Current drain rises when digital input floats between '0' and '1' levels. To eliminate it do one of the following on all your unused digital inputs:
1) turn input to output using data direction registers
2) enable pull device, both pull-up and pull-down are OK.
3) pull inputs externally to I/O supply rails, usually vss or vdd
Since lower pin count packages may have non bonded out pin pads, you should not forget to turn them into outputs as well.
Edward