Gentamicin IV (dosing info here) - use booking weight and monitor renal function daily.

If long term urinary catheter or urological stents present add amoxicillin IV 1g 8 hourly.

If positive urine cultures are available, therapy choices should be based on the released sensitivities.

If true penicillin / beta-lactam allergy:

Gentamicin IV (dosing info here) - use booking weight and monitor renal function daily.

Gentamicin should be avoided in patients with decompensated liver disease (jaundice, ascites, encephalopathy, variceal bleeding or hepato-renal syndrome). 

If the use of gentamicin is contraindicated, the agent should not simply be omitted, but an alternative regimen should be chosen. 

Review gentamicin after 72 hours, as there is a risk of ototoxicity associated with prolonged use. If no positive cultures are available to guide therapy at this point, an alternative empirical regimen can be discussed with an infection specialist.