From what a fireman told me, ALL fire extinguishers are one-use.
If the head is metal, it's probably refillable, and it should be refilled by a professional after any discharge (the fire dept can recommend one). If any part of it is rusty or corroded, they probably won't refill it.
The ones with the plastic heads aren't refillable; if the tank is aluminum, take it to a recycling facility. If it's made from anything else, send it to the dump.
Sue
Well no, commercial extinguishers for home use generally are one-use, but the heavy duty industrial once's can be refilled, many many times and will last for many years.
Fire extinguishers are checked every year and every some years they will be empyted and hydro tested (to check it's pressure risistance). Than dryed and refilled. There have been 2 cases where a extinguisher tank failed and killed the user, because of hidden rust. I think it was hidden behind the rubber protective foot on the bases of those extinguishers, where water would collect...