I took physiology over summer, but I was in the quarter system so it went by fast! If it had anatomy lab, it would have been too hard to add on pharmacology as well. It is not impossible, but your summer will be taken away with very rigorous classes and a lot of studying!
Side note: from what I remember, pharmacology is not necessary for admission to medical school. It wont help much on the MCAT either. Unless you need it for your major, then I would hold off on taking it if you're premed.