Nina Karnik is the medical director of Holby City General Hospital and a consultant general surgeon working on the hospital's Acute Assessment Unit. Nina is the wife of cardiothoracic surgeon Matteo. She first appeared on 9 May 2017 as a friend of a patient and started working on AAU on 30th May 2017. Nina is portrayed by Ayesha Dharker

After Sam Strachan's resignation as medical director, Nina applies for the job and she is appointed by Hanssen. Nina wants to divorce from Matteo but he persuades her not to which leads to them sharing a passionate kiss. Nina's first day as medical director was shown in series 19 episode 43 "The Evolution of Woman". She got Guy Self to pitch at the commissioners for a way to decrease obsessive-compulsive disorder surgically which on a trial patient was a success. When Nina wants to cancel the operation, Guy threatens her to speak to Matteo about something 'he stopped her from doing in Berlin'. By episode 44 "Go Ugly Early", the board have decided to close down AAU's Trauma Unit and as Nina wants to excercise her authority on the ward, she is the bearer of bad news and tells clinical lead Ric Griffin and Trauma Unit lead Bernie Wolfe that the trauma section will be closed, ultimately leading to Bernie's resignation.