Without culture/sensitivity results, you're just kind of shooting hit-or-miss, with regard to selection of antimcrobials. But, in my hands, oxytetracycline (the active ingredient in LA-200 and the like) is USUALLY pretty effective in treating metritis in ruminants; won't work on all of them, but most...
But, I also couple that with administration of prostaglandin injections to short-cycle them - and, in truth, the prostaglandins may do more good than the antibiotics.
Uterine boluses...I used 'em 30 years ago; not sure they're really all that helpful or effective, but probably don't hurt anything.