Atovaquone-proguanil versus mefloquine for malaria prophylaxis in nonimmune travelers: results from a randomized, double-blind study

Safety evaluation of the drugs available to prevent malaria

All drugs used for malaria prophylaxis have common adverse effects, in addition to rare and/or severe adverse effects. For many of the drugs in current use, the common adverse effects include neuropsychiatric harms. This property makes these drugs unpopular with tourists and business travellers, most of whom will be well at the start of chemoprophylaxis. Drugs available to prevent malaria have not been rigorously researched in terms of the phenomenology of their unwanted effects. Consequently, prescribers are not well placed to give useful information to travellers on the incidence, natural history and avoidability of the harms they may experience from malaria chemoprophylaxis. There is some evidence that the adverse effects of mefloquine may be a post-hepatic syndrome caused by drug-induced liver damage with, in some users, symptomatic thyroid disturbance. However, confusion in the interpretation of the scientific evidence has led to conflicting messages regarding the safety of mefloquine and other antimalaria drugs, and to incorrect self-therapy by individual travellers, sometimes with fatal outcomes. In this review, the existing knowledge base for the safety of drugs currently used to prevent malaria is described along with present designs for future studies that would allow a rigorous safety assessment of candidate chemoprophylactic agents and of new drugs introduced to prevent malaria. There is an urgent need for internationally-agreed, evidence-based malaria prevention guidelines. These guidelines should be explicitly linked to the best available research evidence (normally systematic reviews of trials and individual randomised trials) and should highlight gaps in the knowledge base as priority areas for research.

Adverse effects of the antimalaria drug, mefloquine: due to primary liver damage with secondary thyroid involvement?

BACKGROUND

Mefloquine is a clinically important antimalaria drug, which is often not well tolerated. We critically reviewed 516 published case reports of mefloquine adverse effects, to clarify the phenomenology of the harms associated with mefloquine, and to make recommendations for safer prescribing.

PRESENTATION

We postulate that many of the adverse effects of mefloquine are a post-hepatic syndrome caused by primary liver damage. In some users we believe that symptomatic thyroid disturbance occurs, either independently or as a secondary consequence of the hepatocellular injury. The mefloquine syndrome presents in a variety of ways including headache, gastrointestinal disturbances, nervousness, fatigue, disorders of sleep, mood, memory and concentration, and occasionally frank psychosis. Previous liver or thyroid disease, and concurrent insults to the liver (such as from alcohol, dehydration, an oral contraceptive pill, recreational drugs, and other liver-damaging drugs) may be related to the development of severe or prolonged adverse reactions to mefloquine.

IMPLICATIONS

We believe that people with active liver or thyroid disease should not take mefloquine, whereas those with fully resolved neuropsychiatric illness may do so safely. Mefloquine users should avoid alcohol, recreational drugs, hormonal contraception and co-medications known to cause liver damage or thyroid damage. With these caveats, we believe that mefloquine may be safely prescribed in pregnancy, and also to occupational groups who carry out safety-critical tasks.

TESTING

Mefloquine's adverse effects need to be investigated through a multicentre cohort study, with small controlled studies testing specific elements of the hypothesis.

Malarone treatment failure and in vitro confirmation of resistance of Plasmodium falciparum isolate from Lagos, Nigeria

We report the first in vitro and genetic confirmation of Malarone (GlaxoSmithKline; atovaquone and proguanil hydrochloride) resistance in Plasmodium falciparum acquired in Africa. On presenting with malaria two weeks after returning from a 4-week visit to Lagos, Nigeria without prophylaxis, a male patient was given a standard 3-day treatment course of Malarone. Twenty-eight days later the parasitaemia recrudesced. Parasites were cultured from the blood and the isolate (NGATV01) was shown to be resistant to atovaquone and the antifolate pyrimethamine. The cytochrome b gene of isolate NGATV01 showed a single mutation, Tyr268Asn which has not been seen previously.

Recent Advances and New Challenges in Travel Medicine

Recent advances in travel medicine include the use of computer resources to obtain information on outbreaks and recommendations to travelers, the introduction of atovaquone/proguanil as chemoprophylaxis and treatment for malaria, the use of azithromycin as an alternative in the self-treatment of traveler's diarrhea, and the combination of hepatitis A and hepatitis B vaccines. At the same time, new challenges continue to appear. Shifts in the distribution of infections, such as West Nile virus and dengue fever, underscore the need for up-to-date information. Well-known infectious diseases, such as polio, meningococcal meningitis, and influenza are appearing in unexpected ways and settings. It is increasingly clear that travelers, while at risk for infections, also play a role in the global dispersal of pathogens, such as certain serogroups of Neisseria meningitidis and influenza. Increasing drug resistance affects the choice of drugs for treatment and chemoprophylaxis, and decisions about use of vaccines. Newly identified adverse events associated with yellow fever vaccine have prompted enhanced surveillance after vaccination and careful scrutiny of appropriate indications for the vaccine.

Malaria chemoprophylaxis in the age of drug resistance. I. Currently recommended drug regimens

As international travel becomes increasingly common and resistance to antimalarial drugs escalates, a growing number of travelers are at risk for contracting malaria. Parasite resistance to chloroquine and proguanil and real or perceived intolerance among patients to standard prophylactic agents such as mefloquine have highlighted the need for new antimalarial drugs. Promising new regimens include atovaquone and proguanil, in combination; primaquine; and a related 8-aminoquinoline, tafenoquine. These agents are active against the liver stage of the malaria parasite and therefore can be discontinued shortly after the traveler leaves an area where malaria is endemic, which encourages adherence to the treatment regimen. Part 1 of this series reviews currently recommended chemoprophylactic drug regimens, and part 2 will focus on 8-aminoquinoline drugs.