Pure phonetic transliteration of 'prednisone' —
强 (qiáng, 'pred-'),
的 (de, '-ni-'),
松 (sōng, '-sone'). The characters' lexical meanings ('strong's pine') are irrelevant; treat it as a fixed pharmacological name. Modern Chinese also uses the calque
泼尼松 (pōnísōng).