transistor breakdown voltage?

I have a BC337 NPN rated 45v 500mA, I'm wondering will it be able to stop voltages above 45v when off or is the 45v rating similar to the breakdown voltage of a diode?

45V is the breakdown voltage of the part above which damage might be done to the part, so really this is no good for a 45V application. Generally I do not use components above 80% of their breakdown voltage and this should allow you enough margin to work with. Pick a higher voltage transistor (or a lower voltage application!)

Thanks, I was just wondering as I was designing a circuit where voltage along it is lower than 45v while on but can go above 45v at times while it's off.
I'll choose one with a higher voltage rating then.