re = /;((?:[a-zA-Z]+ )+)(.*?);/m
str = '<pnr>0240978840</pnr>;Amplificator AD8622ARMZ;<upa>1</upa>
<pnr>0273101670</pnr>;Power Management LT1236BIS8-10;<upa>1</upa>
<pnr>0299801750</pnr>;Power Management LT1175IS8-5;<upa>3</upa>
<pnr>0233201780</pnr>;Amplificator LT1498CS8;<upa>4</upa>'
subst = '<kwd>$1</kwd><adt>$2</adt>'
result = str.gsub(re, subst)
# Print the result of the substitution
puts result
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for Ruby, please visit: http://ruby-doc.org/core-2.2.0/Regexp.html