The correct answer is Prilocaine.

- Prilocaine is a local anesthetic agent known to have a higher risk of causing methemoglobinemia compared to other anesthetics.
- Methemoglobinemia is a condition where the iron in hemoglobin is oxidized from the ferrous (Fe²⁺) to the ferric (Fe³⁺) state, resulting in decreased oxygen delivery to tissues.
- This can be especially dangerous in patients with congenital or acquired methemoglobinemia, as their ability to reduce methemoglobin back to hemoglobin is already compromised.

- The metabolism of prilocaine produces an oxidative metabolite called o-toluidine, which is a potent inducer of methemoglobin formation.
- For this reason, prilocaine should be avoided or used with extreme caution in patients with a history of or underlying conditions predisposing to methemoglobinemia.

Other local anesthetics such as lidocaine, bupivacaine, and mepivacaine have lower potential for inducing methemoglobinemia and are generally considered safer in these patients.

Key Points:
- Prilocaine metabolism generates o-toluidine, an oxidizing agent that increases methemoglobin levels.
- Patients with congenital or acquired methemoglobinemia have a decreased capacity to reduce methemoglobin.
- Use of prilocaine in such patients can exacerbate hypoxia and lead to serious complications.
- Other local anesthetics like lidocaine, bupivacaine, and mepivacaine are preferred alternatives.

Reference: Goodman & Gilman's The Pharmacological Basis of Therapeutics, 13th Edition, Volume 1, Chapter 27 / Page 700