Unfortunately, he's going to need to be examined by a vet. Fishing line is notorious for becoming a linear foreign body inside of the intestines. With time, the line may lacerate the intestines requiring surgery. The more prompt the care the receives, the better. I would urge you to take him to an ER facility this weekend. If you need help finding one, please let me know your city, state and zip code.
Failing this, you can administer a dose of regular pepcid (famotidine) every 12-24 hours. You will want to give 0.5mg/pound of body weight (a 10# ***** would receive 5mg, a 5# ***** would receive 2.5mg, etc). For this, you can visit any human pharmacy and buy the OTC brand name Pepcid, or you can use the cheaper, off-brand “famotidine” that’s available. Either will be useful and should help reduce the vomiting you're seeing.
If he does stop vomiting and develops an appetite, boil chicken breast and rice together in water and once easily flaked, blend it together with more water to form a slurry he can drink. Give small amounts to start and increase as the hours go on. Ideally, this will help move the line through. If he's fortunate enough to pass this normally and you notice some line present at his anus do not pull but, instead, trim the line with scissors and allow it to pass from his body naturally.
I’ll be standing by if you have other questions. Let me know if I can help further.
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