Single dose disposition of chloroquine in kwashiorkor and normal children--evidence for decreased absorption in kwashiorkor

Influence of Malnutrition on the Pharmacokinetics of Drugs Used in the Treatment of Poverty-Related Diseases: A Systematic Review

Background

Patients affected by poverty-related infectious diseases (PRDs) are disproportionally affected by malnutrition. To optimize treatment of patients affected by PRDs, we aimed to assess the influence of malnutrition associated with PRDs on drug pharmacokinetics, by way of a systematic review.

Methods

A systematic review was performed on the effects of malnourishment on the pharmacokinetics of drugs to treat PRDs, including HIV, tuberculosis, malaria, and neglected tropical diseases.

Results

In 21/29 PRD drugs included in this review, pharmacokinetics were affected by malnutrition. Effects were heterogeneous, but trends were observed for specific classes of drugs and different types and degrees of malnutrition. Bioavailability of lumefantrine, sulfadoxine, pyrimethamine, lopinavir, and efavirenz was decreased in severely malnourished patients, but increased for the P-glycoprotein substrates abacavir, saquinavir, nevirapine, and ivermectin. Distribution volume was decreased for the lipophilic drugs isoniazid, chloroquine, and nevirapine, and the α1-acid glycoprotein-bound drugs quinine, rifabutin, and saquinavir. Distribution volume was increased for the hydrophilic drug streptomycin and the albumin-bound drugs rifampicin, lopinavir, and efavirenz. Drug elimination was decreased for isoniazid, chloroquine, quinine, zidovudine, saquinavir, and streptomycin, but increased for the albumin-bound drugs quinine, chloroquine, rifampicin, lopinavir, efavirenz, and ethambutol. Clinically relevant effects were mainly observed in severely malnourished and kwashiorkor patients.

Conclusions

Malnutrition-related effects on pharmacokinetics potentially affect treatment response, particularly for severe malnutrition or kwashiorkor. However, pharmacokinetic knowledge is lacking for specific populations, especially patients with neglected tropical diseases and severe malnutrition. To optimize treatment in these neglected subpopulations, adequate pharmacokinetic studies are needed, including severely malnourished or kwashiorkor patients.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40262-021-01031-z.

In Vitro Antiviral Activity and Projection of Optimized Dosing Design of Hydroxychloroquine for the Treatment of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2)

Background

The Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) first broke out in Wuhan (China) and subsequently spread worldwide. Chloroquine has been sporadically used in treating SARS-CoV-2 infection. Hydroxychloroquine shares the same mechanism of action as chloroquine, but its more tolerable safety profile makes it the preferred drug to treat malaria and autoimmune conditions. We propose that the immunomodulatory effect of hydroxychloroquine also may be useful in controlling the cytokine storm that occurs late-phase in critically ill SARS-CoV-2 infected patients. Currently, there is no evidence to support the use of hydroxychloroquine in SARS-CoV-2 infection.

Methods

The pharmacological activity of chloroquine and hydroxychloroquine was tested using SARS-CoV-2 infected Vero cells. Physiologically-based pharmacokinetic models (PBPK) were implemented for both drugs separately by integrating their in vitro data. Using the PBPK models, hydroxychloroquine concentrations in lung fluid were simulated under 5 different dosing regimens to explore the most effective regimen whilst considering the drug’s safety profile.

Results

Hydroxychloroquine (EC₅₀=0.72 μM) was found to be more potent than chloroquine (EC₅₀=5.47 μM) in vitro. Based on PBPK models results, a loading dose of 400 mg twice daily of hydroxychloroquine sulfate given orally, followed by a maintenance dose of 200 mg given twice daily for 4 days is recommended for SARS-CoV-2 infection, as it reached three times the potency of chloroquine phosphate when given 500 mg twice daily 5 days in advance.

Conclusions

Hydroxychloroquine was found to be more potent than chloroquine to inhibit SARS-CoV-2 in vitro.

Usefulness of day 7 lumefantrine plasma concentration as a predictor of malaria treatment outcome in under-fives children treated with artemether-lumefantrine in Tanzania

Background

Day 7 plasma lumefantrine concentration is suggested as a predictor for malaria treatment outcomes and a cut-off of ≥ 200 ng/ml is associated with day 28 cure rate in the general population. However, day 7 lumefantrine plasma concentration can be affected by age, the extent of fever, baseline parasitaemia, and bodyweight. Therefore, this study assessed the usefulness of day 7 lumefantrine plasma concentration as a predictor of malaria treatment outcome in under-fives children treated with generic or innovator drug-containing artemether-lumefantrine (ALu) in Tanzania.

Methods

This study was nested in an equivalence prospective study that aimed at determining the effectiveness of a generic ALu (Artefan^®) in comparison with the innovator’s product (Coartem^®). Children with uncomplicated malaria aged 6–59 months were recruited and randomized to receive either generic or innovator’s product. Children were treated with ALu as per World Health Organization recommendations. The clinical and parasitological outcomes were assessed after 28 days of follow up. PCR was performed to distinguish recrudescence and re-infections among children with recurrent malaria. Analysis of day 7 lumefantrine plasma concentration was carried out using a high-performance liquid chromatographic method with UV detection.

Results

The PCR corrected cure rates were 98.7% for children treated with generic and 98.6% for those treated with the innovator product (p = 1.00). The geometric mean (± SD) of day 7 plasma lumefantrine concentration was 159.3 (± 2.4) ng/ml for the generic and 164 (± 2.5) ng/ml for the innovator groups, p = 0.87. Geometric mean (± SD) day 7 lumefantrine plasma concentration between cured and recurrent malaria was not statistically different in both treatment arms [158.5 (± 2.4) vs 100.0 (± 1.5) ng/ml, (p = 0.28) for generic arm and 158.5 (± 2.3) vs 251.2 (± 4.2) ng/ml, (p = 0.24) for innovator arm]. Nutritional status was found to be a determinant of recurrent malaria (adjusted hazardous ratio (95% confidence interval) = 3(1.1–8.2), p = 0.029.

Conclusion

Using the recommended cut-off point of ≥ 200 ng/ml, day 7 plasma lumefantrine concentration failed to predict malaria treatment outcome in children treated with ALu in Tanzania. Further studies are recommended to establish the day 7 plasma lumefantrine concentration cut-off point to predict malaria treatment outcome in children.

Severe Acute Malnutrition Results in Lower Lumefantrine Exposure in Children Treated With Artemether-Lumefantrine for Uncomplicated Malaria

Severe acute malnutrition (SAM) has been reported to be associated with increased malaria morbidity in Sub-Saharan African children and may affect the pharmacology of antimalarial drugs. This population pharmacokinetic (PK)-pharmacodynamic study included 131 SAM and 266 non-SAM children administered artemether-lumefantrine twice daily for 3 days. Lumefantrine capillary plasma concentrations were adequately described by two transit-absorption compartments followed by two distribution compartments. Allometrically scaled body weight and an enzymatic maturation effect were included in the PK model. Mid-upper arm circumference was associated with decreased absorption of lumefantrine (25.4% decreased absorption per 1 cm reduction). Risk of recurrent malaria episodes (i.e., reinfection) were characterized by an interval-censored time-to-event model with a sigmoid maximum-effect model describing the effect of lumefantrine. SAM children were at risk of underexposure to lumefantrine and an increased risk of malaria reinfection compared with well-nourished children. Research on optimized regimens should be considered for malaria treatment in malnourished children.

Pharmacokinetics of hydroxychloroquine and chloroquine during treatment of rheumatic diseases

Hydroxychloroquine (HCQ) and chloroquine (CQ) are well absorbed (0.7-0.8 bioavailability) when given orally. Severe malnutrition (such as kwashiorkor) effects absorption but diahrrea does not. Both HCQ and CQ have prolonged half-lives, between 40 and 50 days, and low blood clearance (e.g. hydroxychloroquine's blood clearance is 96 ml/min). There is great variability of blood concentrations with an eleven-fold range of drug concentrations found after similar doses in RA patients. Protein binding ranges between 30 and 40% with binding to both albumin and alpha1 glycoprotein. There is differential binding and metabolism of the (R) and (S) stereoisomers. Both drugs bind strongly to pigmented tissues but also bind to mononuclear cells, muscles, etc. There is stereo-selective excretion of both drugs and 40-50% of the drug is excreted renally. Between 21 and 47% is excreted unchanged. There is a suggestion of concentration response and concentration toxicity relationships with decreased morning stiffness as HCQ concentrations increase and increased EKG abnormalities as CQ concentrations become higher, but further testing is required. Pharmacokinetic interaction studies are limited. Potentially important kinetic interactions have been documented for d-penicillamine and cimetidine but have not been found for aspirin, ranitidine or imipramine.

Visceral leishmaniasis relapse hazard is linked to reduced miltefosine exposure in patients from Eastern Africa: a population pharmacokinetic/pharmacodynamic study

Background

Low efficacy of miltefosine in the treatment of visceral leishmaniasis was recently observed in Eastern Africa.

Objectives

To describe the pharmacokinetics and establish a pharmacokinetic/pharmacodynamic relationship for miltefosine in Eastern African patients with visceral leishmaniasis, using a time-to-event approach to model relapse of disease.

Methods

Miltefosine plasma concentrations from 95 patients (48 monotherapy versus 47 combination therapy) were included in the population pharmacokinetic model using non-linear mixed effects modelling. Subsequently a time-to-event model was developed to model the time of clinical relapse. Various summary pharmacokinetic parameters (various AUCs, Time > EC₅₀, Time > EC₉₀), normalized within each treatment arm to allow simultaneous analysis, were evaluated as relapse hazard-changing covariates.

Results

A two-compartment population model with first-order absorption fitted the miltefosine pharmacokinetic data adequately. Relative bioavailability was reduced (−74%, relative standard error 4.7%) during the first week of treatment of the monotherapy arm but only the first day of the shorter combination regimen. Time to the relapse of infection could be described using a constant baseline hazard (baseline 1.8 relapses/year, relative standard error 72.7%). Miltefosine Time > EC₉₀ improved the model significantly when added in a maximum effect function on the baseline hazard (half maximal effect with Time > EC₉₀ 6.97 days for monotherapy).

Conclusions

Miltefosine drug exposure was found to be decreased in Eastern African patients with visceral leishmaniasis, due to a (transient) initial lower bioavailability. Relapse hazard was inversely linked to miltefosine exposure. Significantly lower miltefosine exposure was observed in children compared with adults, further urging the need for implementation of dose adaptations for children.

Evaluation of pharmacokinetics of single-dose chloroquine in malnourished children with malaria- a comparative study with normally nourished children

OBJECTIVES

Studies on antimalarial kinetics in children or adults who are undernourished or malnourished are both limited and have yielded conflicting results. The present study was carried out with the objectives of evaluating the pharmacokinetics of single dose chloroquine and its metabolite desethylchloroquine in children who were undernourished and compare them with children who were normally nourished.

METHODS

Children of either gender between the ages of 5 and 12 years, smear positive for P. vivax malaria and classified either as well nourished or undernourished were included. Undernourishment was adjudged based on the Indian Academy of Pediatrics (IAP) classification of protein energy malnutrition [PEM] which in turn was based on Khadilkar's growth charts. All participants received 10 mg/kg on the first day followed by 10 mg/kg on Day 2 and 5 mg/kg on Day 3 along with supportive treatment. Blood samples for the levels of chloroquine [CQ] and desethylchloroquine [DECQ] were collected at 0, 0.5, 1, 2 4, 8, 12, 24, 48, 72 hours and 14 days after the first dose and levels assessed by High Performance Liquid Chromatography.

RESULTS

A total of 12 children who were normally nourished and 13 who were undernourished were studied. Wide inter-individual variability was seen in the levels of both drug and metabolite in both groups of patients. However, the differences in Cmax, AUC 0-inf, Clearance, half life and Vd between the two groups were not significantly different.

DISCUSSION

Our results indicate that dosage requirement is unlikely to be needed for chloroquine in undernourished children with uncomplicated P. vivax malaria.

Efficacy of artemether-lumefantrine in relation to drug exposure in children with and without severe acute malnutrition: an open comparative intervention study in Mali and Niger

BACKGROUND

Severe acute malnutrition (SAM) affects almost all organs and has been associated with reduced intestinal absorption of medicines. However, very limited information is available on the pharmacokinetic properties of antimalarial drugs in this vulnerable population. We assessed artemether-lumefantrine (AL) clinical efficacy in children with SAM compared to those without.

METHODS

Children under 5 years of age with uncomplicated P. falciparum malaria were enrolled between November 2013 and January 2015 in Mali and Niger, one third with uncomplicated SAM and two thirds without. AL was administered under direct observation with a fat intake consisting of ready-to-use therapeutic food (RUTF - Plumpy'Nut®) in SAM children, twice daily during 3 days. Children were followed for 42 days, with PCR-corrected adequate clinical and parasitological response (ACPR) at day 28 as the primary outcome. Lumefantrine concentrations were assessed in a subset of participants at different time points, including systematic measurements on day 7.

RESULTS

A total of 399 children (360 in Mali and 39 in Niger) were enrolled. Children with SAM were younger than their non-SAM counterparts (mean 17 vs. 28 months, P < 0.0001). PCR-corrected ACPR was 100 % (95 % CI, 96.8-100 %) in SAM at both day 28 and 42, versus 98.8 % (96.4-99.7 %) at day 28 and 98.3 % (95.6-99.4 %) at day 42 in non-SAM (P = 0.236 and 0.168, respectively). Compared to younger children, children older than 21 months experienced more reinfections and SAM was associated with a greater risk of reinfection until day 28 (adjusted hazard ratio = 2.10 (1.04-4.22), P = 0.038). Day 7 lumefantrine concentrations were significantly lower in SAM than non-SAM (median 251 vs. 365 ng/mL, P = 0.049).

CONCLUSIONS

This study shows comparable therapeutic efficacy of AL in children without SAM and in those with SAM when given in combination with RUTF, but a higher risk of reinfection in older children suffering from SAM. This could be associated with poorer exposure to the antimalarials as documented by a lower lumefantrine concentration on day 7.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT01958905 , registration date: October 7, 2013.

Theoretical pharmacokinetic drug alterations in pediatric celiac disease

INTRODUCTION

The incidence of pediatric celiac disease has risen and many of these children will receive medications at some time in their life. However, the absorption of drugs in pediatric patients with celiac disease has never been studied. The few studies that do exist have only been performed in adults and indicate that drug concentrations can be altered for some drugs. It is also noteworthy that few researchers have conducted studies to determine if the distribution, metabolism, and excretion of drugs are altered in celiac disease.

AREAS COVERED

The pharmacokinetics of drugs greatly differ between children and adults. Combined with the pathophysiological changes known to occur with celiac disease, there is compelling evidence to support that drug exposure in pediatric celiac disease may be altered. Relevant characteristics of celiac disease that may affect drug disposition include intestinal atrophy, hypoalbuminemia, reduced CYP3A enzymes, and thyroid dysfunction.

EXPERT OPINION

The safety and efficacy of drug dosing in children with celiac disease can be enhanced with additional pharmacokinetic studies of commonly prescribed drugs in this population. Ideally, these studies should include drugs that have high bioavailability, are highly protein bound, undergo extensive CYP3A enzyme metabolism, and/or have a narrow therapeutic range.

A multi-center, open-label trial to compare the efficacy and pharmacokinetics of Artemether-Lumefantrine in children with severe acute malnutrition versus children without severe acute malnutrition: study protocol for the MAL-NUT study

Background

Malnutrition and malaria frequently coexist in sub-Saharan African countries. Studies on efficacy of antimalarial treatments usually follow the WHO standardized protocol in which severely malnourished children are systematically excluded.

Few studies have assessed the efficacy of chloroquine, sulfadoxine-pyrimethamine and quinine in severe acute malnourished children. Overall, efficacy of these treatments appeared to be reduced, attributed to lower immunity and for some antimalarials altered pharmacokinetic profiles and lower drug concentrations. However, similar research on the efficacy and pharmacokinetic profiles of artemisinin-combination therapies (ACTs) and especially artemether-lumefantrine in malnourished children is currently lacking.

The main objective of this study is to assess whether artemether-lumefantrine is less efficacious in children suffering from severe acute malnutrition (SAM) compared to non-SAM children, and if so, to what extent this can be attributed to a sub-optimal pharmacokinetic profile.

Methods/design

In two sites, Ouelessebougou, Mali and Maradi, Niger, children with uncomplicated microscopically-confirmed P. falciparum malaria aged between 6 and 59 months will be enrolled. Two non-SAM children will be enrolled after the enrolment of each SAM case. Children with severe manifestations of malaria or complications of acute malnutrition needing intensive treatment will be excluded.

Treatment intakes will be supervised and children will be followed-up for 42 days, according to WHO guidance for surveillance of antimalarial drug efficacy. Polymerase Chain Reaction genotyping will be used to distinguish recrudescence from re-infection. SAM children will also benefit from the national nutritional rehabilitation program.

Outcomes will be compared between the SAM and non-SAM populations. The primary outcome will be adequate clinical and parasitological response at day 28 after PCR correction, estimated by Kaplan-Meier analysis. To assess the pharmacokinetic profile of lumefantrine, a sparse sampling approach will be used with randomized allocation of sampling times (5 per child). A total of 180 SAM children and 360 non-SAM children will be recruited during the 2013 and 2014 malaria seasons.

Discussion

This study will provide important information that is currently lacking on the effect of SAM on therapeutic efficacy and pharmacokinetic profile of artemether-lumefantrine. If it shows lower therapeutic efficacy and decreased lumefantrine concentrations, it would inform dose optimization studies in SAM children.

Trial registration

ClinicalTrials.gov: NCT01958905

A systematic review of pharmacokinetics studies in children with protein-energy malnutrition

OBJECTIVE

protein energy malnutrition (PEM) is a nutritional problem affecting many children world-wide. Its association with a wide spectrum of infections necessitates multiple drug therapies. A systematic review was performed to determine the effects of PEM on drug pharmacokinetics.

METHODS

literature searches in the MEDLINE and EMBASE databases (January 1960 to December 2009) were performed. Malnutrition, undernutrition, underweight, protein-energy malnutrition, protein-calorie malnutrition, marasmus, marasmic-kwashiorkor or kwashiorkor was the medical subject heading (MeSH) descriptor used. Inclusion criteria were abstracts that assessed or discussed absorption, distribution, metabolism, elimination, clearance, pharmacokinetics or pharmacodynamics of drugs, except micronutrients and appetite-stimulating drugs.

RESULTS

altogether, 41 publications were identified. A total of 34 drugs were studied. The absorption of 18 drugs was studied; the extent of absorption (AUC) was unaffected for 10 drugs. The plasma protein binding of 20 drugs was evaluated; it was significantly reduced for 12 drugs. The volume of distribution (Vd) of 13 drugs was evaluated; it was, however, unaffected for most of the drugs. The effect of PEM on total clearance and the half-life of drugs primarily metabolised by the liver was studied for 8 drugs. There was decreased total clearance and an associated increased half-life of 5 drugs. For 2 drugs (chloramphenicol and quinine), different degrees of PEM affected total clearance differently. The total clearance of six drugs primarily eliminated by the kidneys was studied; it was unaffected for four drugs, but significantly decreased for two drugs (cefoxitin and penicillin).

CONCLUSIONS

considering the proportion of children affected with PEM world-wide, there have been relatively few pharmacokinetic studies of drugs frequently used for their treatment. More studies are therefore required to establish the appropriate dose and safety of these drugs for PEM children. The studies need to recognise that PEM is a disease spectrum and should further look at the differential effects of kwashiorkor and marasmus on drug pharmacokinetics in children.

Pathophysiological changes that affect drug disposition in protein-energy malnourished children

Protein-energy malnutrition (PEM) is a major public health problem affecting a high proportion of infants and older children world-wide and accounts for a high childhood morbidity and mortality in the developing countries. The epidemiology of PEM has been extensively studied globally and management guidelines formulated by the World Health Organization (WHO). A wide spectrum of infections such as measles, malaria, acute respiratory tract infection, intestinal parasitosis, tuberculosis and HIV/AIDS may complicate PEM with two or more infections co-existing. Thus, numerous drugs may be required to treat the patients. In-spite of abundant literature on the epidemiology and management of PEM, focus on metabolism and therapeutic drug monitoring is lacking. A sound knowledge of pathophysiology of PEM and pharmacology of the drugs frequently used for their treatment is required for safe and rational treatment. In this review, we discuss the pathophysiological changes in children with PEM that may affect the disposition of drugs frequently used for their treatment. This review has established abnormal disposition of drugs in children with PEM that may require dosage modification. However, the relevance of these abnormalities to the clinical management of PEM remains inconclusive. At present, there are no good indications for drug dosage modification in PEM; but for drug safety purposes, further studies are required to accurately determine dosages of drugs frequently used for children with PEM.

Reduced efficacy of intermittent preventive treatment of malaria in malnourished children

Intermittent preventive treatment in infants with sulfadoxine-pyrimethamine (IPTi-SP) reduces malaria episodes by 20 to 59% across Africa. This protective efficacy, however, may be affected by the high frequency of malnutrition in African infants. We analyzed the impact of malnutrition as defined by anthropometry on the incidence of malaria and on the protective efficacy of IPTi in a cohort of 1,200 children in northern Ghana, where malaria is hyperendemic. These children received IPTi-SP or placebo at 3, 9, and 15 months of age and were monitored until 24 months of age. Malnutrition was present in 32, 40, and 50% of children at ages 3, 9, and 15 months, respectively. It was associated with increased risks of severe anemia and death but not an increased risk of malaria. Although malaria slightly contributed to chronic malnutrition, IPTi did not substantially improve child growth. Importantly, the protective efficacies of IPTi in malnourished children were roughly half or even less of those observed in nonmalnourished children. In the first year of life, IPTi reduced the incidence of malaria to a significantly lesser extent in infants who received both doses in a malnourished condition (25%; 95% confidence interval [CI], -7 to 48%) compared to that of nonmalnourished children (46%; 95% CI, 30 to 58%; P = 0.049). Moreover, in contrast to nutritionally advantaged children, the rate of severe malaria appeared to be increased in malnourished children who took IPTi. IPTi might exhibit reduced efficacy in regions of abundant malnutrition. Concomitant nutrition programs may be needed in these places to achieve the desired impact.

Chloroquine-treatment failure in northern Ghana: roles of pfcrt T76 and pfmdr1 Y86

Although chloroquine (CQ) monotherapy is now generally inadequate for the treatment of Plasmodium falciparum malaria in northern Ghana--recently, 58% of 225 children failed treatment by day 14--use of the drug continues because of its low cost and wide availability. The risk factors associated with CQ-treatment failure in this region of Africa, including the T76 mutation in the chloroquine resistance transporter (pfcrt) gene and the Y86 mutation in the multidrug resistance (pfmdr1) gene of P. falciparum, have now been investigated, and genotype-failure indices (GFI) have been calculated. Treatment failure was found to be associated with young age, poor nutritional status, pfcrt T76 and pfmdr1 Y86, and early treatment failure (ETF) was also associated with high parasitaemia. The presence and concentration of 'residual' CQ in the blood of patients immediately before they were treated with CQ for the present study appeared to have no effect on outcome. Presence at recruitment of pfcrt T76 or pfmdr1 Y86 or both mutations increased the risk of treatment failure by 3.2-, 2.4- and 4.5-fold, and the risk of ETF by 9.8-, 2.7- and 10.2-fold, respectively. The pfcrt T76 GFI for clinical and all treatment failures were 2.8 and 1.4, respectively. These indices were relatively low in the younger children, those with malnutrition, and those with high parasitaemias when treated. Residual CQ did not affect the GFI substantially. Both pfcrt T76 and, to a lesser extent, pfmdr1 Y86 would be useful tools for the surveillance of CQ resistance in northern Ghana. In the current transition phase to alternative first-line treatment for P. falciparum malaria, it should be possible to provide estimates of the level of CQ resistance by monitoring the prevalences of these mutations.

Biowaiver monographs for immediate release solid oral dosage forms based on biopharmaceutics classification system (BCS) literature data: chloroquine phosphate, chloroquine sulfate, and chloroquine hydrochloride

Literature data on the properties of chloroquine phosphate, chloroquine sulfate, and chloroquine hydrochloride related to the Biopharmaceutics Classification System (BCS) are reviewed. The available information indicates that these chloroquine salts can be classified as highly soluble and highly permeable, i.e., BCS class I. The qualitative composition of immediate release (IR) tablets containing these Active Pharmaceutical Ingredients (APIs) with a Marketing Authorization (MA) in Belgium (BE), Germany (DE), Finland (FI), and The Netherlands (NL) is provided. In view of these MA's and the critical therapeutic indication of chloroquine, it is assumed that the registration authorities had evidence that these formulations are bioequivalent to the innovator. It is concluded that IR tablets formulated with these excipients are candidates for a biowaiver.

Clinical pharmacokinetics and metabolism of chloroquine. Focus on recent advancements

This paper presents the current state of knowledge on chloroquine disposition, with special emphasis on stereoselectivity and microsomal metabolism. In addition, the impact of the patient's physiopathological status and ethnic origin on chloroquine pharmacokinetics is discussed. In humans, chloroquine concentrations decline multiexponentially. The drug is extensively distributed, with a volume of distribution of 200 to 800 L/kg when calculated from plasma concentrations and 200 L/kg when estimated from whole blood data (concentrations being 5 to 10 times higher). Chloroquine is 60% bound to plasma proteins and equally cleared by the kidney and liver. Following administration chloroquine is rapidly dealkylated via cytochrome P450 enzymes (CYP) into the pharmacologically active desethylchloroquine and bisdesethylchloroquine. Desethylchloroquine and bisdesethylchloroquine concentrations reach 40 and 10% of chloroquine concentrations, respectively; both chloroquine and desethylchloroquine concentrations decline slowly, with elimination half-lives of 20 to 60 days. Both parent drug and metabolite can be detected in urine months after a single dose. In vitro and in vivo, chloroquine and desethylchloroquine competitively inhibit CYP2D1/6-mediated reactions. Limited in vitro studies and preliminary data from clinical experiments and observations point to CYP3A and CYP2D6 as the 2 major isoforms affected by or involved in chloroquine metabolism. In vitro efficacy studies did not detect any difference in potency between chloroquine enantiomers but, in vivo in rats, S(+)-chloroquine had a lower dose that elicited 50% of the maximal effect (ED950) than that of R(-)-chloroquine. Stereoselectivity in chloroquine body disposition could be responsible for this discrepancy. Chloroquine binding to plasma proteins is stereoselective, favouring S(+)-chloroquine (67% vs 35% for the R-enantiomer). Hence, unbound plasma concentrations are higher for R(-)-chloroquine. Following separate administration of the individual enantiomers, R(-)-chloroquine reached higher and more sustained blood concentrations. The shorter half-life of S(+)-chloroquine appears secondary to its faster clearance. Blood concentrations of the S(+)-forms of desethylchloroquine always exceeded those of the R(-)-forms, pointing to a preferential metabolism of S(+)-chloroquine.

Pharmacokinetics of quinine, chloroquine and amodiaquine. Clinical implications

Malaria is associated with a reduction in the systemic clearance and apparent volume of distribution of the cinchona alkaloids; this reduction is proportional to the disease severity. There is increased plasma protein binding, predominantly to alpha 1-acid glycoprotein, and elimination half-lives (in healthy adults quinine t1/2z = 11 hours, quinidine t1/2z = 8 hours) are prolonged by 50%. Systemic clearance is predominantly by hepatic biotransformation to more polar metabolites (quinine 80%, quinidine 65%) and the remaining drug is eliminated unchanged by the kidney. Quinine is well absorbed by mouth or following intramuscular injection even in severe cases of malaria (estimated bioavailability more than 85%). Quinine and chloroquine may cause potentially lethal hypotension if given by intravenous injection. Chloroquine is extensively distributed with an enormous total apparent volume of distribution (Vd) more than 100 L/kg, and a terminal elimination half-life of 1 to 2 months. As a consequence, distribution rather than elimination processes determine the blood concentration profile of chloroquine in patients with acute malaria. Parenteral chloroquine should be given either by continuous intravenous infusion, or by frequent intramuscular or subcutaneous injections of relatively small doses. Oral bioavailability exceeds 75%. Amodiaquine is a pro-drug for the active antimalarial metabolite desethylamodiaquine. Its pharmacokinetic properties are similar to these of chloroquine although the Vd is smaller (17 to 34 L/kg) and the terminal elimination half-life is 1 to 3 weeks.

Antimalarial 4-aminoquinolines: mode of action and pharmacokinetics

In the last ten years, the widespread increase in Plasmodium falciparum resistance to chloroquine has prompted research into antimalarial 4-aminoquinolines, empirically used up to now. The mechanism of action of 4-aminoquinolines is characterized by the concentration of the drug in the digestive vacuole of the intraerythrocytic parasite. Various hypotheses have been advanced to explain the specificity of action on the parasite; the most recent one is the inhibition of the haem polymerase of the parasite, leading to the accumulation of soluble haem toxic for the parasite. Chloroquine-resistant parasites accumulate the drug to a lesser extent than do sensitive parasites. Recent findings have shown that chloroquine resistance can be reversed by various tricyclic drugs, which are able to restore the effective concentrations of chloroquine in the infected erythrocyte, but intrinsic mechanisms of action of these reversing agents are unknown. Four-aminoquinolines are extensively distributed in tissues and characterized by a long elimination half-life. Despite similarities in their chemical structures, these drugs show differences in their biotransformation and routes of elimination: chloroquine is partly metabolized into a monodesethylderivative and eliminated mainly by the kidney. In contrast, amodiaquine is a prodrug and amopyroquine is poorly metabolized; both drugs are excreted mainly in the bile. The understanding of the pharmacokinetics of 4-aminoquinolines has led to an improvement in empirically defined therapeutic regimens. Finally, the emergence of severe adverse-effects after prolonged prophylaxis with amodiaquine and the lack of cross resistance of Plasmodium falciparum between chloroquine and amopyroquine, have led to a proposal for the use of intramuscular amopyroquine as an alternative for the treatment of chloroquine-resistant malaria.

Altered pharmacokinetics and dynamics of apomorphine in the malnourished rat: modeling of the composed relationship between concentration and heart-rate response

The impact of malnutrition on the pharmacokinetics and pharmacodynamics (change in heart rate) of apomorphine was studied in the rat. One group of rats received a low-protein diet (0.5%) ad libitum to produce prekwashiorkor. The control group received commercial food pellets. In the first experiment, the two groups received a 2 mg/kg iv bolus dose of apomorphine to determine any differences in the basic pharmacokinetic parameters. The pharmacodynamic characteristics in each group were studied at different steady-state plasma levels, achieved by iv infusions with continuous measurements of the heart rate. There was an almost twofold decrease in the plasma clearance in the malnourished rats compared with controls. A pronounced change in the pharmacodynamic response was also observed in the malnourished group. In the control group, apomorphine produced bradycardia at low concentrations and tachycardia at high concentrations, while only bradycardia was registered in the malnourished group, with maximum effects at steady-state plasma concentrations of 50 ng/ml and a return to baseline at higher concentrations. The effects in control and malnourished rats were fitted simultaneously to the sum of two Hill equations with a nonlinear regression program, and the fits were compared by means of an F test. The maximum pure tachycardia obtainable differed significantly in the prekwashiorkor group compared to the control group. These results suggest a selective down regulation/desensitization only of the receptors responsible for the tachycardia produced by apomorphine during malnutrition.

Pharmacokinetics of quinine in African children suffering from kwashiorkor

The pharmacokinetics of quinine were studied in seven normal African children and in six African children suffering from kwashiorkor, after an oral dose of 10 mg kg-1 of quinine hydrochloride. The two groups were similar in age but the children with kwashiorkor weighed significantly less than the control children (P less than 0.001). The children with kwashiorkor further differed from the control children in having significantly lower packed cell volume (P less than 0.001), total plasma protein and plasma albumin (P less than 0.001), and higher serum SGOT (P less than 0.05). The apparent absorption half-life was significantly longer in kwashiorkor than in controls (P less than 0.05). Similarly, the Cmax was significantly lower (P less than 0.01) in kwashiorkor than in controls. Quinine was eliminated more slowly in children with kwashiorkor, the elimination half-life being significantly longer (P less than 0.001) and the oral clearance significantly less (P less than 0.001) than in controls. It is concluded that kwashiorkor significantly affects the pharmacokinetics of quinine, and that the effect may be due to the pathological changes in the intestine and liver in this condition.

Drug metabolism and pharmacokinetics in malnourished children

Malnutrition is a complex condition in which many deficiencies occur simultaneously. Protein-energy malnutrition is a major public health and clinical problem in paediatric practice that accounts for high child mortality and morbidity. It includes many different clinical syndromes with protean manifestations. The malnourished often have several concomitant diseases; drugs are therefore as widely used as in the well-nourished. The pathophysiological profile in malnutrition can alter pharmacokinetic processes, drug responses and toxicity. This review summarizes the available knowledge on nutrient-drug interactions in malnourished children. Although there is much evidence in the literature that diet and nutritional status are 2 important environmental variables determining the pharmacotoxicological properties of chemicals, there are few data on humans. Recently, intense effort has been initially directed at studying drug kinetics in grade III malnutrition, namely kwashiorkor and marasmus. Studies on drugs and nutrients indicate delayed or decreased absorption, reduced protein binding of several drugs, fluctuations in volume of distribution, altered hepatic oxidative drug biotransformations and conjugations, reduced elimination of conjugates and reduced elimination of renally excreted drugs. The estimated steady-state levels of a few drugs suggest accumulation. Bioavailability problems with certain drugs are due to divergent effects of pharmacokinetic processes. Clinical risk of toxicity appears to be higher in malnourished children. Rehabilitation studies suggest that a number of these pharmacological abnormalities can be reversed. The majority of studies have concentrated on single-dose pharmacokinetics in severely malnourished children. A number of abnormalities seen in drug disposition during the acute phase of malnutrition need to be confirmed for other grades of malnutrition. For practical purposes, it is important to consider steady-state levels and data in mild and moderate forms of growth-retarded children; drug-induced nutritional deficiencies can occur more easily in these populations. Although some of the drugs described in this review have been in use for many years, knowledge on drug response and toxicity is still only approximate. There is at present enough evidence to support monitoring plasma drug concentrations in malnourished children, particularly for those drugs which have dose-dependent kinetics and narrow margins of safety. The metabolism and disposition of xenobiotics seem to vary widely in children with protein-energy malnutrition. Therapeutic inadequacies and toxicities need careful evaluation in malnourished children.

Influences of diet and nutrition on clinical pharmacokinetics

The human diet represents a complex and variable mixture of nutrients, many of which have the potential for altering the disposition of drugs. This review highlights progress from a number of laboratories illustrating nutrient influences on drug dispositions and actions. Emphasis is placed on nutritional effects on hepatic drug metabolism studied in humans. Data from animals have sometimes been difficult to extrapolate to humans, as illustrated by reports on the influences of starvation, dietary lipids, and ascorbic acid. From studies in healthy subjects it is now clear that a number of specific dietary factors can influence drug metabolism by the mixed function oxidase system and conjugating enzymes. These include dietary protein, cruciferous vegetables, charcoal-broiled beef containing polycyclic aromatic hydrocarbons, and methylxanthines. The effects of such dietary components have been demonstrated for only a limited number of drug substrates for these enzyme systems. Effects of food on bioavailability have been more widely studied, and depend greatly upon the type of drug. Malnutrition can be associated with variable but potentially important effects on the bioavailability, binding, hepatic metabolism, and renal clearance of drugs. In malnourished patients it is generally difficult to recognise the roles of individual nutrient deficiencies on drug disposition, and clinical predictors of altered pharmacokinetics for various drugs in such patients are not well defined. It is likely that many important interrelationships between nutrition and new or already marketed drugs remain to be recognised, and therefore warrant further research. Nutritional effects on drug metabolising enzymes also have implications for endogenous substances such as hormones and environmental toxins and carcinogens which are metabolised by the same or related enzyme systems, and for diseases likely to be related to the actions of such chemicals.