Methemoglobinemia is a contraindication for which of the following local anesthetics?

Methemoglobinemia is a condition characterized by an elevated level of methemoglobin in the blood, which is a form of hemoglobin that cannot effectively carry oxygen. Prilocaine is associated with this condition because it has a known risk of causing methemoglobinemia, particularly in cases of overdose or in certain individuals who may have specific genetic predispositions.

When prilocaine is metabolized in the body, it can convert hemoglobin into methemoglobin. This is particularly concerning in patients with pre-existing conditions, infants, or those with certain enzyme deficiencies, as they may be more susceptible to this adverse effect.

In contrast, the other local anesthetics listed—mepivacaine, procaine, and septocaine—do not carry the same risk for inducing methemoglobinemia to such an extent that would contraindicate their use in patients with this condition. Therefore, prilocaine is the local anesthetic contraindicated in patients with methemoglobinemia due to its potential to exacerbate this condition.