What is the most appropriate initial intervention for a painful fluctuant nodule on the buttock?

The most appropriate initial intervention for a painful fluctuant nodule on the buttock is incision and drainage. This approach is specifically indicated when dealing with an abscess, which is characterized by a localized collection of pus resulting from infection. The presence of pain and fluctuation suggests that the nodule is indeed an abscess that requires evacuation of the infected fluid to provide relief to the patient.

Incision and drainage not only alleviates pain but also facilitates the resolution of the infection by physically removing the purulent material. After the procedure, appropriate culture of the drained material can guide further management, including antibiotic therapy if necessary.

While options such as topical mupirocin ointment or systemic antibiotics might be considered in cases of superficial skin infections or to aid healing, they would not address the immediate need for drainage in a fluctuant abscess. Furthermore, moist compresses may help with comfort or to promote drainage in less severe or non-fluctuant cases, but they do not suffice as a definitive treatment for an abscess that warrants incision and drainage. Therefore, incision and drainage is deemed the most suitable initial intervention for this condition.