* "Tranquillize" is a verb, meaning to make calm or peaceful. Adverbs modify verbs, adjectives, or other adverbs.
* Directly related adverbs are uncommon for this verb.
However, you can use phrases or other adverbs to convey the same meaning:
* Calmly: "He calmly tranquillized the agitated patient."
* Soothingly: "The doctor spoke soothingly to tranquillize the anxious child."
* Effectively: "The medication effectively tranquillized the animal."
* Quickly: "The nurse quickly tranquillized the distressed patient."
The best choice will depend on the context and the specific nuance you want to express.