Biology Reference
In-Depth Information
malaria which have the potential to reduce total parasitaemia
.
The first
is eradication of blood-stage parasites, the second is post-treatment pro-
phylaxis against recurrent blood-stage infection and the third is preven-
tion of future relapses using hypnozoitocidal drugs. We consider these
separately.
3.1. Eradicating Blood-Stage Parasites
Interrupting acute
P. vivax
infections is possible using a range of differ-
ent anti-malarial drugs. All drugs that are commonly used for falciparum
malaria are active against both the asexual and sexual stages of
P. vivax
but
there is significant variability in their potency (
Pukrittayakamee et al., 2004
,
2008
). In the absence of acquired resistance, the artemisinin derivatives
have the highest potency followed by chloroquine, the other quinolines
(including mefloquine, quinine and primaquine), the anti-bacterial anti-
malarials clindamycin, tetracycline, doxycycline and azithromycin followed
by sulfadoxine + pyrimethamine (SP) (
Pukrittayakamee et al., 2004
;
Darlow
et al., 1982
). The potencies of the ACT partner drugs, lumefantrine and
piperaquine, have not been compared head-to-head with the aforemen-
tioned anti-malarials
in vivo
but
in vitro
experiments suggest that they fall
below chloroquine but well above the antibiotic anti-malarials (
Lux et al.,
2003, 2011
;
Chotivanich et al., 2009
).
In vitro
studies in Papua, Indonesia,
an area endemic for chloroquine-resistant
P. vivax
, demonstrate that the
potency of amodiaquine is similar to lumefantrine and piperaquine (
Russell
et al., 2008
).
In vitro
and
in vivo
evidence suggests that development of chlo-
roquine resistance confers cross-resistance to amodiaquine (
Hasugian et al.,
2007
,
2009
;
Russell et al., 2008
).
Drugs with greater potency clear asexual parasitaemia, and therefore,
gametocytaemia, faster than drugs with lower potency. However, the rela-
tive transmission-blocking benefits of more rapid clearance alone will be
minimal since gametocytes capable of transmission will almost certainly
have been present in the peripheral circulation for a number of days prior
to presentation (
Huh et al., 2011
;
Ratcliff et al., 2007
;
Hasugian et al., 2007
).
Furthermore, assuming complete parasitological cure, the majority of para-
sitaemia associated with a single inoculation is likely to be related to relapses
rather than the primary episode (
Hill and Amatuzio, 1949
;
Hankey et al.,
1953
). Apart from primaquine, none of the blood schizontocides used for
the treatment of vivax malaria has activity against hypnozoites and, there-
fore, cannot eliminate the potential for future relapses. A 1-week course
of 60 mg primaquine daily will clear blood-stage
P. vivax
parasitaemia
