Time-kill and post-antibiotic effect of colistin at different static concentrations in in vitro Acinetobacter baumannii

@# Nosocomial infection caused by Acinetobacter baumannii is common among immunocompromised patients. Treatment strategy is limited due to rapid resistance development and lack of novel antibiotic. Colistin has been the last line therapy with good in vitro activity against infections caused by multi-drug resistance A. baumannii. However, pharmacological updates are required to support dosing optimisation. This study aimed to determine the time-kill kinetic and resistance development after antibiotic exposure as well as post-antibiotic effect of colistin at different static concentrations in in vitro A. baumannii system. The static in vitro time-kill and post-antibiotic effect experiments were conducted against two clinical isolates as well as one reference isolate ATCC 19606. Time-kill and postantibiotic effect were studied at colistin concentrations ranging from 0.25MIC to 16.0MIC and 0.5MIC to 4.0MIC, respectively. Post-exposure resistance development was examined in time-kill study. Killing activity and post-antibiotic effect were in a concentration-dependent manner. However, delayed killing activity indicates colistin tolerance. Development of resistance after exposure was not detected except for the ATCC 19606 strain. Dosing suggestion based on the observations include administration of supplemental dose 3 MIU at 12 hours after loading dose, administration of maintenance dose 9 MIU in two divided doses and application of extended interval in renal adjustment dose. However, the information is applicable for non-colistin-heteroresistance A. baumannii with colistin MIC < 1.0 mg/L. As for heteroresistance and strain with colistin MIC > 1.0 mg/L, combination therapy would be the more appropriate treatment strategy.

[Behavior of neonates with hyperbilirubinemia treated with blue light]. / Chováni novorozencu s hyperbilirubinémii lécených modrým svetlem.

Two groups of fullterm newborns were polygraphically examined. The first group consisted of 10 newborns with hyperbilirubinemia treated by phototherapy, the second group was a control one and consisted also of 10 newborns. The polygrams were made at the age of four days. The length of the sleep cycle, the length of quiet and paradoxical sleep, respiratory rate during both sleep states, the frequency of rapid eye movements during paradoxical sleep, the frequency of EMG discharges during paradoxical sleep, the number of sleep apneas during paradoxical sleep and the incidence of body movements during the whole recording time (100 minutes) were assessed. There were no significant differences in majority of parameters, only the length of paradoxical sleep and the number of sleep apneas were significantly higher in infants with hyperbilirubinemia. Infants with higher levels of bilirubin had longer sleep cycle, longer paradoxical sleep and lower incidence of body movements. Large individual differences in all parameters studied were observed, especially in infants with hyperbilirubinemia. This indicates that special observational care should be given to these infants.

[Photoisomers of bilirubin in the blood of neonates during phototherapy]. / Fotoizoméry bilirubinu v krvi novorozencu pri fototerapii.

In a group of mature neonates with hyperbilirubinaemia the authors investigated by chromatography, using the HPLC method, levels of bilirubin photoisomers before phototherapy, in the course of phototherapy and after its termination. The configuration isomer 4 Z, 15 E is detected in blood of all icteric neonates already before the onset of treatment in a mean concentration of 5.2 (s = 3.8) mumol/l, during phototherapy its mean concentration is 23.0 (s = 8.0) mumol/l. Photoisomers participate in non-conjugated bilirubinaemia on average by 10%: 92% are formed by isomer 4 Z, 15 E, 5% by isomer 4 E, 15 Z and 3% by the structural isomer lumirubin. On the day following discontinuation of treatment the mean photoisomer concentrations are significantly lower than during phototherapy and significantly higher than before its initiation.

Study of the mechanism of the photoisomerization and photooxidation of bilirubin using a model for the phototherapy of hyperbilirubinemia.

Liquid chromatography was employed for a study of photochemical degradation of bilirubin in the complex with human albumin, using a model system in the presence of riboflavin. The concentrations of bilirubin, the photoisomers and biliverdin were monitored. The reaction mechanism was verified using a quantified mathematical model and was represented by a reaction scheme. Photoisomerization is the initial process, followed by photooxidation to degradation products of the tetrapyrrole skeleton, with formation of biliverdin as an intermediate. The blood of newborns that were irradiated for treatment of hyperbilirubinemia was studied for the sake of comparison. The effect of some biochemically important substances was followed, in view of possible inhibition of the processes. The experimental results demonstrate that riboflavin acts as a catalyst, even at the concentrations typical for its occurrence in blood. The results are discussed from the point of view of the mechanism of bilirubin degradation during phototherapy.

[Transcutaneous measurement of the severity of icterus and bilirubinemia in normal neonates]. / Transkutánní merení intenzity ikteru a bilirubinémie fyziologických novorozencu.

Using a Minolta/Air Shields apparatus, the authors made 1040 transcutaneous estimations of the intensity of jaundice and examined at the same time the serum bilirubin in 603 normal mature neonates. They revealed a significant (P less than 0.001) correlation between the results of this estimation on the sternum and bilirubinaemia (r = 0.75). Based on the assessment of the 95% confidence limit of prediction of linear regression the authors defined and confirmed by statistical calculations for bilirubinaemia values of 200, 250 and 300 mumol/l four grades of intensity of jaundice. By the suggested procedure omission of early indication of laboratory examination and phototherapy is reduced to a minimum and conversely it is possible to avoid in some neonates collection of blood samples for laboratory examination.

[Alpha-fetoprotein in umbilical cord blood and hyperbilirubinemia in normal neonates]. / Alfa-fetoprotein v pupecníkové krvi a hyperbilirubinémie fyziologických novorozencu.

In a group of 154 mature normal neonates the authors recorded significantly higher mean alpha-fetoprotein values in children with hyperbilirubinaemia (higher than 205 mumol/l) than in other neonates. The differences were observed also in children of equal gestation age. Development of hyperbilirubinaemia is more probable and indication for phototherapy is significantly higher in neonates with alpha-fetoprotein levels in umbilical blood above 100 mg/l and these infants must be carefully observed. When the concentration is above 130 mg/l, the development of hyperbilirubinaemia may be assumed with certainty. Examination of alpha-fetoprotein in umbilical blood is an useful indicator of the functional maturity of the liver, but does not ensure reliable prediction of hyperbilirubinaemia in individual neonates. A concentration of alpha-fetoprotein above 100 mg/l is exceptional among neonates without hyperbilirubinaemia, while lower values do not rule out the development of hyperbilirubinaemia.

[Results of phototherapy in neonatal hyperbilirubinemia using green and blue light]. / Výsledky fototerapie novorozeneckých hyperbilirubinémií zeleným a modrým svetlem.

In a group of normal newborns with birth weights of 2500 g and more treated on account of hyperbilirubinaemia the authors recorded a significantly shorter period of decline of serum bilirubin in 40 children with blue light phototherapy than in 40 children with green light phototherapy. The period of decline of bilirubinaemia with green light phototherapy did not differ on average from the period of spontaneous decline recorded in a group of 40 normal neonates with untreated hyperbilirubinaemia.

[The effect of blue light on the behavior of neonates]. / Vliv modrého svetla na chování novorozencu.

In ten healthy neonates the influence of blue light was analyzed, using polygraphy. In each child the polygrams were assessed under two conditions--without irradiation and without irradiation. The length of the sleep, cycle, the length of quit and paradoxical sleep, the respiration rate during both behavioural states, the frequency of rapid eye movements during paradoxical sleep, the incidence of EEG activity corresponding to age and the EMG activity during both behavioural states did not change significantly under the influence of light. Only the number of apnoeic intervals during paradoxical sleep under blue light increased significantly. The authors assessed, using polygraphy, also a control group of ten healthy mature neonates. The two groups of children did not differ significantly in the investigated parameters. The results revealed a great inter- and intraindividual variability which suggests the low stability of the child's behaviour during the first days of life. Among the numerous stimuli of the external and internal environment which modify the behaviour during the period of postpartum adaptation, the influence of blue light did not play a significant role under the above conditions.

[Hyperbilirubinemia in normal neonates]. / Hyperbilirubinémie fyziologických novorozencu.

In a group of 13,449 neonates with a birth weight of 2500 g or more and without an incompatible constellation with the mothers in the Rh and ABO system in 17.7% of the children a rise od serum bilirubin above 205 mumol/l was found and 5.3% of the children were treated by phototherapy. The frequency of hyperbilirubinaemias and phototherapy in the course of the ten-year investigation rose significantly. Among neonates with hyperbilirubinaemia and those having phototherapy boys predominate significantly. The development of serum bilirubin levels differs as to the course, maximum value and period of the peak and suggests that also in normal mature neonates the rate of adaptation of the bilirubin metabolism displays great individual variations.

ABO haemolytic disease: sex ratio and blood groups in the newborns requiring treatment.

In our group of newborns we have observed that the rate of occurrence of incompatibility states between blood group 0 mothers and their blood group A or B offspring amounted to 14%. It was in every tenth newborn that this incompatibility became manifest as a haemolytic disease requiring treatment. There were no significant differences between blood group A or B newborn infants, either in the frequency rates of hyperbilirubinaemia or in the uniformly indicated therapeutical measures. Among the neonates treated successfully by phototherapy boys prevailed significantly. In contrast, among the most severe forms of the ABO haemolytic disease, requiring blood exchange transfusion, there was a significantly higher prevalence of girls. In relationship to the time of institution of phototherapy as a method of treatment, there occurred a significant decrease of the rates of newborns treated by exchange transfusion. This was due specially to a significant decrease of the necessity of performing this procedure in blood group A boys.

Metabolism of bilirubin and riboflavin in the course of phototherapy for hyperbilirubinaemia in the newborns.

The study of bilirubin photochemical degradation in the presence of riboflavin has shown that, in this case, the primary process is photooxidation during which riboflavin acts as a receptor and bilirubin as a donor of electrons. The reaction proceeds under anaerobic conditions in an equilibrated manner, under aerobic ones as a catalytic process during which the catalyst, i. e., riboflavin is regenerated. The primary intermediate product is biliverdin in vitro, later this is further broken down. For the purpose of studying the mechanism of this process liquid chromatography and computerized technique based on solving nonlinear differential equations have been used. It appears that during phototherapy in the newborn infant there develops a decrease of the blood level of riboflavin reaching up to hypovitaminotic values and a transient biliverdin level elevation. Oral riboflavin administration may maintain this level within physiological range and at the same time shorten the necessary duration of phototherapy. In severe cases of hyperbilirubinaemia a shift of the ratio between flavin-adenin-dinucleotide and free riboflavin, as compared to the physiological state, has been recorded. The results of this work are discussed in the light of our current knowledge concerning the mechanisms of bilirubin breakdown during prototherapy.

Study of the mechanism of the photochemical oxidation of bilirubin by high-performance liquid chromatography.

The photochemical degradation of bilirubin was studied in vitro using high-performance liquid chromatography and spectrophotometry. Attention was centered on the formation of biliverdin, which is produced as an intermediate in the photooxidation catalysed by riboflavin. approximate values of the overall and partial relative rate constants were calculated using the physiochemical criteria for a pseudo-monomolecular reaction. A more precise evaluation was made by non-linear regression programmes on a Hewlett-Packard 9835 A computer. In addition to the formation of biliverdin, attention was also paid to accompanying processes affecting the reaction mechanism, which were explained as aggregation and dimerization of bilirubin and biliverdin. It was also found that during phototherapy of newborn babies suffering from hyperbilirubinaemia the level of biliverdin in the plasma increased. The results are discussed from the point of view of phototherapy.