Route poisoning is a way to prevent routing loops. Distance-vector routing protocols in computer networks use route poisoning to indicate to other routers that a route is no longer reachable and should be removed from their routing tables. A variation of route poisoning is split horizon with poison reverse whereby a router sends updates with unreachable hop counts back to the sender for every route received to help prevent routing loops.
Some Distance-vector routing protocols use a maximum hop count to determine how many routers traffic must go through to reach the destination. Each route has a hop count number assigned to it which is incremented as the routing information is passed from router to router. A route is considered unreachable if the hop count exceeds the maximum allowed. Route poisoning is a method of quickly removing outdated routing information from other router's routing tables by changing its hop count to be unreachable (higher than the maximum number of hops allowed) and sending a routing update.
As Amine said, Split Horizon is another way to avoid looping.
Also, convergence time for routing tables the presence of erroneous loops can be reduced using "triggered updates" i.e changed routes can be advertised immediately for quick propagation of topology changes in the network