Table 2.

Radical treatment pharmacodynamics; Quantitative considerations

Consider two groups of patients who represent two extremes
Without radical treatment group A has an 80% relapse rate (eg some soldiers who fought in the Pacific in the Second World War)
Without radical treatment group B has a 20% relapse rate (eg some soldiers who fought in the Korean War)
Assuming a fixed fractional proportion of relapses and no acquisition of immunity, then the total number of relapses/100 patients is
group A = 395,	group B = 24.
These numbers represent the minimum number of viable activatable hypnozoites (VAH) i.e. there are 16 times more in group A compared to group B. It is likely that the distribution of VAH is random among the patients and therefore conforms to a Poisson distribution.
If primaquine at a dose of 0.25 mg base/kg (15 mg adult dose) reduces the number of viable activatable hypnozoites (VAH) by 90%, and there is no difference in susceptibility between the groups, and this effect is consistent across all patients then the post treatment number of VAH is
group A = 39 or 40	group B = 2 or 3.
Thus we would expect 13 to 20 times more relapses in group A compared to group B.
This hypothetical example simply points out that the apparent differences in primaquine "resistance" may reflect differences in the biology of the parasite rather than drug susceptibility per se.