Webster's New World Medical Dictionary

antibody, antinuclear
See 
antinuclear antibody.
anticholinergic
Opposing the actions of the neu-
rotransmitter acetylcholine. Anticholinergic drugs
inhibit the transmission of parasympathetic nerve
impulses, thereby reducing spasms of smooth mus-
cles (for example, muscles in the bladder). Side
effects of anticholinergic medications include dry
mouth and related dental problems, blurred vision,
tendency toward overheating (hyperpyrexia), and in
some cases, dementia-like symptoms.
anterior pituitary
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anticipation
The progressively earlier appear-
ance and increased severity of a disease from gen-
eration to generation. The phenomenon of
anticipation was once thought to be an artifact, but
a biological basis for it has been discovered in a
number of genetic disorders, such as myotonic dys-
trophy and Huntington disease.
anti-citrulline antibody
See 
citrulline anti-
body.
anticoagulant
An agent that is used to prevent the
formation of blood clots. Anticoagulants have vari-
ous uses. Some are used for the prevention or treat-
ment of disorders characterized by abnormal blood
clots and emboli. Anticoagulant drugs include intra-
venous heparin, which acts by inactivating thrombin
and several other clotting factors that are required
for a clot to form, and oral anticoagulants such as
warfarin and dicumarol, which act by inhibiting the
liver’s production of vitamin K–dependent factors
that are crucial to clotting. Anticoagulant solutions
are also used for the preservation of stored whole
blood and blood fractions and to keep laboratory
blood specimens from clotting.
antidepressant
A medication that prevents or
reduces the symptoms of clinical depression. Some
antidepressants may also be prescribed for their
other medical effects, including increasing blood
flow within the brain and treating chronic pain. See
also 
MAO inhibitor; SSRI; tricyclic antidepressant.