The last line of this episode is "Guys, we have an airplane accident to talk about". This is a reference to "Medico de familia". When the previous season of that series ended, the last moment of that last chapter was that the two main characters were involved in an airplane accident with unknown ending. After this episode, the new season of "Medico de familia" was about to start, to give solution to the fate of these two characters.
The character Clara Nadal, played by Belen Rueda is a character that appeared first in Medico de Familia, exactly the same character and the same actress
The character Nacho Martin, performed by Emilio Aragón, is the main character in "Médico de familia". Aparently, this character has a long friendship with the Lourdes, main character from "Farmacia de guardia", so, both series are linked.
