Stromectol (ivermectin) has been approved as a treatment for infection with nondisseminated intestinal threadworm (strongyloidiasis). Stromectol is a very effective anti-parasitic medicine which often cures intestinal (i.e., nondisseminated) strongyloidiasis, an infection caused by the threadworm Strongyloides stercoralis, with a single oral dose.

The recommended dose of Stromectol for the treatment of intestinal (i.e., nondisseminated) strongyloidiasis is a single oral dose, based on weight (200 micrograms of Stromectol per kilogram of body weight). In clinical trials, the most common adult dose used was two 6 mg tablets, which is recommended for people weighting 51-65 kg (112-143). Stromectol can also be used in children who weigh 15 kg (33 lb.) or more, at a dose ranging from 1/2 to 2 tablets; again, the dosage is based on weight. After treatment, at least three stool examinations should be conducted over the three months following treatment to ensure eradication.

Stromectol has also been cleared by the U.S. Food and Drug Administration to treat onchocerciasis, or river blindness. The recommended dose of Stromectol for the treatment of onchocerciasis is a single oral dose based on weight (150 micrograms per kilogram of body weight). Stromectol is available under the name Mectizanr in many regions of the world including Africa, Central and South America, the Middle East and others. Onchocerciasis occurs very rarely in the U.S.

Stromectol does not kill the adult Onchocerca parasites, and therefore repeated follow-up and retreatment is usually required. For the treatment of individual patients, retreatment may be considered at intervals as short as 3 months. Surgical removal of nodules containing adult Onchocerca parasites may be considered in the management of patients with onchocerciasis, since this procedure will eliminate the adult parasite.

Merck’s catalog price for Stromectol is $7.50 per tablet, or approximately $15 for an average single dose.

Most of the 200 patients treated with Stromectol (64 to 100 percent in five clinical trials) had their intestinal threadworm infection eradicated after one dose. In these trials, Stromectol was generally well tolerated.

In clinical trials on Strongyloidiasis, the following adverse experiences occurred in greater than 1 percent of the patients: diarrhea (1.8 percent), nausea (1.8 percent), dizziness (2.8 percent) and pruritus (itching) (2.8 percent).

Patients treated with Stromectol for onchocerciasis may experience allergic and inflammatory responses to the death of microfilariae. These adverse events may include arthralgia/synovitis (9.3 percent), axillary lymph node enlargement and tenderness (11.0 and 4.4. percent, respectively), inguinal lymph node enlargement and tenderness (12.6 percent and 13.9 percent, respectively), other lymph node enlargement and tenderness (3.0 percent and 1.9 percent, respectively), pruritus (27.5 percent), skin involvement including edema, papular and pustular or frankurticarial rash (22.7 percent) and fever (22.6 percent).

Up to four percent of the population in some parts of the United States are infected with intestinal threadworm, although the vast majority remain asymptomatic and undiagnosed. Symptoms include gastric pain and tenderness, vomiting and diarrhea. Infection with intestinal threadworm most often is caused when the threadworm penetrates the skin of the feet through contaminated soil or through eating contaminated food. Infection with threadworm is most common in tropical climates and unsanitary living conditions.