Suramin
Suramin (Germanin) is a derivative of a nonmetallic dye whose antiparasitic
mechanism of action is not clear. It appears to act on parasite specific
-glyc-erophosphate oxidase, thymidylate synthetase, dihydro-folate reductase,
and protein kinase but not on host en-zymes.
Suramin is not absorbed from
the intestinal tract and is administered intravenously. Although the initial
high plasma levels drop rapidly, suramin binds tightly to and is slowly
released from plasma proteins, and so it persists in the host for up to 3
months. Suramin neither penetrates red blood cells nor enters the CNS. It is
taken up by the reticuloendothelial cells and accumu-lates in the Kupffer cells
of the liver and in the epithe-lial cells of the proximal convoluted tubules of
the kid-ney. It is excreted by glomerular filtration, largely as the intact
molecule.
Suramin is used primarily to
treat African try-panosomiasis, for which it is the drug of choice. It is
ef-fective in treating disease caused by Trypanosoma
gam-biense and T. rhodesiense but
not T. cruzi (Chagas’ disease). It
can be used alone prophylactically or during the initial hemolymphatic stages
of the disease. Later stages, particularly those involving the CNS, are more
commonly treated with a combination of suramin and the arsenical melarsoprol.
When CNS involvement occurs,
the poor penetra-tion of suramin and pentamidine into the CSF requires
alternative forms of chemotherapy, such as melarsoprol in combination with
suramin. In treating Onchocerca volvulus infections, suramin kills adult
worms and is an alternative to
ivermectin. Suramin is used after initial treatment with diethylcarbamazine,
which is used to kill the microfilariae. It produces favorable results in
pem-phigus and prolongs the time to disease progression in hormone-refractory
prostate cancer.
It is important to test for
drug sensitivity by admin-istering a small (200 mg) dose by slow intravenous
in-jection before giving the full amount of suramin. Since adverse reactions
occur with greater frequency and severity among the malnourished, greater
caution is necessary for patients with advanced trypanosomiasis. An acute
reaction in sensitive individuals results in nau-sea, vomiting, colic,
hypotension, urticaria, and even un-consciousness; fortunately, this reaction is
rare. Rashes, photophobia, paresthesias, and hyperesthesia may oc-cur later;
these symptoms may presage peripheral neu-ropathy. Mild albuminuria is not
uncommon, but hema-turia with casts suggests nephrotoxicity and the need to
stop treatment.
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