Imipenem is combined with cilastatin to
**Core Concept**
Imipenem is a carbapenem antibiotic that is susceptible to renal dehydropeptidase I (DHP I) enzyme degradation. This enzyme is present in the renal tubules and can cause inactivation of imipenem, leading to reduced efficacy and increased toxicity.
**Why the Correct Answer is Right**
Imipenem is combined with cilastatin to inhibit the action of DHP I enzyme in the renal tubules. Cilastatin is a potent inhibitor of DHP I, which prevents the breakdown of imipenem by this enzyme. This combination allows imipenem to be excreted by the kidneys in its active form, maintaining its efficacy and reducing the risk of toxicity. By inhibiting DHP I, cilastatin effectively prolongs the half-life of imipenem and enhances its antibacterial activity.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is not relevant to the combination of imipenem and cilastatin.
* **Option B:** Cilastatin is not a beta-lactamase inhibitor; it specifically inhibits DHP I enzyme.
* **Option D:** Cilastatin does not have a direct antibacterial effect on its own; its role is to protect imipenem from degradation.
**Clinical Pearl / High-Yield Fact**
When prescribing imipenem-cilastatin, it is essential to monitor renal function closely, as the combination can cause nephrotoxicity, particularly in patients with pre-existing renal impairment.
**Correct Answer: C. Inhibit DHP I enzyme in the renal tubules.**