oxygen in body tissues). The oxygen is
usually delivered through a face-mask or
a nasal cannula (a length of narrow plas-
tic tubing with two prongs that are
inserted into the nostrils). Piped oxygen
is used in hospitals; oxygen in cylinders
can be used at home for acute attacks
of hypoxia, such as those occurring in
severe asthma. Long-term therapy for
people with persistent hypoxia may in-
volve the use of an oxygen concentrator.
(See also hyperbaric oxygen treatment.)
oxymetazolineA decongestant drug
used in the treatment of allergic rhinitis,
sinusitis, and the common cold.
oxytetracyclineA tetracycline antibiotic
drugthat is used to treat chlamydial in-
fectionssuch as nongonococcal urethritis.
It is also used for a variety of other
infective conditions, including bronchi-
tisand pneumonia; in addition, the drug
may be used to treat severe acne.
Side effects may include nausea, vom-
iting, diarrhoea, skin rash, and increased
sensitivity of the skin to sunlight. Oxy-
tetracycline may discolour developing
teeth, and is not given to children under
12 or to pregnant women.
oxytocinA hormoneproduced by the
pituitary gland. Oxytocin causes uterine
contractionsduring labour and stimulates
milk-flow in breast-feedingwomen.
Synthetic oxytocin is used for induc-
tion of labour. It is given by intravenous
infusion to produce uterine contractions.
It is also often given with ergotamine as
a single dose after delivery to prompt
placental separation and expulsion, to
reduce blood flow, or to empty the
uterus after an incomplete miscarriage
or a fetal death. A possible adverse
effect of synthetic oxytocin is abnorm-
ally strong, painful contractions. Rare
side effects include nausea, vomiting,
palpitations, and allergic reactions.
oxyuriasisAn alternative name for
enterobiasis orthreadworm infestation.
ozenaA severe and rare form of rhinitis,
in which the mucus membrane in the
nose wastes away and a thick nasal dis-
charge dries to form crusts. Ozena often
causes severe halitosis.
ozoneA rare form of oxygen, ozone is a
poisonous, faintly blue gas that is pro-
duced by the action of electrical
discharges (such as lightning) on oxy-
gen molecules. Ozone occurs naturally
in the upper atmosphere, where it
screens the Earth from most of the
Sun’s harmful ultraviolet radiation. The
ozone layer is being depleted by atmo-
spheric pollutants, allowing increasing
amounts of ultraviolet radiation to
reach the Earth’s surface. This problem
could lead to a rise in the incidence of
skin cancer and cataracts, as well as hav-
ing other potentially hazardous effects.OXYMETAZOLINE OZONE
O