The tablet that you have given is for internal parasites, you should give Ivermectin tablet as I suspect the dog might be having external parasites. The tablet Ivermectin has to be given as per body weight.

Itchiness couldd be due to so many. We may need to check the pet before prescribing medications

It's a good thing that you have dewormed the dog...Use that tablet only after 3 months...now... As you said that it was a street dog...there is a lot of chances that it might be having tick or mite infestation... I would suggest you a treatment regime...that you'll need to strictly follow with caution... Liquid Vitraz 2-5ml Shampoo Clinar M Tab wysalone 5mg 10 tablets Tab lexin 250mg.    10 tablets Syrup Vitabest derm

Hi, Chronic itching around the body, tail nd neck is often due to external parasite, skin inf. , fungal issue/ allergies. Since she hasn’t received any veterinary care or vaccinations yet, it’s important to proceed carefully nd avoid over-the-counter treatments without proper guidance. Points I suggest here: Please take her for a veterinary consultation, where a proper skin examination can be done. The vet may recommend skin scrapings or  other tests to identify the exact cause. Avoid using human medicines or syrups, as they can do more harm than good. Regular bathing with appropriate dog-friendly medicated shampoos may help, but only after the vet identifies the underlying cause. Continue providing gud nutrition nd regular dewoming under vet supervisn. Since the itching has lasted several month, it’s imp. not to delay. Early diagnosis and treatment can give her much-needed relief. Wishing her a speedy recovery.. Dr. SY🙏

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Demodicosis is classical skin problem. Other reasons also contribute to itching in dogs.