These printers use the KX-P450 cartridge:
Panasonic Fax KX-4450
Panasonic Fax KX-4451
Panasonic Fax KX-4455
Panasonic KX-P 4450
Panasonic KX-P 4450 I
Panasonic KX-P 4451
Panasonic KX-P 4455
Panasonic UF 725
Panasonic UF 750
Panasonic UF 750 D