I Just Received Two Medications For A Spasm In A

I just received two medications for a spasm in a back muscle. I was only expecting to get a scrip for one according to the conversation that I had with the doctor. The meds are Chlorzoxazone (500 mg) and Tizanidine (4 mg). The Chlorzoxazone instructions say1 tablet by mouth q 6 hr, p.r.n. and the Tizanidine instructions say1 tablet by mouth q 8 hr, p.r.n.

Am I suppose to take both meds?

With similar muscle spasms before when I had two meds there was one to take at bedtime (due to possible drowsiness) and one for day time use. However, the instructions do not say anything about this.