Why is gold sol used for intra-muscular injection?

In my textbook it is written that gold sol is used for intramuscular injection. But, actually what is its use? Why would people use such a precious element for injection. Can other colloids be used like silver sol? 


Note:I posted this question to get a deeper understanding of what is given in my text about the use of gold sol in intramuscular injection. Googling it didn't help. 




Will this help?


[Toxicity and cellular uptake of gold nanoparticles: what we have learned so far?](http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2988217/)


Gold has a long tradition as a disease-modifying antirheumatic drug in the treatment of rheumatoid arthritis and it seems to relieve pain and decreases swelling of the joints.


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