Kelham, who started at MS&L last week, has joined from Chiron where she was market access manager in the biotech firm's marketing department.
She will work on the agency's global remit to promote pharma giant Sanofi-Aventis's pre-launch drug Acomplia.
Kelham is part of a 15-strong London-based team dedicated to global work and reports to UK healthcare director Sally Bradford.
Prior to Chiron, she worked for medical comms consultancy Westaway Gillis for six years. Before that she spent eight months in a sales job at Abbott Laboratories. She has also worked at Searle Laboratories.
Kelham sits alongside fellow associate director Rachel Allen in MS&L's UK healthcare team dedicated to global clients. Allen joined earlier this month (PRWeek, 8 April).
Explaining her decision to move into PR, Kelham said: 'The pharma sector is so heavily regulated but PR allows you to get creative.'
Chiron hit the headlines last year when UK regulators suspended its licence to manufacture Fluvirin. The Government lifted its suspension last month.