Randomised trial of mefloquine-tetracycline and quinine-tetracycline for acute uncomplicated falciparum malaria

Polymeric Nanocarriers for the Delivery of Antimalarials

Malaria is an infectious disease caused by a protozoan parasite which is transmitted by female Anopheles mosquitoes around tropical and sub-tropical regions. Half of the world's population is at risk of being infected by malaria. This mainly includes children, pregnant women and people living with chronic diseases. The main factor that has contributed to the spread of this disease is the increase in the number of drug-resistant parasites. To overcome drug resistance, researchers have developed drug delivery systems from biodegradable polymers for the loading of antimalarials. The drug delivery systems were characterized by distinct features such as good biocompatibility, high percentage drug encapsulation, reduced drug toxicity and targeted drug delivery. In this review article, we highlight the various types of drug delivery systems developed from polymeric nanocarriers used for the delivery of antimalarials.

Tetracyclines in malaria

Malaria, a parasite vector-borne disease, is one of the greatest health threats in tropical regions, despite the availability of malaria chemoprophylaxis. The emergence and rapid extension of Plasmodium falciparum resistance to various anti-malarial drugs has gradually limited the number of potential malaria therapeutics available to clinicians. In this context, doxycycline, a synthetically derived tetracycline, constitutes an interesting alternative for malaria treatment and prophylaxis. Doxycycline is a slow-acting blood schizontocidal agent that is highly effective at preventing malaria. In areas with chloroquine and multidrug-resistant P. falciparum parasites, doxycycline has already been successfully used in combination with quinine to treat malaria, and it has been proven to be effective and well-tolerated. Although not recommended for pregnant women and children younger than 8 years of age, severe adverse effects are rarely reported. In addition, resistance to doxycycline is rarely described. Prophylactic and clinical failures of doxycycline have been associated with both inadequate doses and poor patient compliance. The effects of tetracyclines on parasites are not completely understood. A better comprehension of the mechanisms underlying drug resistance would facilitate the identification of molecular markers of resistance to predict and survey the emergence of resistance.

Doxycycline for malaria chemoprophylaxis and treatment: report from the CDC expert meeting on malaria chemoprophylaxis

Doxycycline, a synthetically derived tetracycline, is a partially efficacious causal prophylactic (liver stage of Plasmodium) drug and a slow acting blood schizontocidal agent highly effective for the prevention of malaria. When used in conjunction with a fast acting schizontocidal agent, it is also highly effective for malaria treatment. Doxycycline is especially useful as a prophylaxis in areas with chloroquine and multidrug-resistant Plasmodium falciparum malaria. Although not recommended for pregnant women and children < 8 years of age, severe adverse events are rarely reported for doxycycline. This report examines the evidence behind current recommendations for the use of doxycycline for malaria and summarizes the available literature on its safety and tolerability.

Quinine, an old anti-malarial drug in a modern world: role in the treatment of malaria

Quinine remains an important anti-malarial drug almost 400 years after its effectiveness was first documented. However, its continued use is challenged by its poor tolerability, poor compliance with complex dosing regimens, and the availability of more efficacious anti-malarial drugs. This article reviews the historical role of quinine, considers its current usage and provides insight into its appropriate future use in the treatment of malaria. In light of recent research findings intravenous artesunate should be the first-line drug for severe malaria, with quinine as an alternative. The role of rectal quinine as pre-referral treatment for severe malaria has not been fully explored, but it remains a promising intervention. In pregnancy, quinine continues to play a critical role in the management of malaria, especially in the first trimester, and it will remain a mainstay of treatment until safer alternatives become available. For uncomplicated malaria, artemisinin-based combination therapy (ACT) offers a better option than quinine though the difficulty of maintaining a steady supply of ACT in resource-limited settings renders the rapid withdrawal of quinine for uncomplicated malaria cases risky. The best approach would be to identify solutions to ACT stock-outs, maintain quinine in case of ACT stock-outs, and evaluate strategies for improving quinine treatment outcomes by combining it with antibiotics. In HIV and TB infected populations, concerns about potential interactions between quinine and antiretroviral and anti-tuberculosis drugs exist, and these will need further research and pharmacovigilance.

Activity of azithromycin or erythromycin in combination with antimalarial drugs against multidrug-resistant Plasmodium falciparum in vitro

Azithromycin, an azalide analog of erythromycin was assayed for its in vitro activity against multidrug-resistant Plasmodium falciparum K1 strain by measuring the 3H-hypoxanthine incorporation. Azithromycin caused inhibitory effects on the parasite growth with IC50 and IC90 values of 8.4+/-1.2 microM and 26.0+/-0.9 microM, respectively. Erythromycin inhibited growth of P. falciparum with IC50 and IC90 values of 58.2+/-7.7 microM and 104.0+/-10.8 microM, respectively. The activity of antimalarial drugs in combination with azithromycin or erythromycin against P. falciparum K1 were compared. Combinations of chloroquine with azithromycin or erythromycin showed synergistic effects against parasite growth in vitro. Combinations of quinine-azithromycin and quinine-erythromycin showed potentiation. Additive effects were observed in mefloquine-azithromycin and mefloquine-erythromycin combinations. Similar results were also produced by pyronaridine in combination with azithromycin or erythromycin. However, artesunate-azithromycin and artesunate-erythromycin combinations had antagonistic effects. The in vitro data suggest that azithromycin and erythromycin will have clinical utility in combination with chloroquine and quinine. The worldwide spread of chloroquine-resistant P. falciparum might inhibit the ability to treat malaria patients with chloroquine-azithromycin and chloroquine-erythromycin in areas of drug-resistant. The best drug combinations against multidrug-resistant P. falciparum are quinine-azithromycin and quinine-erythromycin.

Antimalarial drugs - host targets (re)visited

Every year, forty percent of the world population is at risk of contracting malaria. Hopes for the erradication of this disease during the 20th century were dashed by the ability of Plasmodium falciparum, its most deadly causative agent, to develop resistance to available drugs. Efforts to produce an effective vaccine have so far been unsuccessful, enhancing the need to develop novel antimalarial drugs. In this review, we summarize our knowledge concerning existing antimalarials, mechanisms of drug-resistance development, the use of drug combination strategies and the quest for novel anti-plasmodial compounds. We emphasize the potential role of host genes and molecules as novel targets for newly developed drugs. Recent results from our laboratory have shown Hepatocyte Growth Factor/MET signaling to be essential for the establishment of infection in hepatocytes. We discuss the potential use of this pathway in the prophylaxis of malaria infection.

Resposta clínico-parasitológica ao tratamento com quinino associado à doxiciclina em casos de malária falciparum não-complicada

A resposta de portadores de malária falciparum, não-complicada, ao tratamento com quinino mais doxiciclina foi pesquisada em ensaio clínico aberto. A maioria dos portadores (76,2%; n=16) apresentaram plasmódios sensíveis e 23,8% (n=5) resistentes. Este esquema terapêutico parece ser ainda boa opção nos casos de malária falciparum não-complicada.

The future outlook of antimalarial drugs and recent work on the treatment of malaria

With the emergence of multidrug-resistant falciparum malaria, new drugs and drugs in combination are urgently needed. New antimalarial drugs investigated at the Hospital for Tropical Diseases of the Faculty of Tropical Medicine at Mahidol University in Bangkok, Thailand in recent years for treatment of uncomplicated and severe falciparum malaria are as follows: atovaquone, and artemisinin derivatives (artesunate, artemether, arteether, and dihydroartemisinin) combined with other antimalarials.Malarone, artemisinin derivatives combined with lumefantrine or doxycycline, and mefloquine combined with tetracycline or doxycycline have been evaluated with improvement of the cure rate in uncomplicated malaria. Artemisinin derivatives intravenously or intrarectally combined with mefloquine may be alternatives to intravenous quinine for treatment of severe malaria. In Thailand, drug treatment for uncomplicated malaria consists of the combinations or artesunate plus mefloquine or artemether plus lumefantrine or quinine plus tetracycline. In treatment of severe malaria, antimalarial drugs of choice are intravenous quinine or artemisinin derivatives.

Management of malaria in Thailand

The purpose of treatment for uncomplicated malaria is to produce a radical cure using the combination of: artesunate (4 mg/kg/day) plus mefloquine (8 mg/kg day) for 3 days: a fixed dose of artemether and lumefantrine (20/120 mg tablet) named Coartem (4 tablets twice a day for three days for adults weighing more than 35 kg): quinine 10 mg/kg 8-hourly plus tetracycline 250 mg 6-hourly for 7 days (or doxycycline 200 mg as an alternative to tetracycline once a day for 7 days) in patients aged 8 years and over: Malarone (in adult 4 tablets daily for 3 days). In treating severe malaria, early diagnosis and treatment with a potent antimalarial drug is recommended to save the patient's life. The antimalarial drugs of choice are: intravenous quinine or a parenteral form of an artemisinin derivative (artesunate i.v./i.m. for 2.4 mg/kg followed by 1.2 mg/kg injection at 12 and 24 hr and then daily for 5 dayss; artemether i.m. 3.2 mg/kg injection followed by 1.6 mg/kg at 12 and 24 hrs and then daily for 5 days; artemether i.m. (Artemotil) with the same dose of artemether or artesunate suppository (5 mg/kg) given rectally 12 hourly for 3 days. Oral artemisinin derivatives (artesunate, artemether, and dihydroartemisinin with 4 mg/kg/day) could replace parenteral forms when patients can tolerate oral medication. Oral mefloquine (25 mg/kg divided into two doses 8 hrs apart) should be given at the end of the artemisinin treatment course to reduce recrudescence.

Role of cytochrome P450 3A in the metabolism of mefloquine in human and animal hepatocytes

We studied mefloquine metabolism in cells and microsomes isolated from human and animal (monkey, dog, rat) livers. In both hepatocytes and microsomes, mefloquine underwent conversion to two major metabolites, carboxymefloquine and hydroxymefloquine. In human cells and microsomes these metabolites only were formed, as already demonstrated in vivo, while in other species several unidentified metabolites were also detected. After a 48 hr incubation with human and rat hepatocytes, metabolites accounted for 55-65% of the initial drug concentration, whereas in monkey and dog hepatocytes, mefloquine was entirely metabolized after 15 and 39 hrs, respectively. The consumption of mefloquine was less extensive in microsomes, and unchanged drug represented 60% (monkey) to 85-100% (human, dog, rat) of the total radioactivity after 5 hr incubations. The involvement of the cytochrome P450 3A subfamily in mefloquine biotransformation was suggested by several lines of evidence. Firstly, mefloquine metabolism was strongly increased in hepatic microsomes from dexamethasone-pretreated rats, and also in human and rat hepatocytes after prior treatment with a cytochrome P450 3A inducer. Secondly, mefloquine biotransformation in rifampycin-induced human hepatocytes was inhibited in a concentration-dependent manner by the cytochrome P450 3A inhibitor ketoconazole and thirdly, a strong correlation was found between erythromycin-N-demethylase activity (mediated by cytochrome P450 3A) and mefloquine metabolism in human microsomes (r=0.81, P < 0.05, N=13). Collectively, these findings concerning the role of cytochrome P450 3A in mefloquine metabolism may have important in vivo consequences especially with regard to the choice of agents used in multidrug antimalarial regimens.

Genetic analysis of Plasmodium falciparum infections on the north-western border of Thailand

Genetic characterization of Plasmodium falciparum infections in north-western Thailand, a region of low transmission intensity (1 infection/person each year), has found a comparable number of parasite genotypes per infected person to regions with hyperendemic malaria. Clone multiplicity and parasite diversity were found to be homogeneous across 129 infected individuals comprising a range of age-groups (1.32 parasite genotypes; n = 98), patients (aged 2-16 years) with recrudescent infections (1.54; n = 13), and pregnant women (1.61; n = 18). Individuals belonging to groups with a high risk of infection, as deduced by clinical epidemiology, did not harbour a higher number of clones per infection, nor greater parasite diversity than low-risk groups. In fact, multiple genotype infections were as common in low-risk groups, suggesting that there is frequent transmission of polyclonal infections from a single inoculum, rather than superinfection. Such a polyclonal transmission system would enable generation of extensive parasite diversity by recombination, despite the low level of transmission. However, co-infection with P. vivax was associated with fewer P. falciparum genotypes per infection.

A physicochemical study of the tetracycline coordination to oxovanadium(IV)

The interaction of tetracycline and oxovanadium(IV) in aqueous solution was studied by potentiometric and spectrophotometric methods. Oxovanadium(IV) ions form both a positively charged 1:1 and a neutral 2:1 metal-ligand complex with tetracycline. When a 1:1 ligand-to-metal ratio mixture is used at about pH 4.5 the 1:1 species predominates, being replaced at pH 6 by the binuclear complex. The binuclear complex has been isolated and fully characterised. Infrared and EPR studies suggest the existence of two distinct vanadyl binding sites. Our results indicate that the first vanadium coordinates to the BCD-ring system and the second one to the A-ring. Biological implications of the existence of a neutral complex at physiological pH are briefly discussed.

Blood-stage dynamics and clinical implications of mixed Plasmodium vivax-Plasmodium falciparum infections

We present a mathematical model of the blood-stage dynamics of mixed Plasmodium vivax-Plasmodium falciparum malaria infections in humans. The model reproduces features of such infections found in nature and suggests several phenomena that may merit clinical attention, including the potential recrudescence of a long-standing, low-level P. falciparum infection following a P. vivax infection or relapse and the capacity of an existing P. vivax infection to reduce the peak parasitemia of a P. falciparum superinfection. We simulate the administration of antimalarial drugs, and illustrate some potential complications in treating mixed-species malaria infections. Notably, our model indicates that when a mixed-species infection is misdiagnosed as a single-species P. vivax infection, treatment for P. vivax can lead to a surge in P. falciparum parasitemia.

A comparison of three different dihydroartemisinin formulations for the treatment of acute uncomplicated falciparum malaria in Thailand

We compared the safety and efficacy of three formulations of dihydroartemisinin for the treatment of acute uncomplicated falciparum malaria in patients who received a total dose of 600 mg dihydroartemisinin over 5 days. The first group was treated by dihydroartemisinin produced and formulated in the People's Republic of China, the second group was treated by dihydroartemisinin produced in Vietnam but formulated by the Government Pharmaceutical Organization of Thailand and the third group was treated by dihydroartemisinin produced and formulated by the Government Pharmaceutical Organization of Thailand. All patients were admitted to hospital to evaluate safety and efficacy for a total of 28 days. By the third day of treatment, most patients were blood-smear negative for parasites and none had serious adverse effects. Minor symptoms such as nausea, dizziness and headache were similar in the three groups and disappeared after 3 days of treatment. One-hundred and thirty-three patients completed the 28-day follow-up period. The cure rates of groups I, II and III were 80%, 85% and 92%, respectively (P > 0.02). There were no significant differences in fever clearance or parasite clearance among the three groups. We conclude that the three formulations of dihydroartemisinin produced and formulated in different countries were safe and effective in treating uncomplicated falciparum malaria acquired in Thailand.

Monotherapy with sodium artesunate for uncomplicated falciparum malaria in Thailand: a comparison of 5- and 7-day regimens

We compared the safety and efficacy of two treatment regimens using sodium artesunate in 91 randomized patients with uncomplicated falciparum malaria acquired in Thailand. One group of 45 patients received 400 mg of artesunate on the first day of treatment and then 200 mg daily for 4 days for a total of 1200 mg (group I: 5-day treatment). A second group of 46 patients received 400 mg of artesunate on the first day of treatment and then 200 mg daily for 6 days for a total of 1600 mg (group II: 7-day treatment). Both regimens were well tolerated. All patients were followed for a total of 28 days. By the third day of treatment, most patients were blood smear negative for parasites. Eighty-two patients completed the 28-day follow-up period and were used for describing the cure rate. All patients treated with the 5-day regimen were cured. In the 7-day treatment group, 98% (39 of 40) of the patients were cured; one patient developed late recrudescence (RI). There were no significant differences in fever clearance or parasite clearance between the two groups. However, 13 patients (five in group I and eight in group II) developed Plasmodium vivax infection during the follow-up period. We conclude that 5- or 7-day regimens of sodium artesunate with a total dose of 1200-1600 mg are effective and safe in treating falciparum malaria acquired in Thailand.

Therapeutic effects of chloroquine in combination with quinine in uncomplicated falciparum malaria

The efficacy and toxicity of oral quinine combined with oral chloroquine were studied in 50 Thai men with uncomplicated falciparum malaria. All were treated for 7 days with quinine sulphate (10 mg salt/kg every 8 h). Twenty-five of the patients, selected at random, were also given oral tetracycline (4 mg/kg four times daily) over the same period and the remainder were given chloroquine (25 mg base/kg over the first 3 days). There were no serious adverse effects. Overall fever-clearance times (FCT) and parasite-clearance times (PCT) in the chloroquine and tetracycline groups were not significantly different, with mean (S.D.) values of 51 (33) and 41 (27) h for FCT and 80 (25) and 83 (21) h for PCT, respectively. Most of the patients (18 in each group) were followed for > or = 2 months. Recrudescence rates (R1) were significantly higher in the chloroquine group than in the tetracycline group (39% v. 6%; P = 0.02), all recrudescences occurring within 4 weeks (18-25 days) of starting treatment. Subsequent parasitaemia with Plasmodium vivax, however, occurred less frequently in the chloroquine group (11%) than in the tetracycline group (33%) (P = 0.11) and took longer to develop in the chloroquine group [51 or 59 days compared with a mean (S.D.) value of 29 (10) days in the tetracycline group; P = 0.01]. Within the chloroquine group, FCT and PCT were both shorter in those with cure than in those with R1 resistance, with mean (S.D.) values of 41 (25) and 70 (33) h for FCT (P = 0.09) and 72 (20) and 100 (18) h for PCT (P = 0.01), respectively. Chloroquine does not potentiate the clinical response to quinine against resistant strains of uncomplicated falciparum malaria, nor does it convey any useful antipyretic effect.

Treatment of acute, uncomplicated, falciparum malaria with oral dihydroartemisinin

A clinical trial of oral dihydroartemisinin for the treatment of acute, uncomplicated, falciparum malaria involved 53 adult patients in Thailand. Each received a total dose of 480 mg over 7 days (120 mg given immediately, followed by 60 mg/day) after being admitted to the Hospital for Tropical Diseases in Bangkok for 28 days. Most (92%) completed the 28-day follow-up but four patients left the hospital early, for reasons unrelated to their treatment. Most patients showed clinical improvement 1-3 days after starting treatment and none suffered from serious adverse reactions. The cure rate was 90% (44/49). The mean (S.D.) parasite-clearance time was 40.4 (14.1) h and the mean fever-clearance time was 37.0 (30.2) h. Seven patients had a brief increase in parasitaemia after initiation of treatment but subsequent counts declined dramatically. Five patients who failed treatment (RI response) were successfully treated with quinine plus tetracycline for 7 days. No RII or RIII responses were observed. These findings indicate that treatment with oral dihydroartemisinin is effective and well tolerated, and that dihydroartemisinin may be suitable as an alternative treatment for acute, uncomplicated, falciparum malaria. Comparisons with other conventional antimalarial drugs in a large, double-blind, randomized trial and studies of dihydroartemisinin in combination with other, long-acting antimalarials are needed.

Cutaneous delayed-type hypersensitivity responsiveness in patients during and after Plasmodium falciparum and Plasmodium vivax infections

To assess cellular immune function in malaria, 61 patients admitted to the Bangkok Hospital for Tropical Diseases with Plasmodium falciparum (PF) or Plasmodium vivax malaria were examined with the MULTITEST CMI system (Merieux Institute, Florida) to evaluate delayed-type hypersensitivity (DTH) during and after acute disease over 4 weeks. All patients demonstrated significantly decreased responsiveness to seven commonly encountered recall antigens. This deficit was most severe immediately upon admission (prior to therapy). Uncomplicated Pf cases demonstrated significant hyporesponsiveness only during Week 1. Responses in moderate/severe falciparum and all vivax patients gradually increased in Weeks 2 and 3 but remained significantly below control values. This study confirms functional cell-mediated immune deficits in falciparum malaria and, for the first time, shows hyporesponsiveness in vivax malaria. We conclude that malaria causes a pronounced CMI deficit that is still detectable in some individuals for 3-4 weeks after treatment of acute infection. These changes in DTH should be a consideration in future vaccine development and in evaluation of immune status in endemic areas.