Is the effect of a slow release capsule nullified if the capsule is broken open and the contents are ingested?

Yes and No. Some slow release medications are meant to be removed and sprinkled over some sort of soft food ie. apple sauce and eaten. Just be sure the food is swallowed without chewing. These types of formulations are used a lot in long term care facilities. If the capsule is sealed and you open it and ingest the contents, now we're talking problem. Your Pharmacist is the person who is best suited to help in this situation. When in doubt ask! It's safer.