Piperazine is rapidly absorbed from the GI tract, and piperazine base can be detected in the urine as early as 30 min after administration. The excretion rate is maximal at 1–8 hr, and excretion is practically complete within 24 hr. The spectrum of activity of piperazine is largely against ascarid parasites in all animal species (including people). The safety margin is wide.
Diethylcarbamazine (DEC), a derivative of piperazine, also acts to paralyze nematodes by interfering with nerve function. Historically, DEC was widely used for heartworm prevention in dogs. It was given daily PO throughout the mosquito season to prevent patent infections. Before DEC use, dogs must first be cleared of adult heartworms and microfilariae to avoid an often fatal reaction. DEC has also been used to treat prepatent Dictyocaulus viviparus infections (see Lungworm Infection) in cattle, although it is relatively ineffective against the adult worms. It is routinely given IM at 22 mg/kg body wt for 3 consecutive days, although it is reported that one injection at 44 mg/kg provides better relief of clinical signs.
Clorsulon is a sulfonamide given PO as a suspension for infections with (mainly) adult liver flukes in sheep and cattle and as a SC injection for cattle, in combination with ivermectin. In plasma, clorsulon is bound to protein and, when ingested by liver flukes, inhibits enzymes of the glycolytic pathway. Clorsulon has a wide safety margin and is licensed for use in some countries (eg, Australia, Europe) in lactating dairy cows producing milk for human consumption. It is not licensed in the USA.
Bunamidine is an anticestodal compound. It is used in small animals and is most effective if given after fasting. It is absorbed and metabolized in the liver and leads to digestion of tapeworms in the gut of the host. Vomiting and mild diarrhea may be seen, and exercise or excitement should be avoided in dogs soon after administration.
Nitroscanate, like the substituted phenols, probably acts by uncoupling oxidative phosphorylation. It is used in small animals against Toxocara, Toxascaris, Taenia, Dipylidium, Ancylostoma, Uncinaria, and Echinococcus spp. Vomiting occasionally occurs after treatment.
A number of organophosphates have been used as anthelmintics; however, because of their relative toxicity, limited efficacy against immature stages, narrow margin of safety, and contamination of the environment through fecal excretion, their use has declined. Dichlorvos is used as an anthelmintic in horses, pigs, dogs, and cats; trichlorfon in horses against bots, ascarids, and oxyurids; and coumaphos, crufomate, haloxon, and naphthalophos in ruminants. Because of its high volatility, dichlorvos is a particularly versatile organophosphate that can be incorporated as a plasticizer in vinyl resin pellets; it is released slowly from the inert pellets as they pass through the GI tract, providing a therapeutic concentration along the tract. Dichlorvos is particularly useful in pigs against all major adult nematodes and was one of the first broad-spectrum anthelmintics to be used in this species. There is little or no activity against larval migrating nematodes.