In this paper, general, easy to compute, exact expressions for the probability density function, cumulative distribution function and average value of the ratio of independent non-identically distributed κ-μ random variables, with arbitrary parameters, are derived. As an application example, capacity analysis of spectrum sharing systems undergoing κ-μ fading is provided. Specifically, expressions for the outage capacity with peak interference power constraint, the delay-limited capacity, and the ergodic capacity with average interference power constraint are derived. Numerical results are shown in order to investigate the effect of the fading parameters on the system capacity.