Encyclopedia of Health and Medicine

248 The Immune System and Allergies
sea center. Antihistamine medications with H3
blocking capability thus cause drowsiness and
relieve nausea as well. Second-generation antihistamine
medications are selective. They block primarily
H1 receptors and have little effect on H3
receptors; thus they do not generally cause
drowsiness and provide little or no relief of nausea.
Third-generation antihistamine medications
derive from second-generation antihistamines and
are purported to have fewer side effects and
adverse reactions though functionally are no different.
Many antihistamine medications are available
in the United States as OVER-THE-COUNTER
(OTC) DRUGS, sometimes in combination with a
decongestant or other ingredients. Manufacturers
often market OTC antihistamines as allergy-relief
products. Other antihistamines require a doctor’s
prescription.
ANTIHISTAMINE MEDICATIONS
First-Generation (Nonselective) Antihistamines
brompheniramine
chlorpheniramine
dexchlorpheniramine
dimenhydrinate
diphenhydramine
doxylamine
hydroxyzine
phenindamine
pheniramine
pyrilamine
triprolidine
Second-Generation (Selective H1) Antihistamines
acrivastine
azatadine
cetirizine
clemastine
cyproheptadine
loratadine
mizolastine
Third-Generation (Selective H1) Antihistamines
desloratadine
fexofenadine
levocetirizine
Therapeutic Applications
Doctors prescribe or recommend antihistamine
medications to treat ALLERGIC RHINITIS, ALLERGIC
CONJUNCTIVITIS, and ALLERGIC DERMATITIS. Most of the
nonselective antihistamines cause significant
drowsiness; doctors prescribe or recommend them
for intermittent insomnia (difficulty sleeping).
Meclizine is an H3 receptor antihistamine effective
for nausea and VOMITING, especially that associated
with motion sickness. Meclizine has little effect on
H1 receptors, however, so does not influence the
immune response or relieve symptoms of hypersensitivity
reaction.
Some antihistamine medications have other
therapeutic applications, such as
• anxiety: hydroxyzine
• sedative and sleep aid: diphenhydramine,
doxylamine, hydroxyzine
• nausea and vomiting: dimenhydrinate, diphenhydramine,
hydroxyzine
• VERTIGO: dimenhydrinate, diphenhydramine
• early PARKINSON’S DISEASE: diphenhydramine
Risks and Side Effects
In general antihistamine medications cause few
side effects other than drowsiness, although can
raise BLOOD PRESSURE. People who take other medications
to treat chronic health conditions should
check with their doctors before taking antihistamines,
as antihistamines can exacerbate symptoms
or interfere with the actions of other drugs.
See also ANTIBODY; ARTERY; CORTICOSTEROID MED-
ICATIONS; CAPILLARY BEDS; GENERALIZED ANXIETY DISOR-
DER (GAD); H2 ANTAGONIST (BLOCKER) MEDICATIONS;
LIVING WITH ALLERGIES; LYMPHOCYTE; NEUROTRANSMIT-
TER; PROTON PUMP INHIBITOR MEDICATIONS; SNEEZE.
antimitochondrial antibodies Autoantibodies
the IMMUNE SYSTEM produces that attack the mitochondria
within self cells. Mitochondria are the
organelles (functional structures) within a cell that
generate the energy the cell needs to carry out its
activities. Antimitochondrial antibodies are proteins
that bind with antigens (other proteins) on
the inner walls of the mitochondria, blocking the
ability of the mitochondria to convert oxygen to
energy. The cell dies as a result.
CONDITIONS IN WHICH
ANTIMITOCHONDRIAL ANTIBODIES ARE PRESENT
CIRRHOSIS
PRIMARY SCLEROSING CHOLANGITIS
SYSTEMIC LUPUS ERYTHEMATOSUS (SLE)
PRIMARY BILIARY CIRRHOSIS
RHEUMATOID ARTHRITIS
THYROIDITIS
A BLOOD test called the antimitochondrial ANTI-
BODY (AMA) titer detects and measures antimitochondrial
antibodies in the blood circulation. Their
presence indicates various AUTOIMMUNE DISORDERS,
notably PRIMARY BILIARY CIRRHOSIS and PRIMARY SCLE-