When should I use ‘et al’ in AMA citation format?
The names of up to six authors should be listed for each source on your AMA reference page, separated by commas. For a source with seven or more authors, you should list the first three followed by ‘et al’: ‘Isidore, Gilbert, Gunvor, et al’.
In the text, mentioning author names is optional (as they aren’t an official part of AMA in-text citations). If you do mention them, though, you should use the first author’s name followed by ‘et al’ when there are three or more: ‘Isidore et al argue that …’
Note that according to AMA’s rather minimalistic punctuation guidelines, there’s no period after ‘et al’ unless it appears at the end of a sentence. This is different from most other styles, where there is normally a period.