Image source: Getty Images.Shares of global drug giant Pfizer (NYSE: PFE) had a pretty miserable October, ending lower by 6.4% based on data from S&P Global Market Intelligence, and things haven't improved through the first few days of November following its third-quarter earnings results. The weakness appears to primarily lie with the uncertainties surrounding prescription-drug reform.With plenty of news hitting the wires in October but nothing that was notably bad, the best explanation for Pfizer's weakness probably boils down to what might happen to drugmakers' pricing power once a new president is in the Oval Office.