You could use something like this Heike:
"On the other hand/Conversely/However, the bulking agent/extender/filler causes the carrier-medication-unit to break up/fall apart/disintegrate in the gastro intestinal tract...."
or
"On the other hand/Conversely/However, the bulking agent/extender/filler brings about/triggers disintegration/break-up of the carrier-medication-unit in the gastro-intestinal tract...."
Something like that

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Note added at 3 days17 hrs (2013-04-02 07:53:40 GMT)
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Right Heike - for Cilian's benefit.... Träger should be "excipient" (a pharmacologically inactive substance used as a carrier for the active ingredients of a medication). I think we would tend to use "active substance" rather than medication for "Medikament". So the "carrier-medication-unit" might be better translated as "the combination of the excipient and the active substance". I have no idea for Füllstoff (normally just "filler" but perhaps/presumably there is a better term for it in English in a medical/pharmaceutical context) - difficult to tell without more context and I am no medical expert and have not got time to find out. If you have any further questions about the rest of the text or if you would like an English native-speaker to proofread the rest of your translation and come up with something sparkling and above-standard then please contact Cilian directly!!