First of all you should not go into your new position with the idea in your head that this is going to happen. If you do you can create a self fulfilling prophecy type situation. In all work situations there can be conflict and chaos. A good manager understands that the best situation is when a group of people work together as a team. If you can get the best out of your team it will be a win win situation. So how do you do that?
First and foremost you should treat everyone else the way you would like to be treated. If there is something you need done a certain way...phrase your request in a respectful manner. Yes, you are the pharmacist and they are the tech but only a naive manager will express this hierarchy structure in an overt fashion. Everyone there knows you are the boss, most will concede authority to you without a single syllable having to be communicated.
For those that attempt to challenge your authority, deal with them calmly, show NO emotion, not anger, not frustration, not sarcasm, etc. In a monotone voice state what the problem is....for instance, you ask the tech to do X task, and the tech tells you "Not now, later, when I finish blah, blah, blah. First of all, make sure you are right about asking the tech to do whatever it is you want before they handle what they are doing....if the tech is right regarding the priority you need to concede that fact graciously, however, you should comment about how they communicated the information to you. I would say something like, "I see that handling what you are is more time sensitive, so yes, continue doing that, but please in the future communicate with me in a less dismissive attitude. I don't want to feel I need to convince you to comply with my requests, because then we are going to have a hard time working together and that will not be fun for either of us."
If they were wrong however and were not doing a higher priority task then I would say to them, " Later is not okay, I need you to stop doing blah blah blah, and do what I have asked you to do right now. Do you understand?" Now hear me when I say that if you say those words and put any attitude into them you will have issues. Calmly saying those words with no inflection or tude is the way to go. You come across as professional and firm. And that is something most people respect. I would say that doing this requires practice and it may take time to hone this ability to communicate firmly but without any attitude.
As you are a new manager I would give you this advice....think before you speak...do not feel like you need to respond immediately. I have had some confrontational scenes in my nearly 20 year work experience where I just walked away to think about how I wanted to deal with the situation, always I made the decision to calm down before I said or did anything. As a result, I was able to come back, calmly deal with a potentially explosive situation, maintain control of my area/employees, and most importantly get on with the business of the day.