According to producer it is effective against all ticks. This particular item protects dogs up to 4 kg. For efficient protection it is recommended to use the correct product for the actual weight of your pet.

Nexgard treats and prevent all kind of ticks and sarcoptic mange (ear mites)

こちらが最小サイズのネクスガードになります。2kg以下の犬については、フロントラインプラスというノミ・マダニ予防薬をおすすめします。
https://jp.petbucket.com/p/9122152/frontline-plus-small-dogs-under-22lbs-10kg---6-pipettes.html

We recommend to buy correct size for each dog. As you can't be sure, you have exactly the half of the active ingredient on each part even you cut it in half.

Our stock rapidly changing so we can't give exact date but on average you have about 2 years before the expiry date is reached so you won't have any problems base on expiry dates.