The Laws of Prayer (The morning services) (63)

1. One must keep “redemption” as close as possible to “prayer”. This means that one may not interrupt between the blessing of “Ga’al Yisrael” and the Amidah even by responding to Kadish or Kedushah or to say Amen to a blessing. (Shulchan Aruch and Mishne Berurah 111)

2. The saying of the verse which starts with “Hashem sefasai tiftach” is not considered to be an interruption as since Chazal inserted it into the prayer it has become part of the Amidah. (ibid)