Switching rates of multistep reactions

We consider the switching rate of a metastable reaction scheme, which includes reactions with arbitrary steps, e.g., kA <->(k+r)A (both forward and reverse reaction steps are allowed to happen). Employing a WKB approximation, controlled by a large system size, we evaluate both the exponent and the preexponential factor for the rate. The results are illustrated on a number of examples.