Monograph: |
Histamine
Hygroscopic, colourless crystals or white crystalline powder.
Histamine hydrochloride 1.66 mg is approximately equiva-
lent to 1 mg of histamine. Very soluble in water: soluble in
alcohol; practically insoluble in ether. A 5% solution in water
has a pH of 2.85 to 3.60. Protect from light.
Stability. A study concluded that solutions of histamine
phosphate could be sterilised by heating in an autoclave with
little degradation. Autoclaved solutions could be stored for a
minimum of 4 months.
Adverse Effects and Treatment
injection of histamine salts can produce a range of adverse
effects that includes headache, flushing of the skin. general
vasodilatation with a fall in blood pressure, tachycardia, bron-
chial constriction and dyspnoea, visual disturbances, vomit-
ing, diarrhoea, and other gastro-intestinal effects. These
reactions may be serious and excessive dosage can produce
collapse and shock, and may be fatal. Reactions may occur at
the injection site.
Some of these effects may be relieved by an antihistamine.
but adrenaline may be required and should always be availa-
ble.
Precautions
Histamine salts should be used with care in patients with asth-
ma or other hypersensitivity disorders, in elderly patients, and
in patients with cardiovascular disorders.
Pharmacokinetics
Histamine salts exert a rapid, though transient, effect when
given parenterally. Histamine is rapidly metabolised by meth-
ylation and oxidation: the metabolites are excreted in the
urine.
Uses and Administration
Histamine causes stimulation of smooth muscle, especially of
the bronchioles, and lowers blood pressure by dilating the ar-
terioles and capillaries. It also stimulates exocrine gland se-
cretion, especially the gastric glands.
Intradermal injection of histamine produces the characteristic
'triple response' of erythema, flare, and wheal. This is utilised
as a control response in skin testing for hypersensitivity. Also,
since it is mediated in part by axon reflexes, it has been used
to test the integrity of sensory nerves, for example in leprosy.
)
Inhalation of histamine causes bronchoconstriction and is
used as a test of bronchial reactivity.
Histamine has also been given subcutaneously to identify the
causes of achlorhydria and intravenously in the diagnosis of
phaeochromocytoma. but safer tests are generally preferred.
Histamine is included in some combination topical preparations
For musculoskeletal disorders.
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