Yes, ode45 can be used for higher-order differential equations. You need to convert the higher order equation to a system of first-order equations, then use ode45 on that system.
For example, if you have
... u'' + a·u' + b·u = f
you can define u1 = u, u2 = u' and now you have the system
... (u2)' + a·u2 + b·u1 = f
... (u1)' = u2
Rearranging, this is
... (u1)' = u2
... (u2)' = f - a·u2 - b·u1
ode45 is used to solve each of these. Now, you have a vector (u1, u2) instead of a scalar variable (u). A web search regarding using ode45 on higher-order differential equations can provide additional illumination, including specific examples.
