With GERD or reflux babies you have to feed smaller amounts, but more often. Full bellies for these kids is miserable, as their systems are too slow in digesting.
Right after a bottle, be sure to burp them adequately, and that they are seated upright for about half an hour or so. Use a bouncy chair or swing (don't turn it on or use a very slow setting..too much movement isn't good either), NOT a car seat as children can be susceptible to suffocation if left unattended for long periods in carseats because of the way they can slump down in them.
And if I remember correctly, it seems like my ped said to be sure to give the medicine before they eat not after so the medicine had to time to work. Unlike antacids etc. if the baby is on something like liquid/suspension Zantac, the effects of the drug is cummulative and that if skipped or not properly spaced between meals wouldn't be effective.
Check out www.askdrsears.com or read "Fussy Baby Book" by doctor Sears on the topic of reflux and spit up. The FBB is jam packed with more tips and information on children with GERD and feeding etc. You can do a search on the site for the same info...type in GERD and spit up or feedings.
http://patient-health-education.suite101.com/article.cfm/...
http://www.parenthood.com/article-topics/gerd_beyond_spit...