is a safe, low-cost alternative drug for the treatment of Schistosoma haematobium infections. It is not active against S mansoni or S japonicum. It is not
available in the USA.
an organophosphate compound, is rapidly absorbed after oral administration.
After the standard oral dose, peak blood levels are reached in 1–2 hours; the
half-life is about 1.5 hours. Clearance appears to be through nonenzymatic
transformation to dichlorvos, its active metabolite. Metrifonate and dichlorvos
are well distributed to the tissues and are completely eliminated in 24–48
mode of action is thought to be related to cholinesterase inhibition. This
inhibition temporarily paralyzes the adult worms, resulting in their shift from
the bladder venous plexus to small arterioles of the lungs, where they are
trapped, encased by the immune system, and die. The drug is not effective
against S haematobium eggs; live eggs
continue to pass in the urine forseveral months after all adult worms have been
the treatment of S haematobium, an
oral dose of 7.5–10 mg/kg is given three times at 14-day intervals. Cure rates
on this schedule are 44–93%, with marked reductions in egg counts in those not
cured. Metrifonate was also effective as a prophylactic agent when given
monthly to children in a highly endemic area, and it has been used in mass
treatment programs. In mixed infections with S haematobium and S mansoni,
metrifonate has been successfullycombined with oxamniquine.
Some studies note mild
and transient cholinergic symptoms, including nausea and vomiting, diarrhea,
abdominal pain, bron-chospasm, headache, sweating, fatigue, weakness, dizziness,
and vertigo. These symptoms may begin within 30 minutes and persist up to 12
Metrifonate should not
be used after recent exposure to insec-ticides or drugs that might potentiate
cholinesterase inhibition. Metrifonate is contraindicated in pregnancy.