Why use sed at all, you can do it all in Perl?

knoppix@Microknoppix:~$ perl -Mstrict -wE '
> my $pbxiplp = <<EOF;
> (3.3.3.3,4.4.4.4,)
> EOF
> print $pbxiplp;
> 
> my $pbxiplp1;
> open my $inFH, q{<}, \ $pbxiplp or die $!;
> open my $outFH, q{>}, \ $pbxiplp1 or die $!;
> while ( <$inFH> )
> {
>     s{ , (?= \) ) }{};
>     print $outFH $_;
> }
> close $inFH or die $!;
> close $outFH or die $!;
> 
> print $pbxiplp1;'
(3.3.3.3,4.4.4.4,)
(3.3.3.3,4.4.4.4)
knoppix@Microknoppix:~$
[download]

I'm using scalar refs. here as I'm doing this on the command line but it would work just as well with real files.

I hope this is helpful.