well, this is not kansas
the meds sold in DR are made mostly in south america by SA companies. there are few labs brought from USA or europe including the medicine you may know already, but sold here under different brand names.
antigripal:
there is tabcin here. both in effervescent tablets and in liquid gel capsules. no theraflu anymore but there is sinutab or winasorb in tea and in pills. just ask for anything for gripe, it will be roughly the same crap you already know. the compounds are similar in most products.
zantac is ranitidina, normally sold here in 300mg version, somewhat 150mg does not appeal to dominicans
8 pesos per pill.
prilosec is omeprazole, in the form of 20 or 40mg pill. 6 pesos for 20mg and 25 pesos for 40mg.
before you set off to buy anything google it and check the main compound. ask for that specifically, not for a brand.