The present invention relates to compounds, peptides, peptidomimetics and pharmaceutical compositions that inhibit protease activity and the use of these compounds, peptides, peptidomimetics and pharmaceutical compositions to treat or prevent a condition. In particular the condition may be periodontal disease. The compounds, peptides and peptidomimetics may be derived from various caseins, for example α-casein, β-casein and κ-casein. The protease activity which the compounds, peptides, peptidomimetics and pharmaceutical compositions of the invention inhibit includes that of the gingipains.