Most of them follow some basic guidelines:
1. 3 (or 5 syllables)--emphasis on the first syllable (and 3rd syllable)--this rule is the most flexible
2. 4 syllables--emphasis on the second syllable
These rules can be overridden if the drug has a "common" name part within it that must be pronounced a certain way.
3 syllables--BUSpirone, CLOnidine, GLYburide, TRAmadol (with obvious exceptions such as metFORmin, diGOXin)
4 syllables--fluOXetine, liSINopril, amLOdipine, carVEdilol
5 syllables--CARbaMAZepine, FEXoFENadine, OselTAMivir
Some exceptions due to "common" name parts:
Statins--SIMvaSTAtin (b/c "statin" should be heard in the name)
Tetracyclines--DOxyCYcline (b/c "cycline" should be heard)
Yes, you can break each one of these...but they're guidelines that I think have at least some merit.