ingredient, whereas the single-feeding anticoagulants contain brodifacoum, bromadiolone, or difethialone. Whether a bait actually requires multiple feedings or not depends on how much is consumed at each feeding—even the newer, single-feeding baits must be consumed in adequate amounts to be effective. With all anticoagulants, death is generally delayed 2 to 6 days after a lethal dose of bait has been consumed. While both types of anticoagulant toxicants are effective against Norway and roof rats when formulated in acceptable baits, roof rats tend to need a few more feedings to obtain a lethal dose than Norway rats do. This is particularly true with the multiple-feeding anticoagulants, as compared to the single-feeding ones.

Anticoagulant baits are available in meal, pellet, kernel, or block form. Pelleted or meal baits are frequently sold in small packets called "place packs." Also, a wide variety of paraffin block baits are marketed and convenient to use. Most of these blocks must be placed in a tamper-resistant bait station to prevent dogs and other animals from chewing on them.

Nonanticoagulant Baits. Nonanticoagulant baits are usually lethal after one feeding if the rat ingested an adequate amount of toxin. Bromethalin, cholecalciferol, and zinc phosphide are common active ingredients in this group of baits used for rats. These baits are placed in runways or next to burrows where rats will find them. Nonanticoagulant baits are generally more rapid acting than anticoagulant baits and you may find dead rodents within 12 hours of baiting. Because the toxins in these baits do not accumulate in the tissue of the rodent, predators or scavengers such as dogs and cats are not likely to be adversely affected by eating poisoned carcasses (see sidebar, Pets and Rat Control). However, they, as well as other animals and children, can be affected by eating the bait so it must be stored and used carefully.