Biology Reference
In-Depth Information
7.1. Tafenoquine
One future possibility is to develop a better 8-aminoquinoline than pri-
maquine. This may already exist in tafenoquine, which is an investiga-
tional, long-acting primaquine analogue that has been already been given
to >2000 persons, mostly Australian soldiers ( Nasveld et al., 2002 ; Shanks
et al., 2001 ; Lell et al., 2000 ). Major benefit is that this high dose may be
possible to administer in a single dose, which would exclude problems of
compliance currently seen with long primaquine dosing schedules. ( Shanks
et al., 2001 ). Tafenoquine has been used in combination with chloroquine
to treat acute vivax malaria, to eliminate residual liver parasites to prevent
relapses and as chemoprophylaxis for ongoing exposure in endemic areas
( Shanks et al., 2001 ). There is good laboratory evidence that tafenoquine
will kill parasites in the mosquito ( Ponsa et al., 2003 ). Tafenoquine is not
markedly more efficacious than primaquine, just much easier to administer
which in itself might qualify it for a public health use if there were no ques-
tions about severe adverse events. Tafenoquine, however, is known to cause
haemolysis in G6PD-deficient persons although even severe haemolytic
events have not continued past a single episode despite tafenoquine's long
half-life ( Shanks et al., 2001 ). Currently, studies are underway to discover
if there is an effective dosage or delivery system for tafenoquine that can
be given safely to large populations without screening each individual for
G6PD deficiency.
7.2. Methylene Blue
Methylene blue is a dye that was the earliest synthesized antimalarial drug
having first been tested at the end of the nineteenth century. Used in com-
bination with other medications such as amodiaquine, it has been shown
to be well tolerated and effective for falciparum malaria in African adults
and children ( Bountogo et al., 2010 ; Zoungrana et al., 2008 ; Meissner et al.,
2005 , 2006 ). While conducting these African field trials, methylene blue
was noted to be an excellent gametocide, which has been confirmed in vitro
with falciparum ( Coulibaly et al., 2009 ; Adjalley et al., 2011 ). The ability of
vivax malaria to produce gametocytes from the beginning of blood infec-
tion unlike falciparum, which does not produce sexual stages capable of
mosquito infection for some days to weeks after blood infection is achieved,
indicates that methylene blue might have an anti-transmission indica-
tion for both species. Methylene blue has haemolytic potential in persons
with G6PD but it appears to be less haemolytic than primaquine. As a dye,
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