since your sister is the one treating you with her (unfinished) medication perhaps this question should be directed to her. i am never of fan of this practice. i think it is dangerous. since many illnesses are viral antibiotiics do absolutely nothing. apparently the medical provider at urgent care did not feel that you needed any antibiotic let alone a sulfa drug or azithromycin. the fact that a z-pack has worked for you in the past in no way implies that each year you have the same identical bacterial infection that responds to azithromycin. statistically this would be highly unlikely. illnesses do change over time. most people get better on their own but a few do get worse. if you feel you are now sicker than when you were evaluated by urgent care than it would be better to be re-evaluated again. perhaps you do need an antibiotic now but there is no way for me to make that determination over the internet. this would be the right thing to do. taking someone else's leftover antibiotic is not.
is it safe to mix sulfameth/trimethoprim with a z-pak? . urgent care wouldn't prescribe me an antibiotic bc i haven't been 'sick long enough'. they prescribed me cheratussin ac syrup and to buy otc medicine. my sister brought me some of her medicine sulfameth/trimethoprim saying it was the same thing. i've taken 2 doses. 1 pill at 9pm and 1 pill at 9 am. i'm still as sick as ever. gained more symptoms of loss of appetite wanting to puke at the taste/smell of food a head ache and an ear ache. i get sick once a year and a z-pak always fixes me