Is this what you want?
local config = {
summonName = "Troll",
isNPC = false
}
function onUse(cid, item, fromPosition, itemEx, toPosition)
if isNPC then
doCreateNpc(config.summonName, getCreaturePosition(cid))
elseif getTilePzInfo(getCreaturePosition(cid)) == 0 then...