The optimal dose varies according on the illness, age, parasite status, and, if present, any first-dose allergies. There are 150mcg and 200mcg dosages of ivermectin available. Adults between the ages of 18 and 64 and children between the ages of 0 and 17 are advised to take 20mcg in a single dose as prescribed by a doctor for intestinal parasite infection. It is necessary to take 150mcg in a single dose for infections of the skin or eyes. Only children who weigh more than or equal to 33 pounds are eligible for the dosage (15kgs). For children who weigh less than that, it is not suggested. Additionally, because to their slow metabolism, older adults over the age of 65 should avoid it.