Impact of osmolality on burning sensations during and immediately after intramuscular injection of 0.5 ml of vaccine suspensions in healthy adults.

A randomised placebo controlled double-blind cross-over trial was performed on twenty healthy adults to assess the effect of osmolality (300,600,850 and 1100 mOsm) on local tolerance of an intramuscular injection (0.5 ml) of five suspensions containing the same components as the excipients of a combined Diphtheria-Tetanus-acellular Pertussis-inactivated Poliomyelitis-Haemophilus influenzae type b paediatric vaccine (DtacP-IPV-Hib, PENTAVAC). The results did not show any dose-effect relationship between burning or pain sensations and the different osmolalities tested. Although mild and not clinically relevant, these sensations seemed to occur more frequently following injection of an isotonic saline solution (P<0.05). Thus, the osmolality of vaccine like suspensions does not appear to be a potential cause of local pain or burning sensation after their administration.