I want it to capitalize the first letter of an expanded acronym used at the start of a sentence, like:
Application programming interfaces (APIs) are ...
I tried to define a new command \Acp for that purpose:
\usepackage[smaller,nohyperlinks]{acronym}
\acro{API}{application programming interface}
\newcommand{\Acp}[1]{\MakeUppercase\expandafter\acp{#1}}
However when I use it, it doesn't work as desired:
\Acp{API} are ...
produces
application programming interfaces (APIs) are ...
Unfortunately I can not use the glossaries package which accomplishes exactly that due to interpackate-incompatibilities.
I had a similar desire in the list of acronyms where I also wanted to capitalize all first letters. There I redefined a different command as suggested in Capitalize the first letter in acronym list:
\makeatletter
\patchcmd{\AC@@acro}{] #3}{] \MakeUppercase #3}{}{}
\patchcmd{\AC@@acro}{] #3}{] \MakeUppercase #3}{}{}
\makeatother
That works.

glossaries? (I thinkglossariesis probably the best solution to this problem, so I am hoping that one can identify and fix the incompatibilities.) – mforbes Aug 22 '12 at 16:22