Plasmodium vivax relapse prevention — DTM&H MCQ

Correct answer: D — Add primaquine after confirming normal G6PD status

The correct answer is D, add primaquine after confirming normal G6PD status. P. vivax establishes dormant hepatic hypnozoites that are not cleared by blood-stage agents such as chloroquine, so radical cure requires an 8-aminoquinoline (primaquine) to prevent relapse. Because primaquine can precipitate severe oxidative haemolysis in G6PD-deficient patients, UK malaria treatment guidelines mandate that G6PD activity be measured before primaquine is given, with therapy only started once deficiency has been excluded (or managed with modified dosing under specialist supervision if deficiency is confirmed). This patient has already had effective blood-stage treatment with chloroquine; the outstanding requirement is anti-relapse therapy, which must wait for the pending G6PD result rather than being given empirically. Why the other options are wrong: E. Mefloquine weekly for radical cure: Mefloquine is a blood-stage schizonticide with no activity against hepatic hypnozoites, so it cannot achieve radical cure regardless of dosing schedule. A. Doxycycline after fever settles: Doxycycline has no hypnozoiticidal activity and is not used for vivax radical cure; it is reserved for prophylaxis or as a partner drug in other contexts, not for eliminating liver-stage parasites. C. Artesunate alone for hepatic hypnozoites: Artemisinins act rapidly on blood-stage parasites but have no effect on dormant liver hypnozoites, so artesunate cannot substitute for an 8-aminoquinoline. B. Primaquine immediately without enzyme testing: Giving primaquine before G6PD status is known risks life-threatening acute haemolysis in a deficient patient; testing must precede treatment even though it delays radical cure. Key point: Radical cure of P. vivax always needs primaquine to eradicate hepatic hypnozoites, but only after G6PD deficiency has been excluded because of the haemolysis risk.

Reference: UK Malaria Treatment Guidelines Writing Group, Journal of Infection 2016 (PHE/UKHSA endorsed): G6PD activity should be measured before primaquine is given for radical cure of P. vivax or P. ovale malaria, https://www.journalofinfection.com/article/S0163-4453(16)00047-5/fulltext