Averaging and comparing mean values across studies

#1
I am having a statistical problem that falls into two parts:

(!) I have several literature reports on studies that have investigated the effect of drug "A" on a particular laboratory parameter. Some articles report the mean and SD values at baseline and treatment end while others report mean and SD intra-individual change between baseline and end of treatment. How can I determine the average change between baseline and treatment end across all studies?

(2) Experiments like those in (1) have been reported not only for drug "A", but also for "B", "C", and "D" (of course, the laboratory measure of interest is always the same). For each drug, I only have some value(s) for average change over time, but there is neither a head-to-head comparison nor an indirect comparison between them. Is there anything more that I can do to compare the effects of the drugs on the lab measure except to present average change and some measure of variability side by side?

Thank you,
Andreas