What agent is added to imipenem to increase its half-life?

The agent added to imipenem to increase its half-life is cilastatin. Imipenem is a broad-spectrum carbapenem antibiotic that is rapidly metabolized by renal enzymes, specifically dehydropeptidase I, which can lead to the production of toxic metabolites. Cilastatin acts as a dehydropeptidase inhibitor, preventing the breakdown of imipenem in the kidneys and allowing for higher and more sustained plasma levels of the antibiotic. By co-administering cilastatin with imipenem, the therapeutic effects are maximized, leading to a longer duration of action and reducing the potential for toxicity associated with its metabolites.

Other options do not serve this specific purpose. Meropenem is another carbapenem antibiotic but does not require cilastatin for its metabolism, as it is not affected by dehydropeptidase I. Vancomycin is an antibiotic used for gram-positive infections and does not relate to increasing the half-life of imipenem. Probenecid is generally used to prolong the effects of penicillins by inhibiting renal excretion but is not utilized in the same way with imipenem, making cilastatin the correct choice for this question.