**Core Concept**
Cilastatin is a dehydropeptidase inhibitor that is co-administered with Imipenem, a carbapenem antibiotic, to prevent its degradation in the kidneys. This combination is essential to maintain the efficacy of Imipenem.

**Why the Correct Answer is Right**
Imipenem is a carbapenem antibiotic that is susceptible to renal dehydropeptidase degradation. Cilastatin inhibits this enzyme, thereby preventing the breakdown of Imipenem in the kidneys. This allows Imipenem to be excreted in its active form, thereby maintaining its efficacy. The combination of Cilastatin and Imipenem is a classic example of pharmacokinetic enhancement, where the co-administration of a second drug (Cilastatin) improves the pharmacokinetics of the primary drug (Imipenem).

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because Cilastatin does not enhance the antibacterial activity of Imipenem. Instead, it prevents its degradation.
**Option B:** This option is incorrect because Cilastatin does not have any direct effect on the renal excretion of Imipenem. Its primary role is to inhibit the dehydropeptidase enzyme.
**Option C:** This option is incorrect because Cilastatin does not have any significant effect on the absorption of Imipenem. The combination is primarily used to prevent renal degradation of Imipenem.

**Clinical Pearl / High-Yield Fact**
When co-administering Cilastatin with Imipenem, it is essential to note that the combination is not indicated for patients with renal impairment, as the dehydropeptidase enzyme is already inhibited in these patients.

**Correct Answer:** C. Cilastatin inhibits the renal dehydropeptidase enzyme that breaks down Imipenem.