Iván Saavedra

DDT-dehydrochlorinase—I. Purification and characterization

1. 1. DDT-dehydrochlorinase (E.C. 4.5.1.1) from Musca domestica L. has been purified extensively by ammonium sulfate precipitation, hydroxylapatite adsorption and elution, ethanol precipitation, and Sephadex and DEAE-Sephadex column chromatography. 2. 2. The native enzyme appears to have a molecular weight of 120,000 and it is formed by four monomers of a molecular weight of 30,000 each. 3. 3. Aggregates of monomers to give a molecular weight of 60,000 are inactive. Activity appears only with aggregates of a minimum molecular weight of 90,000. 4. 4. Aggregation of monomers is induced by DDT but not by glutathione, which is required for enzyme activity. However, glutathione prevents dissociation of the enzyme into monomers and polypeptides of lower molecular weights. 5. 5. The mechanism whereby DDT produces aggregation of monomers and glutathione prevents the dissociation of aggregates remains to be established.

Famacogénica del cáncer: Estudio de variaciones genéticamente determinadas en la susceptibilidad a cáncer por exposición a xenobióticos

Pharmacogenetics is the study of genetically determined variations in the response to drugs and toxic agents, and their implications on disease. Recently, the discipline has acquired great relevancy due to the development of non-invasive molecular techniques that identify genetic variants in human beings. There is also a need to explain the individual differences in susceptibility to drug actions and disease risk. Genetic variants can modify the magnitude of a pharmacologic effect, toxicity threshold, secondary effects and drug interactions. There are approximately thirty families of drug-metabolizing enzymes with genetic variants that cause functional alterations and variations in pharmacologic activity. We summarize the general knowledge about genetic variants of biotransformation enzymes, their relationship with cancer risk and the role of ethnicity. Cancer pharmacogenetics is another promising and exciting research area that will explain why people with an almost identical group of genes, have a different susceptibility to cancer, whose etiology has genetic and environmental components.

Phenytoin/clonazepam interaction

An interaction between phenytoin (PHT) and clonazepam (CZP) occurred in an epileptic patient, who had been treated with PHT with partial seizure control. The addition of CZP brought about a significant decrease of PHT plasma levels (from 24.8 to 16 micrograms/ml) in spite of increases in the PHT dose. Gradual reduction of CZP, without modifying the PHT dosage, caused significant increases in PHT plasma levels to 42.4 micrograms/ml with signs of intoxication. A review of the literature shows contradictions: some authors state that there is no interaction between the drugs; other authors state either an increase or decrease in PHT plasma levels. These paradoxical results could be explained by the bidirectional effect of these drugs in hepatic enzyme metabolism. The importance of monitoring plasma levels of antiepileptic drugs is emphasized when several medications are required in the treatment of epilepsy.

A comparative bioavailability study of two formulations of pregabalin in healthy Chilean volunteers

Objective: The aim of this study was to compare the pharmacokinetic parameters between two brands of pregabalin in healthy Chilean volunteers. Methods: A randomized, single-dose, two-period, two-sequence, crossover study design with a 2-week washout period was conducted in healthy Chilean males. Plasma samples were collected over a 12-hour period after administration of 150 mg pregabalin in each period. A validated ultra-performance liquid chromatography with positive ionization mass spectrometric detection method was used to analyze pregabalin concentration in plasma. Pharmacokinetic parameters were determined using a noncompartmental method. Bioequivalence between the test and reference products was determined when the ratio for the 90% confidence intervals (CIs) of the difference in the means of the log-transformed area under the curve (AUC)0-t, AUC0-∞, and maximum concentration (Cmax) of the two products were within 0.80 and 1.25. Results: The study was carried out on 22 healthy Chilean volunteers. The mean (SD) Cmax, AUC0-t and AUC0-∞ of the test formulation (PregobinTM) of pregabalin were 2.10 (0.56) µg/ml, 10.35 (2.00) µgxh/ml and 13.92 (2.74) µgxh/ml, respectively. The mean (SD) Cmax, AUC0-t and AUC0- ∞ of the reference formulation (LyricaTM) of pregabalin were 2.15 (0.52) µg/ml, 10.31 (1.85) µgxh/ml and 13.78 (2.25) µgxh/ml, respectively. The parametric 90% CIs for C max, AUC0-t, and AUC0-∞ were 0.97—1.13, 1.01—1.04, and 0.98—1.02, respectively. Conclusions: These results suggest that both products are bioequivalent and can be used as interchangeable options in the clinical setting.

Bioequivalencia entre dos formulaciones de claritromicina comprimidos de liberación modificada existentes en el mercado chileno

Se realizo un estudio de biodisponibilidad comparativa, para evaluar la bioequivalencia entre dos formulaciones de claritromicina de 500 mg en comprimidos de liberacion modificada, una nacional (Pre-Clar UDO), y el innovador del mercado (Klaricid UDO). Se utilizo un ensayo microbiologico para determinar las concentraciones plasmaticas del antimicrobiano. El ensayo esta basado en la correlacion entre la inhibicion del crecimiento bacteriano y la concentracion plasmatica de claritromicina. Un total de 16 voluntarios, jovenes sanos, no fumadores, participaron y completaron el protocolo del estudio, el cual fue aprobado por el Comite de Etica de la Facultad de Medicina de la Universidad de Chile. Los parametros farmacocineticos de: concentracion plasmatica maxima (Cmax,), tiempo de vida media (t1/2), area bajo la curva de concentraciones plasmaticas versus tiempo desde cero a infinito (ABC0-¥)), constante de velocidad de absorcion (Kabs), no mostraron diferencias estadisticamente significativas entre los productos utilizados. De acuerdo a los criterios recomendados por la FDA y en base a nuestros resultados, se concluye que las formulaciones Pre-Clar UD® y Klaricid UD® son bioequivalentes, asumiendose que tendrian igual eficacia clinica.

Determinación del polimorfismo de CYP2C9*2 y su relación con la farmacocinética de acenocumarol en voluntarios sanos

Resumen:Antecedentes: La mayoria de los pacientes que reciben tratamientos con anticoagulantes orales por periodos prolongados presentan variabilidad en la respuesta. El acenocumarol es el anticoagulante oral mas prescrito en nuestro pais, es biotransformado principalmente por CYP2C9 e investigaciones re-cientes demuestran que la variante CYP2C9*2 es una de las responsables de la variabilidad de res-puesta a acenocumarol. Objetivo: Determinar las diferencias en los para-metros farmacocineticos de acenocumarol en volun-tarios que presentan la variante alelica CYP2C9*2. Metodos: Se estudiaron 24 voluntarios sanos. La deteccion de genotipos se realizo mediante PCR-RFLP y los parametros farmacocineticos se obtuvieron mediante la concentracion plasmatica de acenocumarol usando un metodo validado para UPLC-MS/MS. Resultados: Del total de 24 voluntarios, 19 tenian el genotipo CYP2C9*1/*1 (wt/wt), 4 te-nian genotipo CYP2C9*1/*2 (heterocigoto) y 1 voluntario tenia genotipo de CYP2C9*2/*2 (homocigoto recesivo). Los parametros farma-cocineticos del acenocumarol no fueron signifi-cativamente diferentes entre los individuos con genotipo CYP2C9*2 y CYP2C9*1. Sin embargo, la farmacocinetica de acenocumarol del individuo CYP2C9*2/*2 mostro diferencias relevantes con respecto a la observada en el grupo CYP2C9*1/*1 (tmax aumento 1,4 veces, ke disminuyo 1,8 veces y t1/2 aumento 1,7 veces).

Plasma levels of diphenylhydantoin and the control of adult epileptic seizures: a Chilean experience.

:In a prospective study of 117 adult ambulatory patients, 110 of whom were epileptics treated only with oral diphenylhydantoin (DPH), plasma levels of this drug were determined by gas‐liquid chromatography. The average follow‐up time was 6 months (range, 3 to 13 months); satisfactory control of seizures was obtained with plasma levels in the 10.2 to 25.8 μg/ml range, representing 68% of the patients whose seizures had been controlled. The dosage received by this group was from 4.2 to 6 mg/kg, with an average of 5.1. In general, these results agree with those found in European or North American patients, even though some differences or little clarity in the methodology of other trials make comparison difficult. This similarity of results makes one think that genetic or environmental differences do not alter the response to DPH in our patients, but further studies are necessary in that area. This paper can serve as a basis for the extrapolation of data about DPH coming from other latitudes that have been considered supposedly valid for Latin American epileptic patients.

Bioequivalence of Acenocoumarol in Chilean Volunteers: an Open, Randomized, Double-Blind, Single-Dose, 2-Period, and 2-Sequence Crossover Study for 2 Oral Formulations

The aim of this study was to compare the bioavailability of an oral formulation of the coumarin derivative-vitamine K antagonist acenocoumarol (Acebron™ 4 mg, Test) with the reference formulation (Neo-Sintrom™ 4 mg). We performed a single-dose, double-blind, fasting, 2-period, 2-sequence, crossover study design. Plasma concentrations of acenocoumarol were determined using a validated UPLC-MS/MS method. 24 healthy Chilean volunteers (11 male, 13 female) were enrolled and all of them completed the study. Adverse events were monitored throughout the study. The values of the pharmacokinetic parameters were (mean ± SD): AUC0-24 =1 364.38±499.26 ngxh/mL for the test and 1 328.39±429.20 ngxh/mL for the reference; AUC0-∞ =1 786.00±732.85 ngxh/mL for the test and 1 706.71±599.66 ngxh/mL for the reference; Cmax =180.69±35.11 ng/mL with a Tmax of 1.83±0.95 h for the test and 186.97±38.21 ng/mL with a Tmax of 2.19±0.83 h for the reference. Regarding half life measurements, the mean ± SD of t1/2 were 11.84±4.54 h for the test and 11.08±3.28 h for the reference. The 90% confidence intervals for the test/reference ratio using logarithmic transformed data were 97.89-100.87%, 98.62-101.99% and 98.64-102.38% for Cmax, AUC0-t(24) and AUC0-∞. There were no significant differences in pharmacokinetic parameters between groups.The results obtained in this study lead us to conclude, based on FDA criteria, that the test acenocoumarol formulation (Acebron™, 4 mg tablets) is bioequivalent to the reference product (Neo-Sintrom™, 4 mg tablets).