"When you are a hammer, the world consists of nails"
Person A is speaking to Person B about something which is meaningful to A
Their (unstated) outcome for the conversation is to have a conversation where they are listened to and the experience and subject explored.
Person B then interrupts person A
This has to be done by one or a combination of:
Talking over them; ('Bullhorning' )
By A's non-verbal messages overpowering A's message (eg B head-shaking violently side to side);
Waiting for A to breathe / end a sentence and then talking in the gap ('Grabbing the mike')
I found this paper
http://interruptions.net/literature/LaFrance-PWQ92.pdfWell worth reading. (I tried copying sections from the PDF but was not successful)
I appreciate that the 'power' dimension self-evidently exists - personally, I think that framing the problem in a communication domain would make it much more amenable to change in the wider population rather than framing it in purely social / economic or gender domains.
I am very aware of the pattern in action and that the OP misses the report of the other person in the conversation and of a third party observer. My best mate does this a lot and I found the best solution for me. He interrupts by talking over. I have found that one or more of these strategies are really useful:
a) If what he says is very tangential to my subject, I will just start speaking slightly slower than him, in a sing-song friendly tonality "And interesting. And you have not heard the end of my story." Repeat like a mantra

b) Relevance challenge
"I'm unsure how Y is directly connected to my conversation. I hadnt finished sharing about X and would like to do that"
c) Meta-communication Interrupt
"Petunia" said in a slow louder voice.
Unless the conversation was around flowers, this acts as a conversational Control-Alt -Del for a few seconds. State your outcome for the conversation and start from the point before the interruption.

A lot of the people who are mega-interrupters / derailers have limited sensory acuity about the effects of their interruptions (they are literally only listening to themselves) - I think of them like bulls - pretty difficult to 'push' them in a different direction, but find the ring through their nose and you can gently lead them in a more mutually empowering, respectful and productive direction.