Regional selection simulator — вибір хіміопрофілактики малярії за регіоном: matching resistance patterns, trip length, and contraindications to a chemoprophylaxis regimen.
Chloroquine was once the backbone of malaria prevention worldwide — cheap, well-tolerated, and simple to dose weekly. That changed as Plasmodium falciparum acquired mutations in the pfcrt transporter gene, spreading resistance from Southeast Asia in the late 1950s across virtually every falciparum-endemic region on Earth. Today, chloroquine-sensitive falciparum survives in only a few pockets, and travel medicine now begins with one question: is chloroquine even on the table for this destination?
Chloroquine works by concentrating in the parasite digestive vacuole and blocking detoxification of heme released during hemoglobin digestion — a mechanism the parasite cannot easily route around without a transporter change. The pfcrt mutation does exactly that: it lets the parasite pump chloroquine back out of the vacuole before it can act.
Once this mutation appeared, it spread along trade and travel routes, and clinical failure rates climbed wherever it took hold. For travel medicine, this reframed the entire prophylaxis conversation: instead of asking "which dose of chloroquine," clinicians began asking "is this destination even chloroquine-sensitive," because prescribing chloroquine to a traveler heading into a resistant zone offers little real protection.
Regional resistance mapping — built from surveillance data, in vitro susceptibility testing, and reported treatment failures — is now the first input into any chemoprophylaxis decision, functioning as a geographic gatekeeper before dosing schedules or side-effect profiles are even discussed.
A small number of destinations are still considered chloroquine-sensitive, meaning chloroquine (or in some guidance, hydroxychloroquine) remains an appropriate, simple, once-weekly option: parts of Central America north and west of the Panama Canal, the island of Hispaniola (Haiti and the Dominican Republic), and a handful of areas in the Middle East and North Africa with low-intensity, largely non-falciparum transmission.
Outside these pockets, chloroquine-resistant P. falciparum predominates, and travelers require one of the newer regimens — atovaquone-proguanil, doxycycline, or mefloquine — chosen according to trip length, tolerability, and contraindications rather than convenience alone.
The practical rule of thumb: always confirm resistance status for the specific destination and itinerary before defaulting to chloroquine — a traveler transiting through both a sensitive and a resistant area needs the regimen appropriate for the higher-risk zone.
Once chloroquine is ruled out, three regimens dominate modern travel-medicine practice: atovaquone-proguanil, doxycycline, and mefloquine. None is universally "best" — each trades off dosing burden, side-effect profile, cost, and contraindications differently, and the right choice depends on the traveler in front of you as much as the destination on the map.
Atovaquone-proguanil combines a mitochondrial electron-transport inhibitor with a synergistic antifolate, giving activity against both liver-stage and blood-stage parasites. Its defining practical advantage is the short pre- and post-travel window: start just 1–2 days before entering a malarious area and stop only 7 days after leaving, versus the four-week tail required by doxycycline or mefloquine.
It is generally well tolerated, with gastrointestinal upset being the most common complaint, and it is often favored for shorter trips where a compressed course reduces the total pill burden and the chance of missed doses. Cost is typically higher per day than doxycycline, which can matter for extended stays.
Doxycycline is a tetracycline-class antibiotic with reliable activity against blood-stage parasites and the practical bonus of preventing several other travel-related infections (e.g., leptospirosis, some rickettsial diseases). It is inexpensive and widely stocked, making it attractive for long-duration travel or resource-limited settings.
The trade-off is a longer dosing tail — daily dosing must continue for 4 weeks after leaving the malarious area, on top of daily dosing during the trip — and it requires sun-sensitivity precautions (photosensitivity reactions) plus avoidance in pregnancy and in young children due to effects on developing teeth and bone.
Mefloquine is dosed just once weekly, which can be the deciding factor for travelers on long assignments or those who struggle with daily pill regimens. It also starts earlier than the other options — 2–3 weeks before departure — partly to allow any early tolerability issues to surface before travel.
Its main limitation is a well-known neuropsychiatric side-effect profile in a subset of users (vivid dreams, anxiety, and in rarer cases more significant psychiatric symptoms), which makes it unsuitable for travelers with a psychiatric history or seizure disorder. For the right traveler, though, its low total dose count on multi-month trips is a meaningful adherence advantage.
Total dose count often favors mefloquine on long trips (fewer weekly doses) while atovaquone-proguanil favors short trips (shortest total course length) — duration alone can tip the comparison before contraindications are even considered.
Efficacy on paper means little if a traveler cannot realistically stick to the schedule. Each regimen defines a start window, an in-country cadence, and a post-travel tail, and the length of that full course — not just the drug's pharmacology — often predicts whether prophylaxis is actually completed.
Atovaquone-proguanil: start 1–2 days before entering the malarious area, take one dose daily throughout the trip, continue for 7 days after leaving. This is the shortest total course among the three regimens, which is a major adherence advantage for short trips.
Doxycycline: start 1–2 days before, one dose daily throughout, continue daily for 4 weeks after leaving. The daily cadence is easy to remember but the long post-trip tail is where adherence often breaks down — travelers stop taking it once they feel "safely home."
Mefloquine: start 2–3 weeks before departure (to pre-screen tolerability and reach steady state), one dose weekly throughout the trip, continue weekly for 4 weeks after leaving. Weekly dosing means far fewer total doses on long trips, but the pre-travel lead time requires earlier planning.
Studies of prophylaxis adherence consistently find that longer post-travel tails correlate with higher rates of early discontinuation — travelers are motivated while anticipating risk, but that motivation fades once they are home and feeling well, precisely when doxycycline and mefloquine still require weeks of dosing.
This is a central reason atovaquone-proguanil is often preferred for shorter trips: its 7-day tail is easy to complete. For longer trips, mefloquine's weekly cadence can mean fewer total "opportunities to forget" than 30+ consecutive daily doses, even though its lead-in requires more advance planning.
A simple planning heuristic: total dose count for atovaquone-proguanil grows one-for-one with trip length plus 8 fixed doses, while mefloquine grows roughly one dose per 7 days of trip length plus 6 fixed doses — meaning mefloquine's relative dosing burden drops as trips get longer.
No chemoprophylaxis regimen is universally safe. Before any recommendation is finalized, a structured screen for contraindications rules out options that could harm a specific traveler — regardless of how well that drug otherwise fits the destination and trip length.
Mefloquine's neuropsychiatric side-effect profile means it should be avoided in travelers with a history of psychiatric illness (depression, anxiety disorders, psychosis) or seizure disorder, since it can precipitate or worsen symptoms in susceptible individuals. Because the drug is started 2–3 weeks before travel, any early warning signs of intolerance during that lead-in period should prompt a switch to an alternative regimen well before departure.
Doxycycline is contraindicated in pregnancy and in young children because tetracyclines bind to developing bone and teeth, causing staining and potential growth effects. It also requires counseling on photosensitivity — sunburn-like reactions can occur with sun exposure — so sunscreen and protective clothing become part of the prescription, not an afterthought.
Atovaquone-proguanil is generally well tolerated but should be avoided in travelers with severe renal impairment, since proguanil and its active metabolite are renally cleared and can accumulate to problematic levels when kidney function is significantly reduced. Milder renal impairment may still warrant dose review rather than an outright switch, but severe impairment moves this option off the table.
Contraindication screening is not a single yes/no gate — it is a checklist run against every candidate regimen simultaneously, because ruling out one option (say, mefloquine for a seizure history) still leaves two others to evaluate against the remaining criteria.
The final chemoprophylaxis recommendation is never a single lookup — it is the intersection of four inputs: the destination's resistance pattern, the trip's duration, the traveler's contraindications, and, where multiple safe options remain, the traveler's own preference for pill burden versus dosing frequency.
Step 1 — Geography: does the itinerary fall in a chloroquine-sensitive pocket, or a chloroquine-resistant zone (the majority of endemic destinations)? This determines whether chloroquine is even a candidate.
Step 2 — Duration: a short trip favors the compressed atovaquone-proguanil course; a long-duration stay shifts the total-dose-count advantage toward mefloquine's weekly schedule, while doxycycline remains a cost-effective daily fallback for extended trips when mefloquine is unsuitable.
Step 3 — Contraindications: screen every remaining candidate against the traveler's history — psychiatric/seizure history removes mefloquine, pregnancy or young age removes doxycycline, severe renal impairment removes atovaquone-proguanil.
Step 4 — Preference: when more than one option survives screening, let the traveler weigh in — some strongly prefer fewer total doses (mefloquine), others prefer the shortest possible course (atovaquone-proguanil) or the lowest cost (doxycycline).
Because the inputs are itinerary-specific, the same traveler can receive a different recommendation for a different trip — a two-week conference in a chloroquine-sensitive country calls for a different conversation than a six-month posting in a highly endemic, chloroquine-resistant region. Any change to destination, duration, or newly disclosed medical history should trigger a re-run of the same funnel rather than reuse of a prior prescription.
The output of this simulator's final stage is illustrative only — always confirm chemoprophylaxis choice against current destination-specific guidance (e.g., CDC Yellow Book or WHO recommendations) and an individualized clinical assessment.