## **Core Concept**
The patient's presentation of copious vaginal discharge is suggestive of a sexually transmitted infection (STI), specifically bacterial vaginosis or trichomoniasis, given her sexually active status and symptoms. Syndromal management of vaginal discharge involves treating symptoms based on a set of clinical criteria rather than waiting for laboratory confirmation.

## **Why the Correct Answer is Right**
The correct approach in syndromal management for a patient presenting with vaginal discharge, particularly when it is copious and the patient is sexually active, often involves treating for the most likely causes: bacterial vaginosis (BV), trichomoniasis, and gonorrhea/chlamydia, although the discharge characteristics can help differentiate. For BV and trichomoniasis, **metronidazole** or **tinidazole** are first-line treatments. Given that option **C** includes **metronidazole**, this is an appropriate choice for treating BV and trichomoniasis, which are common causes of vaginal discharge in sexually active women.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is not provided, but typically, incorrect options might include treatments not indicated for the likely causes of vaginal discharge in this context, such as antiviral medications or treatments for yeast infections.
- **Option B:** Without specifics, if this option does not include **metronidazole** or an appropriate alternative like **tinidazole**, it would be incorrect because these are the recommended treatments for BV and trichomoniasis.
- **Option D:** Similarly, if this option does not align with recommended treatments for the likely diagnoses, it would be incorrect.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that in syndromal management of vaginal discharge, **metronidazole** (or **tinidazole**) is a cornerstone treatment for bacterial vaginosis and trichomoniasis. For women with uncomplicated gonorrhea or chlamydia, **ceftriaxone** (for gonorrhea) and **azithromycin** or **doxycycline** (for chlamydia) are recommended. The presence of copious discharge often points towards BV or trichomoniasis.

## **Correct Answer:** C. Metronidazole.