Some of the drugs are having side effects associated with oral administration with less bioavailability...Please share your latest ideas about drug molecules belonging to this category
It depends on what you are looking for. Consider Simethicone as an instance, the drug acts within gastrointestinal tract while not being systematically absorbed into the blood meaning (almost) zero bioavalibility. Some other drugs act within the same location while minimally absorbed such as Mebendazol. If you could provide more details, may clearer answer you get.
Your answer is clear. Large molecules that do their action in GI tract could be candidate for your question.
Bulk-forming agents could be your answer, while they will not be absorbed into systemic blood circulation. Other drugs such as antacids and sucralfate absorbed to systemic blood circulation less than 5%.