You would be very hard put to justify Medicare picking up the drug bills of elderly Americans as "promoting the general welfare," even if that clause was to be as loosely interpreted as you suggest. Burdening our posterity with today's excessive prescription drug bills is hardly consistent with the Preamble that you quote. Indeed, Medicare itself is a disaster rushing to happen, and very far indeed from the intention of those wise men, who sought to secure the blessings of liberty to their posterity. (For more on Medicare, see Medicare--Panacea or Death Potion?.)
Even aside from the Constitutional question, there is no possible way that this can work in the long run, given the trends in medicine, public avarice and demographics. Congress is engaged in colossal demagoguery over this.
William Flax Return Of The Gods Web Site
If we (the electorate) are sending to Congress individuals who are fiscally responsible and realize the necessity of finding ways for the citizens to provide for themselves, then we can regain the vision of the Founders. The need for legislative help for prescription drugs is only a symptom of a larger problem from previous legislation on insurance policies and food and drug policies that have grown way beyond any recognizable standard of good common sense.
I see each Congress piling on to previous problems and never stopping to reorganize or reprioritize how our tax monies are spent. To the elected officials it appears to be easier to tax more and spend indiscriminantly on any and everything possible that will quiet those who are in need. I also believe that there is legitimate cause for budgetary expenditures for those who are not able to care for themselves. It's unfortunate that where the church once cared for particular personal needs of the citizen our tax monies have now been designated as a part of supplying personal needs.
Now we can both say there is no way that our Government can create law to provide for prescription drugs, but if we are demanding this, what solution must happen to make sure this need is met at the local level? And how do we select principled men and woman that will have the capability to turn the direction to personal responsibility not only in personal lives but in business?
It's men like Arlan Spectre that is making statements regarding British Law, as in the example of the impeachment of Clinton that I find disturbing. How many really know the Declaration of Independance and our U.S. Constitution to actually insure that it will continue as seen by the Founders?
With all my opinions I must say I'm not a political scholar so consider the source of my understanding on prescription drugs.