Passing proglottids ("egg packets") is not a sign that parasite treatment is working. The sign that treatment is working is whne you pass head and whole body of tapeworm.
The life cycle of Dipylidium caninum, involves dogs, cats or humans as the definitive host and fleas or lice as the intermediate host. The perianal region of the dog or cat becomes contaminated with eggs when the eggs are passed in the feces, and the flea or louse ingests the eggs. The dog or cat (or human) is infected when they ingest a flea or louse infected with the metacestode state (cysticercoid).
The feces of an infected dog or cat (or human) may contain proglottids (often referred to incorrectly as "segments") that are shed from the tapeworm, and these have a characteristic size and shape of rice. Diagnosis of this species depends on finding proglottids or "egg packets" in the feces.