94 Section 2/ Drugs Acting on CNSAdverse effects include nausea, vomit-
ing, diarrhoea, abdominal pain, neuropathy,
myopathy especially in patients with de-
creased renal function. Prolonged therapy
may lead to aplastic anaemia, agranulocy-
tosis, alopecia and myopathy.
It is used in the treatment of acute gout
and prophylaxis of gout.
ALLOPURINOL
It inhibits the terminal steps in uric acid
biosynthesis by inhibiting enzyme xan-
thine oxidase. During therapy with allopu-
rinol the uric acid plasma levels decline.
After oral intake it is absorbed relatively
rapidly. It is converted to alloxanthine which
is active and non competitive inhibitor.
Adverse effects include hypersensitiv-
ity reactions, maculopapular rash, urticaria,
myalgia, malaise fever, transient leucope-
nia or leukocytosis, hepatic damage, nau-
sea, vomiting, diarrhoea, headache and
drowsiness.
It is indicated in primary hyperuricaemia
of gout, secondary hyperuricaemia due to
myeloid metaplasia, radiation, cancer chemo-
therapy, thiazide diuretics.
PROBENECID
It increases the excretion of uric acid (by
inhibiting its reabsorption from kidney tu-
bules) and hence causes reduced serum lev-
els of uric acid.
After oral administration it is completely
absorbed. It is 90% plasma protein bound. It
is partly metabolised and excreted in urine.
The metabolites also have uricosuric action.
Adverse effects include skin rash,
gastro-intestinal irritation. Overdosage may
result in convulsions and death due to res-
piratory failure.
It is used in chronic gout and secondary
hyperuricaemia.SULFINPYRAZONE
Pyrazolone derivative related to phe-
nylbutazone. It has uricosuric action. It also
inhibits platelet aggregation.
It is well absorbed orally and 98%
plasma protein bound. It is excreted by ac-
tive secretion in proximal renal tubule.
Adverse effects are gastric irritation
(most common), hypersensitivity reactions.
It is used in chronic gout.