Proguanil is metabolised in the liver to the active
metabolite, cycloguanil, and to p-chlorophenylbiguanide
which is inactive, mainly by cytochrome P450, CYP
2C19 and slightly by CYP 3A4. Unlike proguanil and
p-chlorophenylbiguanide, cycloguanil is not concentrated
in erythrocytes so concentrations of cycloguanil in
plasma and whole blood are similar. About 40-60% of
a dose of proguanil is excreted in the urine, 60% of this
as the unchanged drug, 30% as cycloguanil, and 8% as
p-chlorophenylbiguanide. About 10% of a dose is excreted
in the faeces.
