▁United ▁States ), ▁the ▁active ▁ing red ients ▁used ▁in ▁the ▁F DC s ▁are ▁unlikely ▁to ▁exhib it ▁ad verse ▁drug ▁interactions ▁with ▁each ▁other . ▁However , ▁F DC s ▁may ▁interact ▁with ▁other ▁dru gs ▁that ▁a ▁patient ▁is ▁taking , ▁so ▁the ▁usual ▁medical ▁and ▁ph arma ce ut ical ▁pre ca utions ▁against ▁drug - d rug ▁interactions ▁or ▁D D Is ▁remain ▁war r anted . ▁F DC ▁drug ▁products ▁may ▁be ▁developed ▁by ▁a ▁ph arma ce ut ical ▁company ▁as ▁a ▁way ▁to ▁in ▁effect ▁extend ▁propriet ary ▁rights ▁and ▁market ability ▁of ▁a ▁drug ▁product . ▁Since ▁F DC s ▁may ▁be ▁protected ▁by ▁pat ents , ▁a ▁company ▁may ▁obtain ▁exclusive ▁rights ▁to ▁sell ▁a ▁particular ▁F DC ▁or ▁form ulation ▁there of , ▁even ▁though ▁the ▁individual ▁active ▁ing red ients ▁and ▁many ▁th era pe ut ic ▁uses ▁there of ▁may ▁be ▁off - pat ent . ▁ ▁Dis adv antages ▁▁ ▁There ▁may ▁not ▁be ▁an ▁F DC ▁available ▁with ▁the ▁appropriate ▁dru gs ▁and / or ▁in ▁the ▁most ▁appropriate ▁respective ▁strength ( s ) ▁for ▁a ▁given ▁patient , ▁which ▁can ▁lead ▁to ▁some ▁patients ▁getting ▁too ▁much ▁of ▁an ▁ing red ient ▁and ▁others ▁getting ▁too ▁little , ▁as ▁the ▁AA O ▁notes ▁that ▁F DC s ▁" limit ▁clin icians ' ▁ability ▁to ▁custom ize ▁dos ing ▁reg im ens ." ▁In ▁such ▁cases ▁an ▁alternative ▁possibility ▁( inst ead ▁of ▁an ▁F DC ) ▁is