Methylene BlueDose, contraindications and adverse effects for Cats, Dogs and Horses.

Reduces methemoglobin back to functional hemoglobin; the antidote for methemoglobinemia (e.g. from nitrate, acetaminophen, or onion toxicosis). Methylene blue is used primarily in ruminants for treating methemoglobinemia secondary to oxidative agents (eg, nitrates, nitrites, chlorates) and occasionally as an adjunctive or alternative therapy for cyanide toxicity. In dogs, methylene blue may be considered for treating methemoglobinemia secondary to drugs or toxins (eg, phenol, mothballs, hydroxyurea, phenazopyridine). It can also b

Methylene blue is rapidly converted to leucomethylene blue in tissues. This compound serves as a reducing agent that helps to convert methemoglobin (Fe+++) to hemoglobin (Fe++). Methylene blue is an oxidating agent and may actually cause methemoglobinemia if high doses are administered (species-dependent). 860 Methylene Blue Methylene blue also has antimicrobial activity.

Methylene blue is contraindicated in patients with renal insufficiency and in patients that are hypersensitive to it. It cannot be given as an intrathecal injection. Methylene blue is generally considered contraindicated in cats, as it can result in Heinz body anemia and methemoglobinemia. Al- though the number of cells with Heinz bodies increased after two doses of methylene blue, no increase was seen after a single dose.

The greatest concerns with methylene blue therapy are the development of Heinz body anemia or other erythrocyte morphological changes, methemoglobinemia, and decreased erythrocyte life spans. Cats tend to be very sensitive to these effects and it is generally considered contraindicated in feline patients; however, dogs and horses can also develop hematologic adverse effects at relatively low doses.

■ Methemoglobinemia using co-oximetry or multi-wavelength pulse oximetry; pulse oximetry is not reliable ■ Erythrocyte morphology, indices (eg, MCV, MCHC), hematocrit, hemoglobin

A withdrawal interval is stated for this drug. It depends on the formulation, route and dose, so read the exact wording in the interactive drug guide before treating a food animal.