Ismael Lares-Asseff

Pharmacokinetics of metronidazole in severely malnourished and nutritionally rehabilitated children

A comparison of the pharmacokinetics of oral metronidazole, after a single dose of 30 mg/kg body weight, was done in two groups of subjects: group I consisted of 10 severely malnourished children, aged 4 to 43 months; group II consisted of 10 children, aged 3 to 25 months, who were studied after nutritional rehabilitation. The biologic half‐life of elimination was significantly longer (p< 0.01) in severely malnourished children (median, 10.21 hours; range, 4.89 to 22.93 hours) than in rehabilitated children (median, 5.09 hours; range, 2.61 to 8.75 hours). Metabolic clearance of metronidazole was significantly lower in group I (p< 0.01; median, 0.077 L/kg/hr; range, 0.033 to 0.192 L/kg/hr) than in nutritionally rehabilitated children (median, 0.166 L/kg/hr; range, 0.105 to 0.300 L/kg/hr). Volume of distribution was not different between groups I and II, although both showed higher values than the values reported for children who were not malnourished. These findings suggest that the dose of metronidazole should be reduced in malnourished children, and the therapeutic regimen should be individualized for each patient.

CYP2D6 genotype and phenotype in Amerindians of Tepehuano origin and Mestizos of Durango, Mexico.

Although the drug‐metabolizing enzyme CYP2D6 has been studied extensively in subjects of differing ethnicities, limited CYP2D6 pharmacogenetic data are available for the Amerindian population and Mestizos of Mexico. Dextromethorphan hydroxylation phenotype was studied in Tepehuano Amerindian (n = 58) and Mestizo (n = 88) subjects, and 195 individuals (85 Tepehuano Amerindians and 110 Mestizos) were genotyped by polymerase chain reaction‐restriction fragment length polymorphism methods to identify the frequencies of the CYP2D6*3, *4, *6, and *10 alleles. Tepehuano Amerindian subjects lacked the poor metabolizer (PM) phenotype, whereas in Mestizos the PM phenotype frequency was 6.8%. The CYP2D6*3, *6, and *10 alleles were not found in Tepehuano Amerindians. The CYP2D6*4 allele had a low frequency (0.006) in this Amerindian group. In the Mestizo group, the CYP2D6*3, *4, and *10 alleles had frequencies of 0.009, 0.131, and 0.023, respectively. The CYP2D6*6 allele was not found in Mestizos. The genotype‐phenotype association was strongly statistically significant (r2 = .45; P = .005) in Mestizos. The Tepehuano population was found to have a low phenotypic and genotypic CYP2D6 diversity and differed from other Amerindian groups. On the other hand, the frequencies of the CYP2D6 variant alleles in Mestizos were similar to those reported for whites.

Influence of CYP2D6 Deletion, Multiplication,-1584C~G, 31G~A and 2988G~A Gene Polymorphisms on Dextromethorphan Metabolism among Mexican Tepehuanos and Mestizos

The aim of this study was to explain the variability of CYP2D6 activity by the identification of CYP2D6 deletion and multiplications, and the single-nucleotide polymorphisms (SNPs) –1584C→G, 31G→A and 2988G→A in Mexican Mestizo and Tepehuano subjects. One hundred twelve Mestizos and 99 Tepehuano Amerindians were studied, who were previously phenotyped with dextromethorphan. The frequencies of CYP2D6*2A [–1584C→G] and *35 [–1584C→G, 31G→A] were 10.7 and 4.1%, respectively, in Mestizos, which is evidently a trend towards an extensive metabolism in carriers of the –1584G change. In Tepehuanos, *2A was identified with a frequency of 20%, and the allele *35 was not found. The frequencies of CYP2D6*5 (deletion) and *41[2988G→A] were 1.3 and 2.2% in Mestizos and 0.5 and 1% in Tepehuanos, respectively. The SNP 2988A was found to be significantly related with the intermediate metabolizer phenotype in Mestizos (R = 0.309; n = 88; p = 0.006). The multiplications had frequencies of 4.1% in Mestizos and 1.5% in Tepehuanos. Only in the Mestizos did the presence of multiplications significantly decrease the DM/DX (dextromethorphan/dextrorphan) values (R = 0.273; n = 88; p = 0.016). The polymorphisms studied had different frequencies between Tepehuanos and Mestizos (p < 0.001); however, in the Tepehuano group these had a low influence on their phenotypic expression. It helps to understand the genotype-phenotype relationships of CYP2D6 in our studied populations.

A New Dosing Regimen for Metronidazole in Malnourished Children

The use of metronidazole for the treatment of intestinal parasitosis has increased markedly, particularly in developing countries, where the association of malnutrition and parasitosis is very common. Since biotransformation of metronidazole is significantly affected by severe malnutrition, and undesirable effects of the drug seem to be related to its plasma concentration, it was decided to carry out a study to establish a dosing-regimen of metronidazole in severely malnourished children. A single dose of 30 mg/kg body weight, and computer simulation of a steady-state was studied in 10 malnourished and in 10 patients undergoing nutritional rehabilitation. Due to ethical considerations (refusal of parents to allow a second dose of metronidazole) acute malnourished children and rehabilitated patients are 2 distinct groups. The results indicate that a predicted drug cumulation would occur in malnourished children with the ordinary dosage regimen (30 mg/kg/day). Based on the clearance data, daily maintenance doses for pediatric patients with severe malnutrition should be 12.0 mg/kg/day, corresponding to a 60% reduction of the common dose calculated to achieve and maintain a plasma concentration of 6.0 micrograms/ml of metronidazole. The study illustrates the need for pharmacokinetic data to establish the individual dose of a drug particularly under conditions that alter biotransformation processes.

Pharmacokinetics of cyclosporine as a function of energy--protein deficiency in children with chronic renal failure.

The present study was conducted to determine whether malnutrition in patients with chronic renal failure requiring cyclosporine therapy for renal transplantation has some effect on the clinical pharmacokinetics of cyclosporine. Eleven pediatric patients were enrolled in this study before renal transplantation and divided into two groups (group I: six well-nourished patients with a deficit in weight/height ratio < or = 7%; group II: five malnourished patients with a deficit in weight/height > 8%). The patients received a single oral dose of cyclosporine (3.0 mg/kg). Blood samples were collected for a 26-hour period, and serum concentrations of cyclosporine were measured using fluorescence-polarization immunoassay technology. The results suggest that, when malnutrition is present, the median Cmax of cyclosporine decreases by almost threefold (from 387.5 ng/mL in group I to 136.1 ng/mL in group II). An observed 52% reduction in AUC0-infinity (from 2,856.0 ng/mL/hr in group I to 1,481.4 ng/mL/hr in group II) was caused by the increased volume of distribution (from 4.6 L/kg in group I to 11.1 L/kg in group II). The elimination half-life (t1/2) was longer in group II compared with that of group I (12.4 hr for group II; range, 7.8-13.5 hr versus 8.9 hr for group I; range, 5.2-16.0 hr). Differences in t1/2 were not statistically significant at 5% confidence intervals. The effects of energy malnutrition on the pharmacokinetics of cyclosporine could explain in part some of the interindividual variability. This study provides pharmacokinetic guidelines for the use of cyclosporine.

Adverse Effects of Imipramine are Increased by Interaction with ASA in Depressed Patients

Because protein binding is a process that can be changed by the presence of other drugs with similar or greater affinity for proteins than the original compound, this causes a greater concentration of the free drug, while potentializing adverse effects, the most important factor responsible for noncompliance (Demyttenaere 1997; Fincke et al. 1998). The purpose of this study was to measure the binding of imipramine to plasma proteins when administered simultaneously with acetyl salicylic acid (ASA). Such interaction would be more clearly defined using clinical assessment parameters in patients treated with imipramine, who additionally need the second drug. The study was carried out in 20 clinically diagnosed depressed patients (16 F, 4 M, average age 38.3 6 13.3 years and weight 63.8 6 9.0 kg) to which imipramine (Tofranil) was administered at doses of 75 mg every 12 h. Informed consent was obtained for all patients before the study. After the first 3 days, while fasting, 6-ml blood samples were taken from the patients and processed. The following were measured: (1) total concentration of the drug in plasma; (2) fraction of imipramine bound to plasma proteins as reported in Juárez and Jung (1986), and protein levels, as indicators of the protein state in the patients studied. Before taking the sample, each patient’s clinical state was assessed using a questionnaire on the possible effects a patient reported, recording the time when the effect arose, its duration, and its severity. This questionnaire was previously validated by the Mental Health Division, Department of the Faculty of Medicine (UNAM). After this first phase, patients took 500 mg of ASA every 12 h for 2 days. At this time, a second sample was taken. The samples were processed, and the parameters as above were assessed. Patients were asked to answer the questionnaire again. The adverse effects were registered and investigation proceedings were carried out by the psychiatry service medical staff at INNN, who had no information about the patients’ treatment. These professionals were well qualified to evaluate the described adverse effects. The degree of binding in patients before the coadministration was 84.4 6 7.07%, and after its administration with the second drug, it was 72.18 6 6.5% ( p , .05, Student’s t -test). The protein levels in all patients were normal. The study confirms that imipramine has a high degree of binding to plasma proteins (Kristensen 1983). When patients were treated with imipramine only, they reported 18 different adverse effects; whereas, after adding the salicylate, the number of adverse effects increased to 28. A parameter confirming the presence of a greater amount of free drug, after the interaction process, was the change in the severity of adverse effects. When patients were treated with imipramine only, 39 effects were expressed as mild, 30 as moderate, and 12 as severe. After the administration of the salicylate, 62 effects were recorded as mild, 31 moderate, and 30 as severe, as shown in Figure 1. No significant increments were seen in the effects classified as moderate. However, in those cases of mild and severe adverse effects, there was a significant increment ( p , .05, Student’s t -test) after administrating the combined drugs. During the analysis of the adverse effects, we found 15 adverse effects that may be common to the levels of imipramine (Petit et al. 1977). However, these effects were found to increase in severity when the amount of free drug increased. The imipramine binding process to plasma proteins may be affected, as in this case, by salicylates as precedent, and studies seem to confirm this process.

Changes in acetylator phenotype over the lifespan in the Wistar rat.

UNLABELLED Acetylation capacity during drug metabolism differs between species, gender and age groups. OBJECTIVE The purpose of this work was to determine variations in the acetylating phenotype (AP), in a longitudinal study, as a function of growth and development. METHODS Twenty male Wistar rats were studied. AP was determined on days 21, 48, 114, 180, 457 and 780 with oral doses of 30mg/kg of sulphadiazine (SDZ) by urine collection. The Schröeder and Vree methods were used to obtain SDZ concentrations, both acetylated and not acetylated. Rats were classified as slow or fast acetylators in accordance with previously validated metabolic indicators. RESULTS Of the 20 rats phenotyped at 21 and 48 days of age, 18 were slow and 2 were fast acetylators. As age and consequent growth progressed, changes in the expression of AP were registered. At 114 days, 16 rats were slow and 4 were fast acetylators; at 180 days, 12 were slow and 8 were fast; at 457 days, 6 were slow and 14 were fast; at 780 days, the 20 rats were fast acetylators. Slow acetylation predominates at younger ages. CONCLUSIONS The effect of growth and developmental progress on AP is evident and relates to previous reports of changes in AP, determined by age in animal and human models. The relevance of changes determined by growth and development should be considered in rational drug management.

Relationship between Clinical and Biologic Variables and Chloramphenicol Pharmacokinetic Parameters in Pediatric Patients with Sepsis

OBJECTIVE: To evaluate the influence of several clinical and biologic factors on the disposition kinetics of oral chloramphenicol in pediatric patients and to determine the usefulness of this information to predict chloramphenicol serum concentrations. STUDY DESIGN: The clinical, biologic, and pharmacokinetic data of 30 consecutive pediatric patients diagnosed with sepsis and admitted to a tertiary care center were analyzed retrospectively. The patients were randomly assigned to a study group and a validation group. The model was developed by a three-step approach involving Bayesian estimation of pharmacokinetic parameters, selection of covariates by principal component analysis, and final selection by stepwise multiple linear regression. The model was tested in the study group and compared with a general population model using a prediction error analysis. RESULTS: Regression analysis revealed that weight, albumin, and white blood cell (WBC) count were the most important determinants for chloramphenicol distribution volume, whereas age, WBC count, and serum creatinine were the most important determinants for chloramphenicol clearance. The performance of the constructed population model improved significantly in terms of both bias and precision compared with the general model when tested in the validation group. CONCLUSIONS: Clinical and biologic factors may significantly influence chloramphenicols disposition in pediatric patients with sepsis and therefore should be considered in programming dosage regimens.

Population Pharmacokinetics of Gentamicin in Mexican Children With Severe Malnutrition.

Background: To develop a population pharmacokinetic model of gentamicin in children with complicated severe malnutrition and to study the influence of covariates (weight and age) on pharmacokinetic indices. In addition, we use the model to perform Monte Carlo simulations to explore the efficacy of several dosage regimens. Methods: Twenty-six children with severe complicated malnutrition were studied. Ninety-six samples of gentamicin plasma concentrations, obtained from 0.5 to 8 hours after intravenous dosing, were analyzed. Population pharmacokinetic models were built using the program Monolix 4.2 (Lixoft, Antony, France). Monte Carlo simulations were performed to evaluate optimal dosage regimens, using the final pharmacokinetic model, based on the probability of pharmacokinetic–pharmacodynamic target attainment. Results: The concentration–time data were fitted best to 1-compartment model. The estimated population clearance was 1.1 L/h, and the volume of distribution was 2.23 L, with an interindividual variability of 47.2% and 35.6%, respectively. The final models for the clearance and volume of distribution were as follows: CL (L/h) = CL = 1.15 (age/median age)0.321 and V (L) = 2.33 (weight/median weight)0.743. In Monte Carlo simulations, gentamicin given in dosages of 7.5 to 15 mg/kg optical density was effective in achieving the pharmacodynamic target Cmax:minimal inhibitory concentration >10 for minimal inhibitory concentrations ⩽2.5 mg/L, with a probability lower than 1% for Cmin >1 mg/L. Conclusions: Based on the available evidence, an intravenous dose of 7.5 to 15 mg/kg once daily in children with complicated severe malnutrition and normal renal function ensures high probability of efficacy and low risk of nephrotoxicity, which gives further support to the recommendations issued by the World Health Organization treatment for this patient population.

Association of ABCB1, ABCC5 and xanthine oxidase genetic polymorphisms with methotrexate adverse reactions in Mexican pediatric patients with ALL.

Abstract Background: Acute lymphoblastic leukemia (ALL) is one of the most frequent oncological disorders in pediatric populations. To date, the drug of choice for the treatment of ALL is methotrexate, a drug associated with a high risk of adverse reactions (ADRs). The xanthine oxidase (XO) polymorphisms, 1936A>G and 2107A>G, as well as the polymorphic variants derived from ATP-binding cassette transporter gene subfamilies, ABCB1 and ABCC5, of drug resistant codifying genes, are implicated as precursors of drug-related neurologic, hepatic, and renal toxicities. Our aim was to determine whether the mentioned polymorphisms are risk or protective factors for the development of adverse reactions by methotrexate in our pediatric population with ALL. Methods: A total of 35 Mexican children from Centro Estatal de Cancerología-Durango, Mexico, with ALL and the previously noted polymorphisms as determined qPCR were studied. At the same time, a 12-month drug monitoring program was conducted in accordance with WHO-PAHO guidelines for pharmacovigilance. Results: The ABCB11936A>G and 2107A>G and ABCC5 3414+434A>C polymorphisms were not associated with methotrexate ADRs. Single nucleotide polymorphisms (SNPs) of ABCB1 1236C>T (OR 0.19, 95% CI: 0.03–0.9, p<0.05) and ABCC5 3933+313T>C (OR 0.12, 95% CI: 0.027–0.58, p<0.05) were associated with methotrexate ADRs. Conclusions: SNPs 1236C>T of ABCB1 and ABCC5 3933+313T>C are not associated with the development of typical ADRs by methotrexate, rather, they showed a protective factor for myelosuppression in the studied sick population.