The word antiserum is playable in Words With Friends™, no blanks required. Because it is longer than 7 letters, you would have to play off an existing word or do it in several moves.
Words With Friends™ Letter Score: 14
Highest Scoring Words With Friends™ Play In The Letters
Seven Letter Word Alert: (44 words)
antsier, arenium, artsmen, atriums, aunties, inmates, manures, marines, martens, martins, matures, minaret, minters, minuets, minuter, minutes, mistune, misturn, munites, muriate, mustier, nastier, natures, nutsier, raiment, remains, remints, restain, retains, retinas, runtime, saunter, seminar, sinuate, sirname, smarten, smartie, stainer, sternum, surname, tsunami, uniters, unmates, urinate