Introduction Pharmacovigilance is now changing to become a proactive discipline to avoid harm from drugs in patients. Effects of drugs during breastfeeding remain underevaluated and underresourced. Most lactating women are prematurely stopping breastfeeding when they need to take medicine treatment.

Methods We formed a group in Paris in 2006, composed of a paediatrician, specialised nurses in breastfeeding, a pharmacologist and methodologist to provide health professionals and patients with up-to-date information. Medic-Al network will facilitate discussion about pharmacokinetic data in maternal milk and allow comparative study about potential benefits and risks.

Results We report a case to the pharmacovigilance center. A full-term female infant of 2695 g birth weight was delivered vaginally. At 10 days, she had recovered her birth weight. She was lethargic and she had difficulties in breastfeeding. Seven days later, the mother had less milk and she decided to stop breastfeeding. Six capsules of dextroproxyphene a day from day 0 to day 10 was prescribed to reduce the episiotomy pain. Our network decided to measure the hair concentration of propoxyphene and norpropoxyphene at day 13. These pharmacological data were in favour of newborn intoxication by propoxyphene through breastfeeding.

Conclusion Pharmacology clinical research is enhanced through this network in the area of lactation. The early detection of a risk is discussed, through the Internet, with colleagues of the French and European Pharmacovigilance Network (CRPV, AFSSAPS, EMEA). Fast publication in collaboration with the journal Prescrire allow a proactive communication with general practitioners and health professionals to modify unsafe practices.