Rogueclassicism wonders if there was any ancient wine known as Guaranum
with medicinal properties. It's probably just a typo for Gauranum, the wine from vines on Mount Gaurus (today Monte Gauro) in Campania. See Pliny, Natural History
14.8.64 (tr. John Bostock and H.T. Riley):
To the third rank belonged the various wines of Alba, in the vicinity of the City, remarkable for their sweetness, and sometimes, though rarely, rough as well: the Surrentine wines, also, the growth of only stayed vines, which are especially recommended to invalids for their thinness and their wholesomeness. Tiberius Caesar used to say that the physicians had conspired thus to dignify the Surrentinum, which was, in fact, only another name for generous vinegar; while Caius Caesar, who succeeded him, gave it the name of "noble vappa." Vying in reputation with these are the Massic wines, from the spots which look from Mount Gaurus towards Puteoli and Baiae.
At tertiam palmam varie Albana urbi vicina, praedulcia ac rara in austero, item Surrentina in vineis tantum nascentia, convalescentibus maxime probata propter tenuitatem salubritatemque. Tiberius Caesar dicebat consensisse medicos ut nobilitatem Surrentino darent; alioqui esse generosum acetum; C. Caesar, qui successit illi, nobilem vappam. certant Massica atque a monte Gauro Puteolos Baiasque prospectantia.