Medicine/Medical. immediate, temporary immunization against the effects of injection of a toxic extract owing to previous small injections of the same extract.
a decreased response to a medicine given over a period of time so that larger doses are required to produce the same response.
Also, tachyphylaxia [tak-uh-fi-lak-see-uh] .

tachy- + Greek phýlaxis a guarding, equivalent to phylak- (stem of phylássein to guard) + -sis -sis

tachyphylactic [tak-uh-fi-lak-tik] , adjective
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World English Dictionary
tachyphylaxis (ˌtækɪfɪˈlæksɪs)
very rapid development of tolerance or immunity to the effects of a drug
[New Latin, from tachy- + phylaxis on the model of prophylaxis. See prophylactic]

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American Heritage
Medical Dictionary

tachyphylaxis tach·y·phy·lax·is (tāk'ə-fĭ-lāk'sĭs)

  1. Rapid desensitization to a pharmacologically or physiologically active substance produced by inoculation with a series of small doses.

  2. A rapidly decreasing response to a drug following its initial administration.

The American Heritage® Stedman's Medical Dictionary
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