Which type of preparations allows drug effects to continue at the same level over a long period?

The answer is: sustained (or extended) release preparation.

A sustained-release medication is a drug whose release of the active ingredient is controlled over time, that is to say, that it diffuses more slowly and longer in the body.
These medications can be any type of preparation, it could be tablets, capsules, ophthalmic or dermal insert, suppository...

What some science videos to you

The return of the wolf to yellowstone national park will probably affect the bird population to some degree, not significantly. while wolves will hunt birds when necessary, they prefer to hunt larger prey. the bird population will most likely only be affected when hunting is scarce for the wolves. birds of prey will also probably not be affected as much as other birds who spend more time on the ground hunting for food as the tend to spend more time in the air or in trees since they do not need to stay on the ground for long due to the nature of the way they hunt.