Sounds like you are looking for a network metaanalysis.

https://bmcmedicine.biomedcentral.com/articles/10.1186/1741-7015-9-79

But you should get some expert statistical guidance on that, as those are even more complex and prone to Problems than classica metanalyses.

Dear Basma,

You could compare the results of separate meta-analyses: one of studies that evaluate treatment A, one of studies that evaluate treatment B, etcetera.

Another option would be to perform a subgroup analysis. You would then include all studies in one meta-analysis, but assign each study to a specific subgroup of studies. You can then assess whether the results within these subgroups are different from each other. Here you can find an example of a subgroup analysis could look like, and how to interpret the results: http://www.erim.eur.nl/research-support/meta-essentials/interpret-results/subgroup-analysis/

Good luck!

Henk

http://www.erim.eur.nl/research-support/meta-essentials/interpret-results/subgroup-analysis/

Dear Henk,

Thank you very much, your answer is very helpful .

Sounds like you are looking for a network metaanalysis.

https://bmcmedicine.biomedcentral.com/articles/10.1186/1741-7015-9-79

But you should get some expert statistical guidance on that, as those are even more complex and prone to Problems than classica metanalyses.

dear Basma,

If you want to asess the eficacy of a new treatment, you ever must compare with the gold standard, which is the best evidence of a treatment use in this moment. So I propose to conduct two separate reviews and meta analysis. All the best !!

 Dear Cecilia ,

Thank you for your answer , both treatment were found to be effective in other reviews  my  research question is which of the two drugs is more effective.No papers have compared them togeather yet. So, I wondered if  it is  possible to use indirect evidence by comparing their results versus the gold standered treatment to facilitate clinical decision .

 Dear Daniel,

Thank you very much.

Network meta analysis is the way to go. Good luck.

Did you try searching any  Randomized Controlled trial which compare the two treatments but not in a systematic review...? 

Regards,

Cecilia.