Correct Answer: B. Metronidazole
The clinical triad of vaginal itching, green frothy discharge, and strawberry vagina is pathognomonic for Trichomoniasis vaginalis infection. The strawberry appearance (punctate hemorrhagic spots on the cervix and vaginal mucosa) is a hallmark sign caused by the mechanical trauma from the motile trophozoites. Metronidazole is the gold standard and first-line DOC for trichomoniasis in India, as per IAP and FOGSI guidelines. It is a nitroimidazole that disrupts the DNA of the parasite, leading to its death. The standard regimen is 400 mg orally twice daily for 7 days, or a single 2 g dose. Metronidazole achieves excellent vaginal and urethral concentrations and has a cure rate exceeding 95%. Importantly, both the patient and her sexual partner(s) must be treated simultaneously to prevent reinfection, as trichomoniasis is a sexually transmitted infection. The drug is safe in non-pregnant women; however, in pregnancy, it is avoided in the first trimester due to theoretical teratogenic concerns, though evidence is reassuring. The green frothy discharge is due to the organism's metabolic byproducts and the inflammatory response it triggers.
Why the other options are wrong
A. Azithromycin — Azithromycin is a macrolide antibiotic used for bacterial STIs (e.g., Chlamydia trachomatis, Mycoplasma genitalium) and is ineffective against Trichomonas vaginalis, which is a protozoan parasite, not a bacterium. This is a common NBE trap pairing STI with a broad-spectrum antibiotic without considering the organism's classification. C. Oral fluconazole — Fluconazole is an antifungal agent used for candidiasis (which presents with thick white curd-like discharge and vulvovaginal erythema), not trichomoniasis. While both cause vaginal discharge, candidiasis lacks the characteristic green frothy appearance and strawberry cervix. This option exploits confusion between common vaginal infections. D. Doxycycline — Doxycycline is a tetracycline antibiotic used for bacterial STIs such as Chlamydia trachomatis and Mycoplasma, not for parasitic infections. It has no activity against Trichomonas vaginalis. This is another antibiotic trap designed to test whether students can distinguish between bacterial and parasitic causes of STI.
High-Yield Facts
- Strawberry vagina (punctate hemorrhagic spots on cervix) is pathognomonic for Trichomonas vaginalis trichomoniasis.
- Metronidazole 400 mg BD × 7 days or 2 g single dose is the gold-standard DOC for trichomoniasis in India.
- Green frothy discharge is the classic presentation of trichomoniasis; thick white curd-like discharge indicates candidiasis instead.
- Trichomonas vaginalis is a motile protozoan parasite, not a bacterium—antibiotics are ineffective.
- Partner treatment is mandatory in trichomoniasis to prevent reinfection; it is a sexually transmitted infection.
- Metronidazole is avoided in first trimester pregnancy due to theoretical teratogenic risk, though evidence is reassuring; tinidazole is an alternative.
Mnemonics
GREEN FROTHY = TRICHOMONAS Green frothy discharge + strawberry vagina = Trichomonas vaginalis → Metronidazole. (White curd-like = Candida → Fluconazole; yellow mucopurulent = Chlamydia → Azithromycin.) METRO for TRICHO METROnidazole for TRICHOmonas. Remember: nitroimidazoles (metronidazole, tinidazole) kill protozoa; antibiotics kill bacteria.
NBE Trap
NBE pairs trichomoniasis with broad-spectrum antibiotics (azithromycin, doxycycline) to test whether students confuse parasitic infections with bacterial STIs. The strawberry vagina sign is the discriminator that rules out candidiasis (fluconazole) and bacterial causes.
Clinical Pearl
In Indian outpatient clinics, trichomoniasis is often misdiagnosed as candidiasis because both present with vaginal discharge. The key bedside discriminator is the green frothy appearance and strawberry cervix—once recognized, metronidazole is curative in >95% of cases, but partner notification and treatment are essential to prevent the ping-pong effect of reinfection common in Indian urban populations with multiple sexual contacts.
_Reference: DC Dutta's Textbook of Gynaecology (Ch. Sexually Transmitted Infections); Harrison's Principles of Internal Medicine Ch. 202 (Parasitic Infections)_