## **Core Concept**
Cilastatin is used in combination with imipenem to inhibit the renal enzyme dehydropeptidase-1 (DHP-1). Imipenem is a carbapenem antibiotic that is effective against a broad spectrum of bacteria. However, it is prone to degradation by DHP-1.

## **Why the Correct Answer is Right**
Imipenem is a potent antibiotic but is rapidly hydrolyzed by dehydropeptidase-1 (DHP-1) in the renal tubules. This degradation leads to a reduction in its antibacterial efficacy. Cilastatin, a specific inhibitor of DHP-1, is given in combination with imipenem to prevent its degradation. By inhibiting DHP-1, cilastatin ensures that imipenem reaches the urinary tract in its active form, thereby maintaining its therapeutic efficacy.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because while cilastatin does have effects on renal function, its primary purpose in combination with imipenem is not related to increasing renal blood flow or affecting creatinine clearance directly.
- **Option B:** This option is incorrect because cilastatin does not act as a beta-lactamase inhibitor. Beta-lactamase inhibitors, like clavulanic acid, are used to protect penicillins from degradation by beta-lactamases, not to protect carbapenems like imipenem from DHP-1.
- **Option C:** This option might seem plausible but is incorrect because the primary concern with imipenem alone is its degradation by DHP-1, not its nephrotoxicity. While nephrotoxicity is a concern with some antibiotics, cilastatin's role is specifically to prevent imipenem's degradation.
- **Option D:** This option is incorrect because there is no established benefit of cilastatin in reducing the gastrointestinal side effects of imipenem.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the combination of imipenem and cilastatin (marketed as Primaxin) is used to treat severe infections, particularly those caused by multi-drug resistant bacteria. The addition of cilastatin allows for higher concentrations of imipenem to be achieved in the urine and tissues, enhancing its therapeutic effectiveness.

## **Correct Answer:** C. To inhibit dehydropeptidase enzyme.