I had 40mg prednisone plus a pepcid (famotidine) for rash sun night then 40mg again plus a pepcid (famotidine) yesterday afternoon when is it safe to drink beer or liquor?

Yes: It is safe just do not over do it. A couple is fine.

Alcohol: In general will rev up your liver metabolism, thereby reducing efficacy of certain medications, while other times it may increase their toxicity. Use good judgment and moderation always.

Alcohol use: Alcohol is a biologically active substance which interacts with medications directly or indirectly so it is best to avoid using alcohol together with medications. For most medications it should be ok to enjoy a little alcohol 24 hours after the last dose. Avoid driving or using machinery when using alcohol. Limit usage to two small measures a day for men and one for women.