Across from = opposite So 'from' is used with across but not with opposite Across from is little used in British English. It's more an American English term while opposite is used more in British English.

Both opposite and across CAN be followed by 'from'. across vs across from If there is an obstacle between the 2 mentioned points you can use 'from' e.g - The school is across from the bank. ( the bank is the obstacle - you have to go around it to reach your destination. - The school is across the street. ( no obstacle - you can cross the street and go to your destination - so the word 'from' is not required.) opposite vs opposite from When opposite is used as an adjective it can be followed by from. e.g - The school is on the opposite side from our house. - The school is opposite our house. (not followed by a noun so its a preposition here - no need to use from) so your example should be kept as it is ... opposite the pharmacy / across from the pharmacy

Yes you could use "from" in your example. For this example of giving the directions to to a location, "across from" sounds a little more natural to me. "from" is used to imply that the travel agent is across/opposite FROM THE LOCATION of the pharmacy. Hope this helps!