How it's calculated
Each drug has a standard lead time before entering the malaria-risk area (to build up drug levels and, for mefloquine, to check tolerability) and a tail period after leaving (to cover the parasite's liver-stage development). The scheduler applies the standard lead/tail times for the selected drug to the given travel dates.
Standard lead/tail times by drug
| Drug | Start before travel | Continue after leaving | Frequency |
|---|---|---|---|
| Atovaquone-proguanil | 1-2 days | 7 days | Once daily |
| Doxycycline | 1-2 days | 4 weeks | Once daily |
| Mefloquine | 2-3 weeks | 4 weeks | Once weekly |
| Chloroquine | 1-2 weeks | 4 weeks | Once weekly |
Clinical use
- Drug choice depends on the destination's resistance patterns, trip length, cost, side-effect profile, and the traveller's contraindications (e.g. mefloquine is avoided with a history of seizures or certain psychiatric conditions; doxycycline causes photosensitivity and isn't used in young children or pregnancy).
- Mefloquine's longer lead-in time before travel is deliberate — it allows any neuropsychiatric side effects to emerge and an alternative to be chosen before departure.
- No chemoprophylaxis regimen is 100% protective — bite-prevention measures (repellent, long sleeves, treated bed nets) remain essential alongside medication.
Frequently asked questions
Why do the drugs have different tail periods after travel?
The tail period needs to cover the liver stage of the malaria parasite's life cycle. Atovaquone-proguanil acts on both liver and blood stages, allowing a shorter 7-day tail; the others act mainly on the blood stage and need a longer 4-week tail to cover parasites still emerging from the liver.
Why does mefloquine need to start 2-3 weeks before travel?
Starting early lets any neuropsychiatric or other side effects appear while there's still time to switch to an alternative drug before departure, and it allows steady-state drug levels to build up.
Is chloroquine still useful for malaria prevention?
Only in the relatively few remaining areas where the local Plasmodium species has not developed chloroquine resistance — most malaria-endemic regions now require an alternative drug. Always confirm current resistance patterns for the specific destination.
References
- CDC Yellow Book — Malaria chapter, chemoprophylaxis regimens.
- WHO. International Travel and Health — Malaria.