Injection spear

From PathfinderWiki

An injection spear is an exotic two-handed melee weapon used to inject a liquid when a target is hit, if the wielder is skilled in the use of the weapon. Up to five doses of a liquid can be stored in the spear's reservoir. Unlike other spears, an injection spear cannot be thrown or used to brace against charges.1

Injection spears are a dero specialty, though the design has been mimicked by gnolls and xulgaths.12