to prevent and treat epileptic fits (see
epilepsy). It also prevents petit malattacks
in children. Side effects include drowsi-
ness, dizziness, fatigue, and irritability.
cloneAn exact copy. In medicine, the
term usually refers to copies of cells,
genes, or organisms. Clones of cells are
all descended from one original cell. In
many types of cancer, cells are thought
to be derived from one abnormal cell.
Clones of genes are duplicates of a sin-
gle gene. In research, several copies of a
gene can be made to enable the gene to
be studied in detail. Clones of organ-
isms are produced by removing the
nuclei from cells of a donor individual
and transplanting them into the egg
cells of another individual. When the
eggs mature into living plants or ani-
mals, they are all identical to the donor.
clonidineAn antihypertensive drug used
to reduce high blood pressure. Possible
side effects include drowsiness, dizziness,
dry mouth, and constipation. Abrupt
withdrawal of high doses can cause a
dangerous rise in blood pressure.
clonusA rapid series of abnormal mus-
clecontractions that occur in response
to stretching. Clonus is a sign of dam-
age to nerve fibres that carry impulses
from the motor cortex in the cerebrum
to a particular muscle. It is also a fea-
ture of seizures in grand mal epilepsy.
clostridiumAny of a group of rod-
shaped bacteria. Clostridia are found in
soil and in the gastrointestinal tracts of
humans and animals. They produce
powerful toxins and are responsible for
potentially life-threatening diseases
such as botulism, tetanus, and gangrene.
clotrimazoleA drug used to treat yeast
and fungal infections, especially can-
didiasis(see antifungal drugs).
clove oilAn oil distilled from the dried
flower-buds of EUGENIA CARYOPHYLLUS,
used mainly as a flavouring in pharma-
ceuticals. Clove oil is sometimes used
to relieve abdominal pain due to flatu-
lenceand as a remedy for toothache.
cloxacillinA penicillin-type antibiotic
used to treat infections with staphylo-
coccal bacteria (see penicillin drugs).
clubbingThickening and broadening of
the tips of the fingers and toes, usually
with increased curving of the nails. It is
associated with chronic lungdiseases,
such as lung cancer, bronchiectasis, and
fibrosing alveolitis; with certain heart
abnormalities;and, occasionally, with
Crohn’s diseaseand ulcerative colitis.
club-footA deformity of the foot, pre-
sent from birth (see talipes).
cluster headachesBrief but severe
headaches that recur up to several times
a day over a few days. Cluster head-
aches affect one side of the head or
face. The cause is uncertain but they
may be due to dilation of blood vessels
in the brain as in migraine. Beta-blocker
drugsmay be given to reduce the sever-
ity and frequency of cluster headaches.
CNSAn abbreviation for central nervous
system (the brain and spinal cord).
CNS stimulantsDrugs that increase
mental alertness (see stimulant drugs).
coagulation, bloodThe main mecha-
nism by which blood clots are formed,
involving a complex series of reactions
in the blood plasma(see blood clotting).
coal tarA thick, black, sticky substance
distilled from coal. It is a common
ingredient of ointments and medicinal
shampoos prescribed for skin and scalp
conditions such as psoriasisand some
forms of dermatitisand eczema.
co-amoxiclavA penicillin drugcontaining
a mixture of amoxicillinand clavulanic acid.
Because it is a more powerful antibiotic
than amoxicillin alone, co-amoxiclav is
used to treat infections caused by
amoxicillin-resistant strains of bacteria.
coarctation of the aortaA congenital
heart defect of unknown cause, in which
there is narrowing in a section of the
aortathat supplies blood to the lower
body and legs. In response, the heart
has to work harder, causing hyperten-
sionin the upper part of the body.
Symptoms usually appear in early child-
hood and include headache, weakness
after exercise, cold legs, and, rarely,
breathing difficulty and swelling of the
legs due to heart failure. Associated
abnormalities include a heart murmur,
weak or absent pulse in the groin, lack
of synchronization between groin and
wrist pulses, and higher blood pressure
in the arms than in the legs. X-rays con-
firm the diagnosis. Corrective surgery is
usually performed at 4–8 years of age.CLONE COARCTATION OF THE AORTA
C