Which medication is administered solely by subcutaneous injection?

Incretin mimetics are a class of medications specifically designed for the management of type 2 diabetes, and they are indeed administered solely by subcutaneous injection. This administration route is essential for these medications because they are peptides, which are proteins consisting of amino acids. Peptides would be broken down and rendered ineffective if taken orally due to the digestive enzymes present in the gastrointestinal tract.

Incretin mimetics, such as exenatide and liraglutide, mimic the action of incretin hormones that increase insulin secretion in response to meals, reduce glucagon release, and slow gastric emptying. This mechanism helps to regulate blood glucose levels effectively. The subcutaneous route ensures that the peptide remains intact and bioavailable, allowing for optimal therapeutic effects.

On the other hand, the other choices relate to oral or different routes of administration. Metformin and acarbose are taken orally, while repaglinide, though taken before meals, does not require injection. Hence, the specific requirement for subcutaneous administration clearly identifies incretin mimetics as the correct answer.