repeated measurements - ANOVA, friedmann's test or kruskal wallis?

Dear all,

I am a junior doctor getting involved in medical statistics, of which my knowledge is very preliminary.

The problem I face is the following:

I want to analyse the effect of a treatment over time, in a group of patients.

The medication was started at time 0 and I have repeated measurements of a hormone (PTH) and other factors which I want to analyse independently from time 0 every 6 months and up to 5 years.

In the same way I want to analyse the mean dose over time, to see if the patients had an increase in dose. I am not interested to examine how each dose increment affected the results. I just want to examine those factors over time.

Performing a shapiro-wilk test showed that the data are not normally distributed.

Which is the best way to perform this analysis?? Is it Friedman's test? Is it Kruskal-Wallis? Or should I use ANOVA?

Finally, there is a problem with missing values, as only a fraction of patients continued treatment after 3 years. How should I manage this? eg. 50 patients at time 0,6,12,24.. but 18 patients from 36 to 60 months. Should I analyse this subgroup separately?

Thank you for your help, I am grateful.