treatment with antibiotic drugsand, in
some cases, possibly plastic surgery.
Good nursing care, including changing
the patient’s position regularly, skin
care, protection of vulnerable areas,
and use of cushions and special mat-
tresses, should prevent pressure sores
from developing in most cases.
prevalenceThe total number of cases
of a disease at any one time in a
defined population. Prevalence is often
expressed as the number of cases per
100,000 people.
preventive dentistryAn aspect of den-
tistry concerned with the prevention of
tooth decay and gum disease. It consists
of the encouragement of good oral
hygiene, fluoridetreatment, and scaling.
preventive medicineThe branch of
medicine that deals with the prevention
of disease by public health measures,
such as the provision of pure water sup-
plies; by health education; by specific
preventive measures, such as immu-
nizationagainst infectious diseases; and
by screening programmes to detect dis-
eases before they cause symptoms.
priapismPersistent, painful erectionof
the peniswithout sexual arousal. Pri-
apism occurs when blood does not
drain from the spongy tissue of the
penis, thus keeping the penis erect. This
may be caused by clotting in the blood
vessels due to a blood disorder or as a
result of treatment for impotence. Urgent
treatment is needed in order to avoid
permanent damage. The treatment may
involve withdrawal of blood from the
penis with a needle.
prickly heatAn irritating skin rash that
is associated with profuse sweating.
The medical name is miliaria rubra.
Multiple tiny, red, itchy spots cover the
affected areas of skin and are accompa-
nied by prickling sensations. The irri-
tation tends to affect areas where sweat
collects, such as the armpits. The cause
is not fully known, but unevaporated
sweat is an important factor. Sweat
ducts become blocked with debris and
leak sweat into the skin. Frequent cool
showers and sponging of the affected
areas relieve the itching.
primaquineA drug used to treat vivax
and ovale malaria. It is often given afterprophylactic treatment with chloroquine
has failed to prevent infection.
Adverse effects include nausea, vomit-
ing, and abdominal pain. In people with
G6PD deficiency, primaquine may cause
haemolytic anaemia.
primaryA term applied to a disease
that has originated within the organ or
tissue affected, and is not derived from
any other cause or source. The term pri-
mary is also applied to the 1st of
several diseases to affect a tissue or
organ in turn. Primary is also used to
mean “of unknown cause”.
primary careHealth care provided by
a general practitioner or other health-
care professional who is the 1st contact
for a patient seeking medical treatment.
primary teethThe 1st teeth (also known
as milk teeth), which usually start to
appear at age 6 months and are replaced
by the permanent teethfrom about age
6 years. There are 20 primary teeth, 10
in each jaw. (See also teeth; eruption of
teeth; teething.)
primidoneAn anticonvulsant drug used
to treat epilepsyand, occasionally, tremor.
It is usually prescribed with another
anticonvulsant. Adverse effects include
drowsiness, clumsiness, and dizziness.
Prinzmetal’s anginaSee variant angina.
prionA tiny, protein-based infectious
particle. Prions transmit diseases, includ-
ing Creutzfeldt–Jakob diseasein humans
and bovine spongiform encephalopathy
(BSE)in cattle. Prions do not contain
nucleic acids and are difficult to des-
troy. As yet, no treatment is available
for prion diseases.
PRKThe abbreviation for photorefractive
keratectomy.
probenecidA drug used in the long-
term treatment of gout. Probenecid also
slows the excretion of some antibiotic
drugsand so is occasionally prescribed
with these drugs to boost their levels
and thus their effects. It may cause nau-
sea and vomiting. Other possible
effects include flushing and dizziness.
probiotic bacteriaSpecies of microor-
ganisms that inhabit the digestive tract,
guarding it against harmful bacteria,
yeasts, and viruses.
procainamideAn antiarrhythmic drug
that is used to treat certain types ofPREVALENCE PROCAINAMIDEP