RUQ pain, fevers, increased alkaline phosphatase and bilirubin.
Having or having had prior biliary disease, stones, obstruction, or having your biliary tract manipulated.
Parasites: Ascaris lumbricoides.
First, look for away cause of obstruction that you can relieve. Generally speaking, E. coli and B. fragilis can be used as stand ins for all community acquired gram negative rods and anaerobes, respectively. So kill the gram negative rods with third generation cephalosporins OR quinolones PLUS kill the anaerobes with metronidazole OR clindamycin. There is too much resistance in E coli to rely on piperacillin and ALL other penicillins if you do not have cultures validating susceptibility.
You probably get the best results with drugs that good biliary levels, so my preference is ceftriaxone and metronidazole. FYI, the other drugs that get good biliary levels are piperacillin (but no so much tazobactam), nafcillin and clindamycin.But the best drug, as always, is draining the pus. Monotherapy with a carbapenem OR penicillin/beta-lactamase inhibitors are used by some. Not me. If septic, add a short course of gentamicin. Remember, gentamicin levels in bile fluids are squat.
If there is good biliary drainage, the patient can probably be changed to po after three days even if bacteremic (PubMed) instead of the standard 10 days.
Beware the ICU gallbladder. A ventilated patient, often a diabetic, with fevers and a normal US of the gallbladder, but an elevated ALP. Often a gangrenous gallbladder is found at surgery. Me? I can't figure out a HIDA, so I nearly always call a general surgeon.