SSRI vs fluoxetine

SSRI and fluoxetine both are nouns.

Word	Noun	Adjective	Verb	Adverb
SSRI	Yes	No	No	No
fluoxetine	Yes	No	No	No

As nouns, fluoxetine is a hyponym of SSRI; that is, fluoxetine is a word with a more specific, narrower meaning than SSRI:

SSRI: an antidepressant drug that acts by blocking the reuptake of serotonin so that more serotonin is available to act on receptors in the brain
fluoxetine: a selective-serotonin reuptake inhibitor commonly prescribed as an antidepressant (trade names Prozac or Sarafem); it is thought to work by increasing the activity of serotonin in the brain

Other hyponyms of SSRI include fluoxetine hydrocholoride, Prozac, Sarafem, paroxetine, Paxil, sertraline, Zoloft.

SSRI (noun)	fluoxetine (noun)
an antidepressant drug that acts by blocking the reuptake of serotonin so that more serotonin is available to act on receptors in the brain	a selective-serotonin reuptake inhibitor commonly prescribed as an antidepressant (trade names Prozac or Sarafem); it is thought to work by increasing the activity of serotonin in the brain