Levamisole is an antiparasitic and immune stimulant that is typically used to eliminate nematodes in livestock such as pigs, cattle and sheep. It can be found in a variety of deworming medications and has been used in horses off-label as an adjunctive medication in the treatment of equine protozoal myeloencephalitis, or EPM.

Equine protozoal myeloencephalitis is a disease of horses that affects the central nervous system; specifically, the brain and/or spinal cord.1 Its primary causative agent is the protozoan organism Sarcocystis neurona. EPM was first described in the 1960s as segmental myelitis, but by the mid-1970s it was determined that the disease was caused by a protozoan organism. S. neurona was first isolated from the spinal cord of a horse with clinical signs of EPM in the early 1990s. In the late 1990s, the protozoan Neospora hughesi was also shown to also cause EPM in horses but, compared to S. neurona, it is a relatively rare cause of this disease.1 EPM is a disease primarily of the Western Hemisphere and is not commonly seen in other parts of the world. 

Levamisole: Controversial Uses 

In horses, levamisole metabolizes to aminorex and possibly pemoline, which are considered potent stimulants assigned a 1/A Classification in the Association of Racing Commissioners International (ARCI) Uniform Classification of Foreign Substances. This has created a difficult scenario for the owners of performance (racing) horses, as its presence creates the look of an intentional aminorex dosage even if levamisole was used only as a dewormer. It is because of this that levamisole itself has become a Class 2 medication, while aminorex is a Class 1 according to the ARCI.3 In consideration of its conventional use in horses, in 2017 the Racing Medication and Testing Consortium (RMTC) contemplated an administration study to develop guidance on the use of levamisole and surveyed practicing veterinarians on their use of this medication.

In recent years, levamisole has widely appeared as a cutting agent in illicit (street) drugs, primarily cocaine and to a lesser extent, heroin. In fact, levamisole-contaminated cocaine has been reported as a growing problem in the United States and other countries, with patients exposed to levamisole-contaminated cocaine having been identified in several US states. In 2009, the US Drug Enforcement Agency (DEA) reported that 69% of the cocaine entering the US contained levamisole. The DEA has also detected trace amounts of levamisole in heroin seizures.4

Where to buy Levamisole 

Levamisole is available in the U.S. through pharmaceutical manufacturers and through veterinary custom compounding companies. 

Levamisole carries several potential drug interactions. Please consult your veterinarian prior to beginning any treatment regimen.

FOR RX ONLY: A valid prescription from a licensed veterinarian is required for dispensing this medication.

1aaep.org.

3pastthewire.com.

4health.ny.gov.