$ perl -le '$_ = q{Dr P J van Houten MD};
> s[(?<=[A-Z])(?=\s)][.]g;
> print;'
Dr P. J. van Houten MD
$ perl -le '$_ = q{Dr P J van Houten MD FRCS};
> s[(?<=[A-Z])(?=\s)][.]g;
> print;'
Dr P. J. van Houten MD. FRCS
$