Metronidazole is effective in all of the following conditions except –
**Core Concept**
Metronidazole is an antibiotic and antiprotozoal medication that acts by inhibiting the synthesis of DNA through its active metabolite, which is a nitro radical. This mechanism targets anaerobic bacteria and protozoa, making it effective in treating various infections.
**Why the Correct Answer is Right**
Metronidazole's effectiveness is due to its ability to target anaerobic bacteria and protozoa by inhibiting DNA synthesis. It is commonly used to treat infections such as bacterial vaginosis, pelvic inflammatory disease, and amoebic dysentery. The medication is also effective in treating giardiasis, a parasitic infection caused by Giardia lamblia.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as metronidazole is effective in treating bacterial vaginosis, which is caused by anaerobic bacteria.
**Option B:** This option is incorrect as metronidazole is effective in treating amoebic dysentery, which is caused by Entamoeba histolytica.
**Option C:** This option is incorrect as metronidazole is effective in treating giardiasis, which is caused by Giardia lamblia.
**Option D:** This option is incorrect as metronidazole is effective in treating trichomoniasis, which is caused by Trichomonas vaginalis, a protozoan parasite.
**Clinical Pearl / High-Yield Fact**
Metronidazole is contraindicated in patients with porphyria, as it can exacerbate this condition. Additionally, metronidazole can cause a disulfiram-like reaction when combined with alcohol, leading to symptoms such as nausea, vomiting, and flushing.
**Correct Answer:** D.