Amoxicillin IV 1g 8 hourly

and

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

and

Metronidazole IV 500mg 8 hourly

If true penicillin / beta-lactam allergy:

Teicoplanin IV 12mg/kg (dosing table here) over 3-5 minutes as a slow IV bolus or over 30 minutes by IV infusion every 12 hours for 3-5 doses, then once daily

and

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

and

Metronidazole IV 500mg 8 hourly