The answers to the below questions will help you determine whether your search is complete or whether you need to continue.
How many citations did I find? If you have found too few citations, consider searching more databases, broadening your search terms, or searching a larger time span. If you find too many citations, perhaps you can limit or narrow your search terms to be more specific.
Are my keyword terms related to my protocol? Make sure that the words you use to search are relevant to your research
What keyword terms did I use for animal testing alternatives? The NIH Library suggests that only using "terms for painful aspects" and using the term "alternative" without other synonyms could be a red flag for IACUCs and other investigatory bodies.
How many places did I look? Because the literature on animal research methods falls into so many different interdisciplinary areas, it is necessary to search more than one database.
Did I set up my search strategy appropriately? Databases may return odd results because they are confused by how you formulated your search. It will help to check the search tips or help pages in unfamiliar databases for strategies unique to the database.
Have I searched an adequate time period?
It is important to examine the literature from a time period longer than the last few years in order to fully examine possible alternatives.