metaboliteAny substance involved in a
metabolic reaction (a biochemical reac-
tion in the body). The term metabolite
is sometimes used to refer only to the
products of a metabolic reaction. (See
also metabolism.)
metacarpal boneOne of 5 long, cylin-
drical bones within the hand. The bones
run from the wrist to the base of each
digit, with the heads of the bones form-
ing the knuckles.
metaplasiaA change in tissue resulting
from the transformation of one type of
cell into another. Usually harmless, but
occasionally precancerous, metaplasia
can affect the lining of various organs,
such as the bronchi (airways) and blad-
der. Metaplasia of the cervix, which
occurs in cervical erosion, can be detec-
ted by a cervical smear test.
metastasisA secondary cancerous tu-
mour (one that has spread from a
primary cancerto another part of the
body). The term also applies to the pro-
cess by which such spread occurs.
Metastases can spread through the lym-
phatic system, in the bloodstream, or
across a body cavity.
metatarsal boneOne of 5 long, cylin-
drical bones within the foot. The bones
make up the central skeleton of the foot
and are held in an arch by the surround-
ing ligaments.
metatarsalgiaPain in the foot. Causes
include fracture of a metatarsal bone, flat-
feet, or neuromaof a nerve in the foot.
metatarsophalangeal jointThe joint
between each metatarsal boneand its
adjoining toe bone (see phalanges). The
metatarsophalangeal joint at the base
of the big toe is commonly affected by
goutand by hallux rigidus.
metforminAn oral hypoglycaemic drug
(see hypoglycaemics, oral) that lowers
blood glucose levels and is used to
treat type 2 diabetes mellitus. Possible
adverse effects include loss of appetite, a
metallictaste in the mouth, nausea,
vomiting, and diarrhoea.
methadoneA synthetic opioid analg-
esic drug that resembles morphine.
Methadone is used under supervision
to relieve withdrawal symptoms in peo-
ple undergoing a heroin or morphine
detoxification programme. Side effects
may include nausea, vomiting, consti-
pation, dizziness, and dry mouth.
methaneA colourless, odourless, highly
inflammable gas that occurs naturally
in oil wells and coal mines. Methane is
also produced by the decomposition of
organic matter; it is one of the gases
present in intestinal gas (see flatus).
methanolA poisonous type of alcohol
that is used as a solvent or paint re-
mover and in some types of antifreeze.
Methanol poisoning usually occurs as a
result of drinking it as a substitute for
ordinary alcohol. Symptoms of poison-
ing include headache, dizziness, nausea,
vomiting, and unconsciousness. Dam-
age may also occur to the retinaand the
optic nerve, causing blurred vision. Re-
peated or large doses of methanol may
result in permanent blindness.
methicillin-resistant staphylococcus
aureusSee MRSA.
methotrexateAn anticancer drugused
to treat lymphoma(cancer of the lymph
nodes) and some forms of leukaemia.
Methotrexate is also used to treat can-
cers of the uterus, breast, ovary, lung,
bladder, and testis, and severe psoriasis
when other treatments are ineffective.
Methotrexate may cause nausea, vomit-
ing, diarrhoea, mouth ulcers, anaemia,
increased susceptibility to infection,
and abnormal bleeding.
methyl alcoholAn alternative name
for methanol.
methylcelluloseA bulk-forming laxative
drugused to treat constipation, irritable
bowel syndrome, and diverticular disease.
Methylcellulose increases the firmness
of faeces in chronic watery diarrhoea
and regulates their consistency in peo-
ple who have a colostomyor ileostomy.
It is also given as eyedrops to relieve
dry eyes. As methylcellulose causes a
feeling of fullness, it is sometimes used
to help treat obesity.
methyldopaAn antihypertensive drug.
Adverse effects include drowsiness,
depression, and nasal congestion.
methylenedioxymethamfetamineSee
Ecstasy.
methylphenidateA central nervous
system stimulant drugused, under spe-
cialist supervision, to treat attention
deficit hyperactivity disorder (ADHD)inMETABOLITE METHYLPHENIDATE
M