$ perl -wle '$_ = "142,143"; s/(,42|42,|\b42\b)//g; print'
    1143

##</code><code>##

    s/,42\b|\b42,|^42$//;   # Or
    s/\b(?:,42|42,|42)\b//; # Or
    s/\b42,|,?42\b//;