Concerns About Mebendazole and Metronidazole Drug Interactions - Family Medicine

Dr. Xiao Yongxun reply Family Medicine

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Dear Ms.
Ellie:
1.
Mebendazole is a synthetic benzimidazole compound that is widely effective against nematodes.
This medication is the first-line treatment for whipworm (Trichuris trichiura), pinworm (Enterobius vermicularis), hookworms (Necator americanus and Ancylostoma duodenale), and protozoan infections (Ascariasis lumbricoides).
Mebendazole works by binding to the microtubules of the parasites, disrupting their structure, and reducing glucose absorption in the worms.
The affected parasites are expelled in the feces.
Mebendazole is nearly insoluble in aqueous solutions.
A small oral dose (chewed) is absorbed by the body, unless taken with high-fat foods.
This drug undergoes first-pass metabolism, resulting in inactive compounds.
The toxicity of Mebendazole is relatively low, although patients may report abdominal pain and diarrhea.
Additionally, due to its teratogenic and embryotoxic effects observed in test animals, it is contraindicated in pregnant women.
2.
Metronidazole (Frotin Enteric Sugar®) is the first-line mixed anti-infective agent for treating amoebic infections, as it kills the trophozoites of E.
histolytica.
Metronidazole has also been found to be broadly effective against infections caused by Giardia lamblia, Trichomonas vaginalis, anaerobic cocci, and Gram-negative anaerobic bacilli (e.g., Bacteroides species).
It is the preferred medication for treating pseudomembranous colitis caused by the Gram-positive anaerobic bacillus Clostridium difficile, and it is also effective for brain abscesses caused by these pathogens.
The most common adverse reactions are gastrointestinal-related, including nausea, vomiting, upper abdominal discomfort, and abdominal cramping.
An unpleasant metallic taste is often reported.
Other adverse reactions include oral candidiasis (oral fungal infection) and, rarely, neurotoxic issues such as dizziness, vertigo, and peripheral neuropathy or sensory abnormalities.
3.
The above information is primarily extracted from personal lecture notes for students and is for reference.
Since you have already taken the medication and have not experienced significant side effects, it is advisable to drink plenty of water and urinate frequently to help eliminate the drug and its metabolites, so there is no need for excessive concern.
In fact, it has been over four days since you stopped the medication, which corresponds to three to four half-lives; theoretically, you should be fine.
4.
"Recently, there has been an issue with anal itching, which is often bothersome at night." This has been assessed as a parasitic infection without other corroborating evidence; indeed, this lacks precision.
In recent decades, due to the need to sustain a large population, there has been extensive use of chemical fertilizers and pesticides to increase agricultural yields, resulting in a clinical landscape where parasitic or worm infections are rarely seen.
Unless it is an imported case or purely organic cultivation, such occurrences are quite rare.
Instead, conditions like hemorrhoids, chemical irritant dermatitis, bacterial infections, and fungal infections are more commonly observed.
5.
Regarding the issue of "having diarrhea continuously since before taking Mebendazole": in addition to parasitic infections, one should also consider common functional gastrointestinal syndromes, irritable bowel syndrome, hyperthyroidism, acute gastroenteritis, ulcerative colitis, Crohn's disease, and colorectal tumors.
6.
Therefore, it is recommended that you consult with your family physician for examination and discussion, or directly visit a gastroenterology clinic for treatment.
7.
As for the symptoms of a cold, maintaining a balanced diet and getting sufficient sleep should lead to improvement.
If there is no improvement, you should seek medical attention.

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Reply Date: 2019/11/14