Side effects may include abdominal pain, vomiting, headache, and dizziness.[2] Use is not recommended during
breastfeeding or the
third trimester of
pregnancy.[2] Serious side effects may include an increased risk of infection.[3] It belongs to the
anthelmintic class of medications.[3]
Levamisole was originally used as an
anthelmintic to treat worm infestations in both humans and animals. Levamisole works as a
nicotinic acetylcholine receptoragonist that causes continued stimulation of the parasitic worm muscles, leading to paralysis.[8] Levamisole has gained prominence among
aquarists as an effective treatment for Camallanusroundworm infestations in
freshwatertropical fish.[9] Levamisole has been used to treat small ruminant animals since the late 1960s.[10] Levamisole-resistant parasitic worms are common in sheep farms in New Zealand,[11] Uruguay,[12] Paraguay,[13] and Brazil.[14]
An interesting side effect these reviewers reported in passing was "neurologic excitement". Later papers, from the Janssen group and others, indicate levamisole and its enantiomer, dexamisole, have some mood-elevating or
antidepressant properties, although this was never a marketed use of the drug.[16][17]
Adverse effects
One of the more serious side effects of levamisole is
agranulocytosis, or the depletion of the white blood cells. In particular, neutrophils appear to be affected the most. This occurs in 0.08–5% of the studied populations.[18]
Levamisole is readily absorbed from the gastrointestinal tract and metabolized in the liver. Its time to peak plasma concentration is 1.5–2 hours. The plasma elimination half-life is fairly quick at 3–4 hours which can contribute to not detecting levamisole intoxication. The metabolite half-life is 16 hours. Levamisole's excretion is primarily through the kidneys, with about 70% being excreted over 3 days. Only about 5% is excreted as unchanged levamisole.[22][23]
Drug testing of racehorse urine has led to the revelation that among levamisole equine metabolites are both
pemoline and
aminorex, stimulants that are forbidden by racing authorities.[24][25][26] Further testing confirmed aminorex in human and canine urine, meaning that both humans and dogs also metabolize levamisole into aminorex,[27] though it is unclear whether plasma aminorex is present at any appreciable level. Blood samples following oral administration of levamisole out to 172 hr post-dose did not demonstrate any plasma aminorex levels above that of the limit of quantification (LoQ). Additionally, in cocaine-positive plasma samples, of which 42% contained levamisole, aminorex was never reported at concentrations higher than LoQ.[28]
Detection in body fluids
Levamisole may be quantified in blood, plasma, or urine as a diagnostic tool in clinical poisoning situations or to aid in the medicolegal investigation of suspicious deaths involving adulterated street drugs. About 3% of an oral dose is eliminated unchanged in the 24-hour urine of humans. A post mortem blood levamisole concentration of 2.2 mg/L was present in a woman who died of a cocaine overdose.[29][30]
Adulterant in illegal drugs
Levamisole has increasingly been used as a
cutting agent in
cocaine sold around the globe with the highest incidence being in the United States. In 2008–2009, levamisole was found in 69% of cocaine samples seized by the
Drug Enforcement Administration (DEA).[19] By April 2011, the DEA reported the adulterant was found in 82% of seizures.[31]
Levamisole adds bulk and weight to powdered
cocaine (whereas other adulterants produce smaller "rocks" of cocaine) and makes the drug appear purer.[32] In a series of investigative articles for The Stranger, Brendan Kiley details other rationales for levamisole's rise as an adulterant: possible stimulant effects, a similar appearance to cocaine, and an ability to pass street purity tests.[33]
Levamisole suppresses the production of
white blood cells, resulting in
neutropenia and
agranulocytosis. With the increasing use of levamisole as an
adulterant, a number of these complications have been reported among cocaine users.[19][34][35] Levamisole has also been linked to a risk of
vasculitis,[36] and two cases of vasculitic skin necrosis have been reported in users of cocaine adulterated with levamisole.[37]
Levamisole-tainted cocaine has caused three deaths and sickened over 100 in US and Canada, as of 2009.[38]
Chemistry
The original synthesis at Janssen Pharmaceutica resulted in the preparation of a
racemic mixture of two
enantiomers, whose hydrochloride salt was reported to have a melting point of 264–265 °C; the free base of the racemate has a melting point of 87–89 °C. The racemic mixture is referred to as "tetramisole" - levamisole refers only to the levorotatory enantiomer of tetramisole.[citation needed]
It is used to immobilize the nematode C. elegans on glass slides for imaging and dissection.[42]
In a C. elegans behavioral assay, analyzing the time course of paralysis provides information about the neuromuscular junction. Levamisole acts as an acetylcholine receptor agonist, which leads to muscle contraction. Continuing activation leads to paralysis. The time course of paralysis provides information about the acetylcholine receptors on the muscle. For example, mutants with fewer acetylcholine receptors may paralyze slower than wild type.[43]
Research
It has been studied as a method to stimulate the immune system as part of the treatment of
cancer.[44] It has also shown some efficacy in the treatment of
nephrotic syndrome in children.[45]
After being pulled from the market in the US and Canada in 1999 and 2003, respectively, levamisole has been tested in combination with
fluorouracil to treat
colon cancer. Evidence from
clinical trials support its addition to fluorouracil therapy to benefit patients with colon cancer. In some of the leukemic cell line studies, both levamisole and
tetramisole showed similar effect.[46]
Veterinary uses
The combination
doramectin/levamisole, sold under the brand name Valcor, is
indicated for the treatment and control of gastrointestinal roundworms, lungworms, grubs, sucking lice, and mange mites in cattle.[6] It is given by
subcutaneous injection.[6]
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