[R] Paired test for 2-way ANOVA

[A Ezhil]

Hi,

I have an experimental data with 2 factors: visit and treatment. Each subject has 2 visits and on each visit they get a treatment. We take samples before and after treatment. I can easily to do the 2-way ANOVA in R with visit and treatment as factors. 

anova( lm(data ~ visit*treatment) )

If I want to do the same 2-way ANOVA for the paired samples, how can I do that? Is there any R packages for that?

Thanks in advance.

Kind regards,
Ezhil