The overarching principle in referencing or citing is that readers should be able to follow your sources if they are interested in finding out more about a topic.
You should always acknowledge other authors whose ideas or information you have used.
For further examples refer to Citing Medicine, 2nd edition - The NLM Style Guide for Authors, Editors, and Publishers.
Indirect citation is when the ideas of one author are published in another author’s text, but you have not read or accessed the original author’s work.
In the reference list, provide the details of the author of the work in which you found the quotation or idea - the actual source you looked at.
Make it clear in the text of your document that you are quoting a secondary source. If possible, always try and find the original work.
The AMA Manual section 3.13.10 states:
Reference may be made to one author’s citation of, or quotation from, another’s work. Distinguish between citation (work mentioned) and quotation (words actually quoted). In the text, the name of the original author, rather than the secondary source, should be mentioned. (See also 3.11.12, References to Print Journals, Discussants.) As with citation of an abstract of an article rather than citation of the original document (see 3.11.9, References to Print Journals, Abstracts and Other Material Taken From Another Source), citation of the original document is preferred unless it is not readily available. Only items consulted should be listed.
The forms for listed references are as follows:
1. Cauley JA, Lui L-Y, Ensrud KE, et al. Osteoporosis and fracture risk in women of different ethnic groups. JAMA. 2005;293(17):2102-2108. Cited by: Acheson LS. Bone density and the risk of fractures: should treatment thresholds vary by race [editorial]? JAMA. 2005;293(17):2151-2154.
2. Kato S, Sherman PM. What is new related to Helicobacter pylori infection in children and teenagers? Arch Pediatr Adolesc Med. 2005;159(5):415-421. Quoted by: Prazar G. How many pediatricians does it take to change a practice? or how to incorporate change into practice [editorial]. Arch Pediatr Adolesc Med. 2005;159(5):500-502.