Today I went to ER and found I had shingles. I was prescribed Clindamycin, Valtrex &Prednisone. Upon picking up the prescriptions, the pharmacy was out of the Clindamycin. I went ahead and took the other two pills upon picking them up and then went to another pharmacy and got the clindamycin. By the time I took it, it had been a couple hours since I took the first to drugs. Bottom line, I feel that I am allergic to the clindamycin because within 30 minutes i had a headache that was obviously not your normal headache..it was intense, right behind my eyes and I also felt as if I was way out in left field...very, very out of it...no doubt a reaction to the drug. I have 500 mg Cephalexins I could take in place of the clindamycin 300 mg pills...but will this work effectively as a substitute? That is my question. Thanks.