A 16-year-old with weight loss, polyuria, polydipsia, and positive pancreatic autoantibodies arrives with blood glucose 420 mg/dL and ketonuria. Which is the immediate appropriate management and rationale?

Start an SGLT2 inhibitor immediately because they are the safest agents in patients with ketonuria and eliminate the need for insulin in type 1 diabetes.

Urgent initiation of intravenous insulin and fluid resuscitation because this presentation indicates type 1 diabetes with ketoacidosis risk requiring insulin to suppress ketogenesis and correct hyperglycemia.

Advise high-carbohydrate diet to combat weight loss and postpone pharmacotherapy as the condition will self-correct in weeks without intervention.

Begin metformin and schedule outpatient follow-up because oral agents are first-line for all adolescents with hyperglycemia including those with ketosis.