The comparative efficacy of chloroquine and sulfadoxine-pyrimethamine for the treatment of uncomplicated falciparum malaria in Kampala, Uganda

The comparative efficacy of chloroquine treatment of uncomplicated falciparum

and sulfadoxine-pyrimethamine malaria in Kampala, Uganda

for the

Moses R. Kamya’*, Grant DorseyZ, Anne Gasasira I, Grace Ndeezil, Juliet N. Babirye’, Sarah G. Staedke’ and Philip J. Rosenthal’ ‘Makerere University Medical School, Kampala, Uganda; ‘Department of Medicine, San Francisco General Hospital and The University of California, San Franc&o, USA Abstract Chloroquine (CQ) remains the first-line treatment for uncomplicated malaria in much ofAfrica despite the growing problem of resistance to this drug. Sulfadoxine-pyrimethamine (SP) is often used after CQ treatment failure and has replaced CQ as the first-line treatment in parts ofAfrica. To compare the efficacy of these 2 regimens, we evaluated, in March-August 1999, clinical and parasitological responses over 28 days in 214 children and adults from Kampala, Uganda, with uncomplicated falciparum malaria. Compared to SP, significantly more patients treated with CQ developed early or late clinical failure (54% vs 1 l%, P C 0.001) andparasitoIogica1 failure (72% vs 30%, P < 0.00 1) during 14 days of follow-up. The risk of treatment failure occurring after day 14 was similar between the 2 treatment groups. Among those treated with CQ, children aged < 5 years were at higher risk of clinical failure than older individuals (76% vs 28%, P < O.OOl), anassociationnot seenwithSP (11% vs lo%, P = 0.91). Ahhoughearlyparasite clearance was significantly better in the SP group (P = O.OOl), fever clearance at day 3 was the same (CQ 85%, SP 86%). These and other recent findings suggest that consideration be given to replacing CQ as the first-line therapy for uncomplicated malaria in Uganda, particularly in young children. Keywords: malaria, Plumodium fakipamm, chemotherapy, chloroquine, sulfadoxine-pyrimethamine, drug resistance, Uganda

Introduction Antimalarial drug resistance is a large and growing problem. Several East tican studies have reported incidences of parasitological resistance of Piasmodium fukipamm to chloroquine (CQ) ranging from 50% to over80% (BRANDLING-BENNETT~~ aE.,1988;Sm~0~ et al., 1988; WATKINS et al., 1988; BAYOUMI eial., 1989; FOWLER et al.. 1993: PREMII et al.. 1993: WOLDAY etal., 1995). .The kmergknce df CQ’ resistance has been associated with increased malaria specific mortality, especially in children (TRAPE et aZ., 1998). However, most African countries continue to use CQ as the firstline agent to treat uncomplicated malaria (BIGLAND et aE., 1998). The basis for a programmatic decision to disc&tinue the use of CQ as &e first-line drug for malaria remains unclear (BARAT et al.. 1998). Althourrh CQ treatment failures &e common; CQ is safe Gd inexpensive, and it continues to be at least partially effective in semi-immune African populations (HOFFMAN et al, 1984). It is often argued that to limit cost and toxicity, and to forestall the development of drug tesistance, alternatives to CQ should be withheld until they are absolutely required (WHO, 1994). Recent studies in Uganda have identified high rates of resistance of malaria parasites to CQ. A study from western Uganda reported 58% clinical and 77% patasitological failure among children aged < 5 years (Ugandan Ministry of Health, 1997, unpublished data). A study in Kampala revealed 62% clinical and 86% parasitological failure in children aged < 5 years, although failure rates were significantly lower in older individuals (DORSEY et al., 2000). Sulfadoxine-pyrimethamine (SP) is currently the second-line agent for uncomplicated~malaria in U.&da. Resistance to SP in East Africa has eenerallv been found to be uncommon (NWANYANWU et>l., 199k; FALASCHI & ANSALONI, 1997; VERHOEFF et aZ., 1997) but has begun to emerge in areas with increased drug pressure (WOLDAY et al.. 1995; BONN et al., 1996). In Uganda, limited data primarily- from asymptomatic children revealed uarasitoloeical failure rates iti viwo of O-5% during ;be late lu98Os and 1990s (KAMUGISHA et al., 1994;NEvILL et al., ~~~~;NDYOMUGYENYI & IMAG Address for correspondence: Moses R. Kamya, Department of Medicine, Makerere University, P.O. Box 7072, Kampala, Uganda; hone +256 041 541188; fax $256 041 533531, e-mait [email protected]

clinical trial,

NUSSEN, 1997). A more recent study in western Uganda reported a 12% clinical failure rate of SP for 122 children with symptomatic malaria (JELINEK et al., 1999). In summary, recent data suggest that resistance to CQ in Uganda is unacceptably high. Similar findings in other East African countries have led to recent decisions to change the recommendation for first-line therapy of uncomulicated malaria from CO to SP (BLOLAND et al., l-993). However, such a chaige may increase cost and toxicity, and may contribute to the selection of multidrug-resistant parasites. In addition, CQ therapy may offer clinical benefits beyond its antiparasitic activity, due to a postulated antipyretic effect (BOIANG et al., 1998). In 2 studies from West Africa, children treated with SP were more likelv than those treated with CO to develbp early clinical filure despite improved parasite clearance in those treated with SP, suggesting that an antipyretic effect of CQ was clinically relevant (MILLER et al., 1996; ONYIORAH e6 aZ., 1996). To compare the practical utility of CQ and SP in an urban population in Uganda, we evaluated clinical and parasitological outcomes following treatment with the 2 agents in patients presenting with uncomplicated falciparum malaria in Kampala. Materials and Methods Study site The study was conducted between March and August 1999 at the Old Mulago Hill Dispensary in Kampala, Uganda. Malaria is meso-endemic in Kampala, occurring perennially with peaks during the 2 rainy seasons (Ugandan Ministry of Health, unpublished data). Old Mulago Hill Dispensary is an outpatient clinic that provides primary care for patients from lower socioeconomic areas of Kampala. Services at the dispensary were provided free of charge. Smdypartica’pants andprotocol Consecutive satients with svmntoms of acute uncomplicated malarii and a posi&e*screening thick blood smear (stained with 10% Lcishman’s stain for 10 mini were referred for study enrolment. Patients were enrolled if they met the following inclusion criteria: (i) age 3 6 months, (ii) an elevated temperature at presentation (2 38.O”C tympanic or 375°C axillary) ot a history of fever in the previous 48 h, (iii) P. fczlcipamm monoinfection with 2 2000 asexual parasites/&L measured by thick blood smear, (iv) absence of other causes of fever (based on the clinical judgement of the study physician),

SULFADOXINE-PYRIMETHAMINE

FOR FALCIPARUM

MALARKA

(v) absence of severe malaria (WHO, 1990) or danger signs (inability to stand or drink, recent convulsions, lethargy, or persistent vomiting in children aged < 5 years), (vi) absence of a history of an allergic reaction to sulphonamides, (vii) willingness of the patient or an adult guardian to provide informed consent, and (viii) residence within the city of Kampala. Patients enrolled in the study were evaluated by a study physician for symptoms, duration of the current illness, therapy during the prior 2 weeks, weight, height, spleen size (Hackett’s classification system) and measurement of the core temperature using an electronic rympanic thermometer. Blood was collected by venepuncture on the day of enrolment and by fingerprick on follow-up days. Treatment and follow-up Treatment was assigned en bloc on alternate recruitment days using 25 mg/kg of CQ (Avloclor, ZENECA, 10 mg/kg on days 0 and 1,5 mg/kg on day 2) or a single dose of 1.25 mg/kg pyrimethamine and 25 mg/kg sulfadoxine (Fansidar, Roche) All doses of study drug were administered under direct observation. If a patient vomited within 30 min of dosing, the medication was re-administered. Paracetamol was administered to all patients who were febrile. Patients were followed on days 1,2,3,7, 14, 21 and 28. Follow-up consisted of a brief clinical examination and a questionnaire given by the medical officer on each scheduled follow-up day. Patients were encouraged to come back to the clinic at any time ifthey felt ill, and they then received a full evaluation including examination of a blood smear, Patients who met criteria for clinical failure with CQ were treated with SP and those who failed therapy with SP were treated with oral quinine (10 mg salt/kg every 8 h for 7 days). If patients did not return for scheduled follow-un. thev were visited and assessed at home. If patients co;id no; be located by the home health visitor, they were classified as lost to follow-up. Patients were excluded from the study for the following reasons: (i) administration of any additional antimalarial drugs, (ii) emergence of any nonmalarial febrile illness that would interfere with rhe classification of malaria-treatment outcome, (iii) movement away from the study area, or (iv) withdrawal of informed consent. Laborawry tests Thin blood smears (obtained on day 0) and thick blood smears (obtained on days 0,3,7, 14, 21, and 28) were stained with 2% Giemsa stain for 30 min, and parasite densities were calculated by counting the number of asexual parasites per 200 white blood cells (WBC) assuming a WBC count of 8OOO/pL of blood. On day 0, haematocrit testing was done using the Hawksley microhaematocrit calibration system and urine was tested for the presence of 4-aminoquinolines using the SakerSolomons test (MOUNT et al., 1989). Outcome measurements

Clinical responses to therapy over 14 and 28 days of follow-up were classified according to the revised WHO in-vivo protocol for areas of intense-transmission (WHO, 1996). Patients were classified as ‘earlv treatment failure’ (ETF) if they developed danger signs or severe malaria on ot before day 3, had fever and a day-2 parasite density greater than that on day 0, had fever and parasitaemia on day 3, or had a day-3 parasite density 3 25% of that on day 0. ‘Late treatment failure’ (LTF) was defied as parasitaemia after day 3 with a documented temperature > 38,O”C (tympanic), danger signs, or severe malaria. In addition, patients with an undocumented historv of recent fever and rising parasitaemia were classified as LTF. All others were classified as ‘adeauate clinical response’ (ACR). Parasitological response’@, RI-RIII) was determined using modified WHO criteria (WHO, 1994). If the day-3 parasite density was 2 25% of the

51

IN UGANDA

day-0 density, the response was classified as RIII resistance. If the day-3 density was < 25% of the day-0 density and the patient was patasitaemic on day 4-7, the response was classified as RII. RI parasitological responses were defined as day-3 parasite densities < 25% of day-0 density, a negative blood smear on day 7, and reappearance of patasitaemia during the remainder of the follow-up period. Patients with day-3 parasitaemia < 25% of that on day 0 and negative smears for the remainder of the follow-up period were classified as sensitive (S). To allow categorization with both resistance-classification schemes, minor modifications were made such that patients with ETF and day-2 parasite density > 25% of day 0 were classified as RIII and patients with ETF and day-2 or day-3 parasite density < 25% of day 0 were classified as RII. ‘Fever clearance’ was defined as a tympanic temperature of < 38°C with no report of fever during the previous 24 h. Statistical analysis Data were recorded on standardized case report forms, reviewed dailv for accutacv and comoleteness, and entered into l?piInfo version 6.04 (Centers for Disease Control and Prevention, Atlanta, GA, USA). Clinical success was defined as ACR and clinical failure defined as ETF or LTF. Parasitological sensitivity was defined as an S response and parasitological resistance defined as an RI-RI11 response. Proportions were compared using x2 tests. Analysis of variance (ANOVA) was used for normally distributed continuous data; parasite densities were normalized using logarithmic transformation. The Wilcoxon rank-sum t&t was used for non-normal data. Relative risks. 95% confidence limits. and P-values were calculated to compare outcomes between the treatment groups stratified by age. Relative risks (RI&) were compared by the Breslow-Day test for homogeneity. e

A

Results Of 561 patients referred for screening, 214 were enrolled in the study (CQ 108, SP 106). The primary reasons for exclusion were residence outside the city of Kampala (28%), insufficient parasitaemia (22%), lack of consent (1 1%), concomitant febrile illness (8%), or no measurable fever or history of recent fever (7%). Eightyseven percent ofpatients completed 14 days offollow-up (CQ94, SP 93) and 83% completed 28 days offollow-up (CQ 90, SP 87). There were no significant differences in baseline characteristics between those who completed and those who did not complete the study. Patients treated with CQ (108) and SP (106) were similar in their baseline characteristics including age, sex, prior antimalarial therapy, proportion with fever on day 0, and parasitological and haematological indices (Table 1). The 14-day responses to therapy are summarized in Tables 2 and 3. Considerinn either clinical or parasitological parameters, SP was &nificantly more efficacious than CO. The incidence of clinical failure was 54% with CQ versus 11% with SP (RR 5.1, 95% confidence interval [CI] 2.7-9.3) and the incidence of parasitological failure was 72% with CQ versus 30% with SP (RR 2.4, 95%CI 1.7-3.4). The incidence of clinical and parasitological resistance presenting between days 15 and 28 was similar for the 2 treatment groups. Among patients who were classified as ACR at day 14 and completed 28 days of follow-up, 44% (17 of 39) in the CQ group and 34% (26 of 77) in the SP group subsequently fulfilled criteria for LTF (P = 0.3). Considering parasitological criteria, 55% (12 of 22) in the CQ group and 43% (27 of 63) in the SP group presented with parasitaemia after a negative smear on day 14 (I, = 0.34). Although fever clearance by day 3 was similar in the 2 treatment groups (CQ 85%, SP 86%), early parasite clearance was significantly better in the SP group. By day 3,44 (46%) of 96 in the CQ group compared to 60 (62%) of 97 in the SP group had no detectable parasites

MOSESR.K.AMyA ETAL.

52

Table 1. Baseline characteristics of the 214 falciparum malaria patients enrolled into the study of chloroquine (CQ) or sulfadoxine-pyrimethamine (SW

SP

P

patients

patients

value

Number enrolled 108 Gender (% female) 53 Median age in years 4.0 Age < 5 years (%) 55 Reported antimalarial use in past 2 weeks (%)’ Reported CQ use in past 2 weeks (%)” z; Positive urine CQ test (%)” 76 Palpable spleen (%) 36 Mean duration of fever (days) 3.1 Initial temperature 2 38.0°C (%) 44 Mean haematocrit 24 Haematocrit < 25% (%) Geometric mean parasite density (per pL) 3195869 Parasite density > 100 OOO/J.LL(%) 22

106 51 4.3 51 65

0.14 0.79 0.94 0.59 0.13 0.73 0.75 O-36 0.78 0.77 0.17 0.28 O-38 0.31

CQ

Characteristic

+: 30 3.2 42 25 38 3;: 28

“Includes only patients for whom data were collected. Table 2. Clinical outcomes at day-14 follow-up of treatment malaria with chloroquine (CQ) or sulfadoxine-pyrimethamine pala, Uganda, 1999) CQ (n = 94)

of falcipanun (SP) (Kam-

SP (n = 93)

n

%

95%CI

n

%

95%CI

ACR ETF LTF

43 ;;

44 23 31

35-56 15-33 22-41

83 :

89 5.4 5.4

81-95 2-12 2-12

Sensitive (ACR) Resistant (ETF+LTF)

;:

46 54

35-56 44-65

83 10

89 11

81-95 5-19

Outcome group

ACR, adequate clinical response; ETF, earty treatment failure; LTF, late treatment failure.

Table 3. Parasitological outcomes at day-14 follow-up of treatment falciparum malaria with chloroquine (CQ) or sulfadoxine-pyrimethamine (SP) (Kampala, Uganda, 1999) CQ (n = 94) Outcome group

SP (n = 93)

n

%

95%CI

n

%

95%CI

s RI ~~1

26 19 ;:

28 20 ;;

19-38 13-30 21-40 14-32

65 16 ;

70 17 ;:;

60-79 lo-26 2-12 3-15

Sensitive (S) Resistant (R)

26 68

28 72

19-38 62-81

26:

::

60-79 21-41

(P = 0.03). The geometric mean parasite density on day 3 was lOl/pL in the CQ and 15/pL in the SP group (P = 0*002>. When stratified for age, patients aged < 5 years were signii?cantly more likely than older patients to be both clinical and parasitological failures after CQ treatment (Figure), In contrast, for patients treated with SP, there was no significant association between age and treatment outcome (Figure). In a direct comparison of drug efficacy stratified for age, the risk of clinical failure in patients aged < 5 years was almost 7 times higher (RR 6*9,95%CI 3.0-160) in the CQgroup compared to the SP group, but less than 3 times higher (RR 2+7,95%CI l*O-7.0) in the older age-group (Table 4). Discussion In a comparative efficacy trial of CQ and SP for the treatment of uncomplicated falciparum malaria in Kam-

of

pala, Uganda, we found significantly higher levels of clinical and parasitological resistance to CQ than to SP. Patients treated with CQ were 5 times more likely than those treated with SP to be clinical failures by day 14. Our study site provides primary care to an urban population with high malarial endemicity and CQ use prior to presentation is very common. Although resistance rates may be different in other settings or in populations with a different malarial endemicity (NDYOMUGYENYI& ~L%G NUSSEN, 1997), the high rates of CQ resistance and relatively low rates of SP resistance identified in our study are consistent with recent reports from other areas of Uganda (NDYOMUGYENYI & MAGNUSSEN, 1997; Ugandan Ministry of Health, 1997, unpublished data). These data suggest that the recommendation for CQ as first-line therapy for uncomplicated malaria in Uganda should be reconsidered. Compared to olderpatients, those aged < 5 years were

SULFADOXINE-PYRIMETHAMINE

FOR FALCIPARUM

MALARlA

59

IN UGANDA

Parasitological resistance

Clinical resistance - 96%

lOO%76%

80X-

60%-

60%44%

40% -

40%-

28%

11%

10%

20%-

I (RR z:

330/o

0%

,

CI 1.7-4.5)

I

CQ

(RR 1,1,95% CI 0.3-3.4)

95%

(RR 2.2,95%

(RR

SP 1.2,95x

,

CI 0.6-2.3)

CI 1.3-3.1)

Figure. Day-14 clinical and parasiroiogicaI resistance of falcipacum malaria in z&u to chIoroquine (CQ) and sulfadoxinepyrimerhamine (SP) stratified by age-group (Kampala, Uganda, 1999). White columns, patients aged < 5 years; black columns, patients aged 2 5 years. Table 4. Association between falciparum quine {CQ) or sulfadoxine-pyrimethamine age (Kampala, Uganda, 1999) Treatment

group (n)

Clinical outcome Age < 5 years CQ (51) SIJ (45) Age z 5 years :l$g Parasitological Age < 5 years :l?$5y Age 3 5 years CQ (43) SP (48) . ,

malaria treatment with chloro(SP) and outcome stratified by

Failures

Relative risk

95?/oCI

39 5

6.9” 1.0

3.0- 164 -

12

2.7” 1.0

1.0-7.0

5

49 15

2,9” I.0

1.9-44 -

:s

::g

-

outcome

h

0.9-2.9 -

Risk of treatment failure for CQ vs SP among the 2 age-groups differs significantly (“P T 0.01 and bE’< 0.001). more likely to fail therapy with CQ, an association not found with SP. Thus. the benefit ofSP over CO was more pronounced in your&children. In highly endemic areas, antimalarial immunity increases with age, and it has been postulated that the effectiveness of antimalarial drugs is affected by the immune status of the host (BAIRD et aE., 199 1; TARGE~T, 1992). Previous studies of mefloquine treatment in Thailand (FONTANET & WALKER, 19931, and CQ treatment in the Solomon Islands (HESS et al., 19961. Tanzania (EKVALL er al.. 19981 and at our studv site (~OFSEY et dZ., ZOOO), have also deported younger age as an independent predictor of treatment failure. These results suggest that, in endemic areas, resistance will be detectable first in vounz children and wiIl disproportionately affect younger, Lss-immune patients as the level of resistance increases. It is not clear if the lack of association between age and efficacy in the W-treatment group in our study was due to inadequate statisrical power or fundamental differences in resistance to SP compared to CQ. One hypothesis is that when resistance is uncommon (as with SP in this study), hosr: immunity (and thus age) has a minimal impact on treatment outcome. Following this hypothesis, if resistance to SP in a given population increases, one would expect young children to be disproportionately affected. Alternatively, the association between drug efficacy and age may vary owing to differences in the underlying mechanisms of drug resistance for CQ and SP. SP sensitivity may be bimodal in Kampala, with parasites either highly sensitive or highly resistant to the

drug. In this case, antimalarial immunity may play a relatively minor role in cIinica1 outcome. In contrast, many infections may be caused by parasites with intermediate sensitivity to CQ, allowing a stronger role for immunity in determining clinical outcome after therapy. If this is the case, one can predict that, as CQ resistance worsens over time, the greater prevalence of highly resistant parasites will contribute to increasingly poor outcomes, even in older, more immunologically prepared patients. Our results and others suggest that age-dependent guidelines for antimalarial d@ use may bi appropriate in Darts of Africa. In areas with a hi& mevalence of CO resistance, CQ may stiII be appro$kr ro treat older patients with uncomplicated malaria, while SP or other agents will be necessary for young children. An agedependent treatment policy should decrease the use of alternative antimalarials, and thus slow the emergence of resistance to these agents. The prevalence of CQ resistance at our urban study site was expected to be high, but the role of resistance in determining short (O-3 day), inrermediate (3-14 day) and longer-term (15-28 day) clinical responses to CQ and SP was unclear. It has been argued that, compared to SP, CQ provides greater early symptomatic relief due to an antipyretic effect independent of its parasitolo&cai effect (BOJANG et aZ., 1998). In contrast to other studies (MCJLLER etal., 1996; ONYIORAH etaE., 1994), wefound that the 2 drugs produced equivalent early clinical responses (fever clearance at day 3), although this finding

54

may have been influenced by our liberal use of paracetamol. In contrast to a marked difference during 14 days of foIlow-up, there was no significant difference in the risk for treatment failure between the CO- and SPtreatment groups during longer-term (15-2$ day) follow-up. This result suggests that, in our population, presentations of malarial illness 3 14 days after treatment were mostly due to reinfection (by a strain introduced after the initial treatment), rather than recrudescence (with a strain that was inhibited, but not eradicated by treatment). Studies of the genotypes of parasites infecting patients before and after therapy will be helphI in elucidating better the nature of late drug failures. However, our results and others (WHO, 1996; BLOLAND et al., 1998) suggest that, in areas of intense transmission, a 14-day follow-up period is most appropriate to assess the efficacy of antimalarial drugs. In summary, our data indicate that CQ is no longer efficacious in treating the majority of patients that present with uncomplicated falciparum malaria in Kampala. SP, the second-line therapy in Uganda, was far superior. However, resistance to Sl? also appears to be increasing. The 11% incidence of clinical resistance and 30% incidence of parasitological resistance that we observed offer a strong clue that the efficacy of this drug will also be increasingly limited by drug resistance. As has been clearly communicated by others @LOLAND et al., 1998), it is imperative that we rethink recommendations for antimalarial chemotherapy in Africa. Evaluation of existing drugs [e.g., amodiaquine (OLLIARO et al., 1996)], new agents [e.g., artesunate (VAN AGTMAEL et al., 1999)], and combinations of drugs [e.g., artesunateSP (VON SEIDLEIN et al., 2000), chlorproguanil-dapet al., 1997)], is essential and such sone (iiMuKOYE studies are currently ongoing. More urgently, considerine data &om our 2 studies in KamDala (DORSEY et al.. 2&O) and those from other regi;ns Gf the country (Ugandan Ministry of Health, 1997, unpublished data), it appears that, particularly in young children, CQ is no longer an acceptable first-line therapy for the treatment of uncomplicated malaria in Uganda. Acknowledgements We are indebted to the following members of the study team: clinical officers Moses Ndyamutunga, Seezi R. Musoke; lab technicians Sam Nsoobya, Regina Nakafero and Christopher Bongole; nursing officer Sr B.M. Karakire; home health visitor Sam Nyole; reception Assay Balita; administration Christine Kusasira. We are also indebted to Joel Okullo, Associate Dean, Makerere University Medical School; Charles Karsmagi, Director, Clinical Epidemiology Unit; Fred Wabtie-Mangen, Director, Makerere University Institute of Public Health, Peter Langi, Programme Manager, Malaria Corm01 Unit, Uganda Ministry of Health; Peter Nsubuga, National Tuberculosis and Leprosy Programme in Uganda; and to the subjects who kindly participated in the study. Finally we thank Drs Arthur L. Reingold, Albert Kilian, and Edwin Charlebois for their technical>upport and valuable discussions. This investieation received financial suuuort from the UNDPi World Bank&%-IO Special Programme fh; Research and Training in Tropical Diseases (TDR) and the US National Institutes of Health. References Amukoye, E., Winstanley, P. A., Watkins, W. M., Snow, R. W., Hatcher. T.. Mosobo. M.. Nszumbao, E., Lowe. B., Ton, M., Minyiri,‘&: & Mar&, K: (11997). Chlo&rogu&il-dapsonef effective treatment for uncomplicated falcipamm malaria. Antimicrobial Agents and Chemotherapy, 41,2261-2264. Baird, J. K., Jones, T. R., Danudirgo, E. W., Annis, B. A., Bangs, M. J., Basri, H., Purnomo & Masbar, S. (1991). Agedependent acquired protection against Plasmodiumfakiparum in people having two years exposure to hyperendemic malaria. AmericanJoumalof TmpicalMedicineandHygiene, 45,65-76. Barar, L. M., Himonga, B., Nkunika, S., Bttling, M., Ruebush, T. K., Kapelwa, W. & Bloland, P. B. (1998). A systematic approach io the developmenr of a rational malaria treatment policy in Zambia. Tr0ptia.l Medicine and Inrernational Health, 315355542. Bayoumi,R. A.,Babiker,H. A.,Ibrahim, S. M.,Ghalib, H. W.,

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Received 3 April 2000; revised 13 &ne 2000; accepted fur publication

20June

2000

OF THE ROYAL SOCIETY OF TROPICAL MEDICINE AND I-IYGIENE (2001) 95,55-57

Evaluation of a new sulfadoxine sensitivity assay in vitro for field isolates of Plasmodium falciparum Mathieu Ndounga, Leonardo K. Basco and Pascal Institut de Recherche pour k D.k&ppement Ringwald (IRt)) ~ Laboruroire de Recherche SW le Pa&d&e, Olgalaisarion de Coordinationpour EaLutte contre desEn&mies en Aj+ique Centrale (UCEAC), BP 288, Yaouna%, Cameroon Keywords: malaria, Plasmodium falciparum, drug resistance, sulfadoxine, Cameroon

chemotherapy,

Plasmodium falciparum ment of chioroquine-resistant infections. Although the drug combination remains generally effective in Central and West Africa, the declining clinical effectiveness of sulfadoxineipyrimethamine reported from East Africa (CURTIS et al., 1998) calls for regular surveillance of drug resistance. Sulfadoxine and pyrimethamine compete with the natural substrates (p-aminobenzoic acid (PABA) and dihydrofolate, respectively) and inhibit the enzymes of the folate biosynthetic pathway, dihydropteroate synthase (DHPS) and dihydrofolate reductase (DHFR), respectively. Resistance of I? falciparum to these antifolate drugs is associated with the substitution of key amino acid residues, Ala437Gly and SerlOBAsn, of DHPS and DHFR,

respectively

Although

Introduction Sulfadoxine/pyrimethamine is currently used in Africa and in some parts ofAsia and South America as either the first-line or second-line antimalarial drug for the treat-

Address for correspondence: Dr Pascal Ringwald, Cluster of Communicable Diseases (CDS), Surveillance and Response (CSR), Anti-infective Drug Resistance Surveillance and Containment (DRS), World Health Organization, 1211 Geneva 27, Switzerland; e-mail ringwaldp@who,ch

(COWMAN,

1997). Additional

ami-

no acid substitutions that confer a higher level of drug resistance have been identified in both DHPS (positions 436, 540, 581, and 613) and DHFR (positions 16, 51, 59, and 164). the sensitivity

pyrimethamine

in vitro

of I? fakiparum

to

alone has been monitored (BASCO 8t NNGWALD, 2000), the activity in z&o of sulfadoxine alone and in combination with pyrimethamine has not been studied extensively in field isolates. The main reason underlying the relative scarcity of sensitivity data in virro for sulfadoxine is the poor solubility of the compound in water at neutral pH or in alcohol. WANG et al. (1997) developed a new assay procedure in V&O to determine the sulfadoxine sensitivity of reference clones of l? fdcapamm.Because of the preponderant position that sulfadoxine occupies in current antimalarial chemo-