Hepatic drug clearance in children: studies with indocyanine green as a model substrate

Identification of Pediatric Tumors Intraoperatively Using Indocyanine Green (ICG)

BACKGROUND

Fluorescence-guided surgery (FGS) with indocyanine green (ICG) is increasingly applied in pediatric surgical oncology. However, FGS has been mostly reported in case studies of liver or renal tumors. Applying novel technologies in pediatric surgical oncology is more challenging than in adult surgical oncology due to differences in tumor histology, biology, and fewer cases. No consensus exists on ICG-guided FGS for surgically managing pediatric solid tumors. Therefore, we reviewed the literature and discuss the limitations and prospects of FGS.

METHODS

Using PRISMA guidelines, we analyzed articles on ICG-guided FGS for childhood solid tumors. Case reports, opinion articles, and narrative reviews were excluded.

RESULTS

Of the 108 articles analyzed, 17 (14 retrospective and 3 prospective) met the inclusion criteria. Most (70.6%) studies used ICG to identify liver tumors, but the timing and dose of ICG administered varied. Intraoperative outcomes, sensitivity and specificity, were reported in 23.5% of studies. Fluorescence-guided liver resections resulted in negative margins in 90-100% of cases; lung metastasis was detected in 33% of the studies. In otolaryngologic malignancies, positive margins without fluorescence signal were reported in 25% of cases. Overall, ICG appeared effective and safe for lymph node sampling and nephron-sparing procedures.

CONCLUSIONS

Despite promising results from FGS, ICG use varies across the international pediatric surgical oncology community. Underreported intraoperative imaging outcomes and the diversity and rarity of childhood solid tumors hinder conclusive scientific evidence supporting adoption of ICG in pediatric surgical oncology. Further international collaborations are needed to study the applications and limitations of ICG in pediatric surgical oncology.

Pharmacokinetics of oral vinorelbine in French children with recurrent or progressive primary low-grade glioma

AIM

There is a crucial need for pharmacokinetic (PK) data of oral vinorelbine (VNR) in pediatric population. The aim of this work was to assess the PK profile of orally administered VNR in children with recurrent/progressive primary low-grade glioma (LGG).

METHODS

A multicentric, open-label, single-arm intervention phase II study was conducted. Patients, aged between 6 and 18 years, with histologically confirmed recurrent or progressive primary LGG or non-documented typical optic pathway tumors, were included. PK parameters were estimated by non-compartmental analysis using Phoenix WinNonlin® software (version 8.0, Certara, Inc.). The Influence of demographic and biological covariates on VNR PK parameters was investigated using a multivariate linear regression analysis.

RESULTS

PK analysis included 36 patients with a median age (range) of 11 (6-17) years. Estimates of apparent oral clearance (CL/F), apparent volume of distribution (V/F), half-life (t_1/2 ) and their between-subject variability (CV%) at 60 mg.m^-2 dose level, were 472 L.h^-1 (51.8%), 7002 L (57.9%) and 10 h (21.0%), respectively. Negligible accumulation of VNR between C1 and C2 was observed. CL/F and V/F were found to increase with body surface area (BSA) (p = 0.004). Lower area under the concentration-time curve (AUC) levels were observed among children in comparison to adults.

CONCLUSION

Higher doses may be necessary for children with LGG. BSA showed a significant impact on VNR systemic exposure. We believe that our findings will serve as a basis for further studies to better characterize the concentration-response relationships of VNR among pediatric patients.

Indocyanine Green-Guided Pediatric Tumor Resection: Approach, Utility, and Challenges

Incomplete tumor resection increases the risk of local recurrence. However, the standard of care approach to distinguishing tumor tissue is less than optimal, as it depends on a conglomeration of preoperative imaging and visual and tactile indicators in real time. This approach is associated with a significant risk of inadequate resection; therefore, a novel approach that delineates the accurate intraoperative definition of pediatric tumors is urgently needed. To date, there is no reliable method for the intraoperative assessment of tumor extent and real-time differentiation between tumor- involved tissues and tumor-free tissues. Use of intraoperative frozen sections is challenging, time consuming, and covers a small surface area. Increased vascular permeability and impaired lymphatic drainage in the tumor microenvironment leads to an enhanced permeability and retention effect of small molecules. ICG is a fluorescent dye that when administered intravenously accumulates passively in the tumor because of EPR, thereby providing some tumor contrast for intraoperative real-time tumor recognition. Preclinical and clinical studies suggest that the tumor-to-background fluorescence ratio is optimized when imaging is obtained 24 h after dye injection, and many studies suggest using a high dose of ICG to optimize dye retention in the tumor tissue. However, in childhood cancers, little is known about the ideal dosing, applications, and challenges of ICG-guided tumor resection. This retrospective study examines the feasibility of ICG-guided tumor resection in common childhood solid tumors such as neuroblastoma, sarcomas, hepatic tumors, pulmonary metastases, and other rare tumors. Pediatric dosing and challenges related to the optimization of tumor-to-background ratio are also examined.

Intravenous Thrombolysis at 3.5 Hours From Onset of Pediatric Acute Ischemic Stroke

Acute thrombolysis has a proven benefit for adults presenting with acute ischemic stroke, but data within the pediatric population are extremely limited. We report the case of a 14-year-old girl who presented with right-sided weakness and ataxia, loss of sensation, and altered mental status. Magnetic resonance imaging with diffusion-weighted imaging showed an acute lesion in the distribution of the left posterior cerebral artery, and magnetic resonance angiogram demonstrated occlusion of the third branch of the left posterior cerebral artery. With parental consent, clinicians decided to infuse an adult dose of weight-adjusted intravenous alteplase at 3.5 hours from onset of symptoms, with subsequent improvement in National Institutes of Health Stroke Scale score from 11 to 3. Computed tomography angiogram at 24 hours showed recanalization of the occluded vessel with no evidence of intracranial hemorrhage. Stroke Scale score at discharge was 3, with modified Rankin Scale scores at discharge of 1 and at 90 days of 0. This case highlights the importance of magnetic resonance imaging in diagnosing pediatric acute ischemic stroke and suggests consideration of thrombolysis in select confirmed pediatric stroke cases. However, a rigorous evidence base is lacking, and clinical trials have not been successful in recruiting patients.

Clearance of Indocyanine Green in Severe Pediatric Burns

BACKGROUND

Clearance of indocyanine green dye (ICGc) reflects sinusoidal perfusion and hepatocyte cell membrane function. Thus, ICGc is a reflection of the functional reserve of intact hepatocytes. The purpose of this study was to identify predictors of ICGc in severely burned children during the acute hospitalization and at the time of discharge from the intensive care unit (ICU). A secondary aim was to determine the relationship between liver size and patient ICGc.

METHODS

Twenty-six children (0.8-17 years old) with 35% or greater total body surface area burned (%TBSA-B) were included. Assessment of ICGc (in milliliters per minute per meter squared) was done during the acute hospitalization (median: 6 days after admission, median: 14 days postburn) and at the time of discharge from the ICU (median: 19 days after admission, median: 27 days postburn). Age, TBSA-B, % third-degree burns, inhalation injury, preexisting chronic malnutrition, hematocrit, liver dysfunction, and time from burn injury were incorporated in multiple linear regressions as predictive variables of ICGc. Only variables with p < 0.05 were retained in the final models.

RESULTS

Time from injury and age were the strongest predictors of ICGc during the acute admission but not at the time of discharge from the ICU. Time from injury was negatively associated with ICGc, whereas age was positively associated. At the time of discharge from the ICU, ICGc was increased in proportion to the %TBSA-B, whereas inhalation injury and preexisting chronic malnutrition were associated with lower ICGc. There was no correlation between change-to-predicted liver length and ICGc.

CONCLUSIONS

The intrinsic ability of the liver to extract ICG from plasma was lower in younger burned patients during the acute admission and in those with preexisting chronic malnutrition and inhalation injury at the time of discharge from the ICU.

LEVEL OF EVIDENCE

Prognostic/Epidemiologic, level III.

Mechanical thrombectomy in children and adolescents: report of five cases and literature review

Background

Paediatric arterial ischaemic stroke is an important cause of morbidity and mortality among children. Currently, there are no recommendations regarding mechanical thrombectomy in children despite overwhelming evidence of improved outcomes in adults. Therefore, the need for individual case reports and case series is important to highlight potential advantages and disadvantages in this approach.

Case descriptions

We retrospectively searched our prospectively maintained database of patients undergoing mechanical thrombectomy for ischaemic stroke. We describe five children, aged between 7 and 17, who underwent mechanical thrombectomy for acute ischaemic stroke. We provide an account of their clinical presentations, operative treatment and postoperative outcome.

Discussion

Mechanical thrombectomy in children, especially older children, can be performed safely and with existing devices. Although a randomised controlled trial would provide compelling evidence of the potential advantages to this technique, the lack of this should not prevent the use of this procedure by trained neurointerventionists.

Effects of body size and gender on the population pharmacokinetics of artesunate and its active metabolite dihydroartemisinin in pediatric malaria patients

Despite the important role of the antimalarial artesunate and its active metabolite dihydroartemisinin (DHA) in malaria treatment efforts, there are limited data on the pharmacokinetics of these agents in pediatric patients. This study evaluated the effects of body size and gender on the pharmacokinetics of artesunate-DHA using data from pediatric and adult malaria patients. Nonlinear mixed-effects modeling was used to obtain a base model consisting of first-order artesunate absorption and one-compartment models for artesunate and for DHA. Various methods of incorporating effects of body size descriptors on clearance and volume parameters were tested. An allometric scaling model for weight and a linear body surface area (BSA) model were deemed optimal. The apparent clearance and volume of distribution of DHA obtained with the allometric scaling model, normalized to a 38-kg patient, were 63.5 liters/h and 65.1 liters, respectively. Estimates for the linear BSA model were similar. The 95% confidence intervals for the estimated gender effects on clearance and volume parameters for artesunate fell outside the predefined no-relevant-clinical-effect interval of 0.75 to 1.25. However, the effect of gender on apparent DHA clearance was almost entirely contained within this interval, suggesting a lack of an influence of gender on this parameter. Overall, the pharmacokinetics of artesunate and DHA following oral artesunate administration can be described for pediatric patients using either an allometric scaling or linear BSA model. Both models predict that, for a given artesunate dose in mg/kg of body weight, younger children are expected to have lower DHA exposure than older children or adults.

RNA-Seq reveals different mRNA abundance of transporters and their alternative transcript isoforms during liver development

During development, the maturation of liver transporters is essential for chemical elimination in newborns and children. One cannot compare the real abundance of transcripts by conventional messenger RNA (mRNA) profiling methods; in comparison, RNA-Seq provides a "true quantification" of transcript counts and an unbiased detection of novel transcripts. The purpose of this study was to compare the mRNA abundance of liver transporters and seek their novel transcripts during liver development. Livers from male C57BL/6J mice were collected at 12 ages from prenatal to adulthood. The transcriptome was determined by RNA-Seq, with transcript abundance estimated by Cufflinks. Among 498 known transporters, the ontogeny of 62 known critical xenobiotic transporters was examined in detail. The cumulative mRNAs of the uptake transporters increased more than the efflux transporters in livers after birth. A heatmap revealed three ontogenic patterns of these transporters, namely perinatal (reaching maximal expression before birth), adolescent (about 20 days), and adult enriched (about 60 days of age). Before birth, equilibrative nucleoside transporter 1 was the transporter with highest expression in liver (29%), followed by breast cancer resistance protein (Bcrp) (26%). Within 1 day after birth, the mRNAs of these two transporters decreased markedly, and Ntcp became the transporter with highest expression (52%). In adult liver, the transporters with highest expression were organic cation transporter 1 and Ntcp (23% and 22%, respectively). Three isoforms of Bcrp with alternate leading exons were identified (E1a, E1b, and E1c), with E1b being the major isoform. In conclusion, this study reveals the mRNA abundance of transporters in liver and demonstrates that the expression of liver transporters is both age and isoform specific.

Population pharmacokinetics and dose simulation of carvedilol in paediatric patients with congestive heart failure

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

* Applying in silico tools such as population pharmacokinetic analysis and simulation will help to find adequate dosing strategies and increase the probability of success for a randomized controlled trial. * Up to now, for carvedilol in paediatric patients with congestive heart failure (CHF) the dose has been linearly extrapolated from adults, but the results with this dosing strategy are ambiguous. * Further trials are necessary to establish carvedilol for paediatric patients with CHF.

WHAT THIS STUDY ADDS

* Carvedilol pharmacokinetics in paediatric patients with CHF depends on the weight and age of the patient. * Therefore, the drug exposure differs substantially between patients of different ages receiving the same dose with respect to body weight. * Simulations revealed that an age-adjusted carvedilol dosing strategy with higher doses for younger patients with respect to body weight is preferable to a uniform one.

AIMS

To investigate the ontogeny of carvedilol pharmacokinetics and to develop an age-appropriate carvedilol dosing strategy for paediatric patients.

METHODS

Data were derived from a prospective, nonplacebo-controlled study of carvedilol for the treatment of paediatric patients with congestive heart failure and analysed using a nonlinear mixed-effects modelling approach (NONMEM, Version V 1.1). The population pharmacokinetic model was further utilized for simulations of different carvedilol dosing strategies.

RESULTS

Four hundred and eighty carvedilol plasma concentrations of 41 patients (0.1-19.3 years; median 3.5) were included in the analysis. A two-compartment model with first-order absorption and absorption lag served as structural model. Weight and age were the most important covariates for carvedilol pharmacokinetics. The weight-adjusted clearance was highest for the younger patients with 2.7 l h(-1) kg(-1) for a 1-year-old patient compared with 0.7 l h(-1) kg(-1) for a 19.3-year-old patient. Dose simulations revealed that the area under the plasma concentration-time curve (AUC) as a measure of drug exposure increased with age despite constant doses with respect to body weight. For infants (28 days to 23 months), children (2-11 years) and adolescents (12-15 years) daily doses of 3, 2 and 1 mg kg(-1), administered in two or three discrete doses, were necessary to reach an exposure comparable to adults receiving 0.7 mg kg(-1) day(-1).

CONCLUSION

The ontogeny of carvedilol pharmacokinetics in paediatric patients depends on age and weight. Dose simulations revealed that younger patients have to be treated with higher doses with respect to body weight to reach the same exposure as adults.

Guidelines on paediatric dosing on the basis of developmental physiology and pharmacokinetic considerations

The approach to paediatric drug dosing needs to be based on the physiological characteristics of the child and the pharmacokinetic parameters of the drug. This review summarises the current knowledge on developmental changes in absorption, distribution, metabolism and excretion and combines this knowledge with in vivo and in vitro pharmacokinetic data that are currently available. In addition, dosage adjustments based on practical problems, such as child-friendly formulations and feeding regimens, disease state, genetic make-up and environmental influences are presented. Modification of a dosage based on absorption, depends on the route of absorption, the physico chemical properties of the drug and the age of the child. For oral drug absorption, a distinction should be made between the very young and children over a few weeks old. In the latter case, it is likely that practical considerations, like appropriate formulations, have much greater relevance to oral drug absorption. The volume of distribution (V(d)) may be altered in children. Hydrophilic drugs with a high V(d) in adults should be normalised to bodyweight in young children (age <2 years), whereas hydrophilic drugs with a low V(d) in adults should be normalised to body surface area (BSA) in these children. For drugs that are metabolised by the liver, the effect of the V(d) becomes apparent in children <2 months of age. In general, only the first dose should be based on the V(d); subsequent doses should be determined by the clearance. Pharmacokinetic studies on renal and liver function clarify that a distinction should be made between maturation and growth of the organs. After the maturation process has finished, the main influences on the clearance of drugs are growth and changes in blood flow of the liver and kidney. Drugs that are primarily metabolised by the liver should be administered with extreme care until the age of 2 months. Modification of dosing should be based on response and on therapeutic drug monitoring. At the age of 2-6 months, a general guideline based on bodyweight may be used. After 6 months of age, BSA is a good marker as a basis for drug dosing. However, even at this age, drugs that are primarily metabolised by cytochrome P450 2D6 and uridine diphosphate glucuronosyltransferase should be normalised to bodyweight. In the first 2 years of life, the renal excretion rate should be determined by markers of renal function, such as serum creatinine and p-aminohippuric acid clearance. A dosage guideline for drugs that are significantly excreted by the kidney should be based on the determination of renal function in first 2 years of life. After maturation, the dose should be normalised to BSA. These guidelines are intended to be used in clinical practice and to form a basis for more research. The integration of these guidelines, and combining them with pharmacodynamic effects, should be considered and could form a basis for further study.

Prediction of drug disposition in infants and children by means of physiologically based pharmacokinetic (PBPK) modelling: theophylline and midazolam as model drugs

AIMS

To create a general physiologically based pharmacokinetic (PBPK) model for drug disposition in infants and children, covering the age range from birth to adulthood, and to evaluate it with theophylline and midazolam as model drugs.

METHODS

Physiological data for neonates, 0.5-, 1-, 2-, 5-, 10- and 15-year-old children, and adults, of both sexes were compiled from the literature. The data comprised body weight and surface area, organ weights, vascular and interstitial spaces, extracellular body water, organ blood flows, cardiac output and glomerular filtration rate. Tissue: plasma partition coefficients were calculated from rat data and unbound fraction (f u) of the drug in human plasma, and age-related changes in unbound intrinsic hepatic clearance were estimated from CYP1A2 and CYP2E1 (theophylline) and CYP3A4 (midazolam) activities in vitro. Volume of distribution (V dss), total and renal clearance (CL and CL R) and elimination half-life (t(1/2)) were estimated by PBPK modelling, as functions of age, and compared with literature data.

RESULTS

The predicted V dss of theophylline was 0.4-0.6 l kg(-1) and showed only a modest change with age. The median prediction error (MPE) compared with literature data was 3.4%. Predicted total CL demonstrated the time-course generally reported in the literature. It was 20 ml h(-1) kg(-1) in the neonate, rising to 73 ml h(-1) kg(-1) at 5 years and then decreasing to 48 ml h(-1) kg(-1) in the adult. Overall, the MPE was - 4.0%. Predicted t(1/2) was 18 h in the neonate, dropping rapidly to 4.6-7.2 h from 6 months onwards, and the MPE was 24%. The predictions for midazolam were also in good agreement with literature data. V dss ranged between 1.0 and 1.7 l kg(-1) and showed only modest change with age. CL was 124 ml h(-1) kg(-1) in the neonate and peaked at 664 ml h(-1) kg(-1) at 5 years before decreasing to 425 ml h(-1) kg(-1) in the adult. Predicted t(1/2) was 6.9 h in the neonate and attained 'adult' values of 2.5-3.5 h from 1 year onwards.

CONCLUSIONS

A general PBPK model for the prediction of drug disposition over the age range neonate to young adult is presented. A reference source of physiological data was compiled and validated as far as possible. Since studies of pharmacokinetics in children present obvious practical and ethical difficulties, one aim of the work was to utilize maximally already available data. Prediction of the disposition of theophylline and midazolam, two model drugs with dissimilar physicochemical and pharmacokinetic characteristics, yielded results that generally tallied with literature data. Future use of the model may demonstrate further its strengths and weaknesses.

Population pharmacokinetics of prednisolone in children with acute lymphoblastic leukemia

PURPOSE

To evaluate the plasma protein binding and pharmacokinetics of prednisolone during therapeutic use in children with acute lymphoblastic leukemia (ALL) using the population approach.

METHODS

A two-compartment pharmacokinetic model was used to describe data from 23 children with ALL (aged 2-15 years). Prednisolone (60 mg/m(2) per day in three divided doses) was administered both orally and intravenously, and samples were obtained on several days during the initial 5 weeks of remission induction therapy. Unbound plasma concentrations ( n=288) were determined by HPLC and ultrafiltration. Nonlinear mixed-effects modeling (WinNonMix version 2.0.1) was used to estimate the pharmacokinetic parameters, to identify significant covariates, and to estimate the protein binding parameters.

RESULTS

Prednisolone showed complete oral bioavailability. The median unbound clearance (32 l/h per m(2)) was lower, and the half-life (3.6 h) longer than previously reported in childhood ALL. Body weight was a significant covariate for the central and peripheral volumes of distribution resulting in interindividual variabilities of 50% and 42%. Including body surface area as a covariate for clearance decreased the interindividual variability to 14%. The estimated areas under the unbound plasma concentration-time curves showed less than twofold variation among patients, and a residual variability of 20% indicated that the pharmacokinetic parameters remained stable during induction therapy. The estimated protein binding parameters were comparable to, but slightly lower than, previously published values and independent of the albumin concentration.

CONCLUSIONS

The study showed complete oral bioavailability, a lower unbound clearance and a longer half-life for prednisolone than previously reported in childhood ALL. Plasma protein binding was independent of the albumin concentration. Due to the small inter- and intraindividual variations in the pharmacokinetic parameters, body surface area-based dosing is sufficient to obtain similar systemic exposure among patients.

A phase II trial of liposomal busulphan as an intravenous myeloablative agent prior to stem cell transplantation: 500 mg/m(2) as a optimal total dose for conditioning

We conducted a phase I/II trial, to evaluate the efficacy and safety of an intravenous liposomal formulation of busulphan (LBu) as a myeloablative agent for stem cell transplantation (SCT). The liposomal busulphan was administered as a 3 h infusion twice daily over 4 consecutive days. Six adults received 1.6-2 mg/kg/dose and 18 children received 1.8-3 mg/kg/dose. Pharmacokinetic parameters were studied after the first and the last dose of busulphan. No significant difference in clearance, AUC, elimination half-lives or distribution volume between the first and the last dose was found in either groups. A significantly (P < 0.005) higher clearance was observed in children after the first and the last dose (3.61 and 3.79 ml/min/kg, respectively) compared to adults (2.40 and 2.33 ml/min/kg, respectively). The elimination half-lives after the first and the last dose were significantly (P < 0.005) shorter in children (2.59 and 2.72 h, respectively) compared to adults (3.35 and 3.61 h, respectively). Clearance correlated significantly with age. However, no significant correlation with age was observed when clearance was adjusted to the body surface area. Two cases of VOD following a total dose of 24 mg/kg were observed. Six patients experienced mucositis. No other organ toxicity was observed. We conclude that intravenous liposomal busulphan pharmacokinetics is age dependent. A dosage schedule based on body surface area should be used especially in young children to reduce the age-dependent difference in kinetics. An intravenous liposomal dose of busulphan of 500 mg/m(2) is suggested to reach a similar systemic exposure and myeloablative effect in both children and adults. Moreover, the novel liposomal form of busulphan showed a favorable toxicity profile and seems safe as a part of the high-dose therapy prior to SCT.

Ontogeny of hepatic and renal systemic clearance pathways in infants: part I

Dramatic developmental changes in the physiological and biochemical processes that govern drug pharmacokinetics and pharmacodynamics occur during the first year of life. These changes may have significant consequences for the way infants respond to and deal with drugs. The ontogenesis of systemic clearance mechanisms is probably the most critical determinant of a pharmacological response in the developing infant. In recent years, advances in molecular techniques and an increased availability of fetal and infant tissues have afforded enhanced insight into the ontogeny of clearance mechanisms. Information from these studies is reviewed to highlight the dynamic and complex nature of developmental changes in clearance mechanisms in infants during the first year of life. Hepatic and renal elimination mechanisms constitute the two principal clearance pathways of the developing infant. Drug metabolising enzyme activity is primarily responsible for the hepatic clearance of many drugs. In general, when compared with adult activity levels normalised to amount of hepatic microsomal protein, hepatic cytochrome P450-mediated metabolism and the phase II reactions of glucuronidation, glutathione conjugation and acetylation are deficient in the neonate, but sulfate conjugation is an efficient pathway at birth. Parturition triggers the dramatic development of drug metabolising enzymes, and each enzyme demonstrates an independent rate and pattern of maturation. Marked interindividual variability is associated with their developmental expression, making the ontogenesis of hepatic metabolism a highly variable process. By the first year of life, most enzymes have matured to adult activity levels. When compared with adult values, renal clearance mechanisms are compromised at birth. Dramatic increases in renal function occur in the ensuing postpartum period, and by 6 months of age glomerular filtration rate normalised to bodyweight has approached adult values. Maturation of renal tubular functions exhibits a more protracted time course of development, resulting in a glomerulotubular imbalance. This imbalance exists until adult renal tubule function values are approached by 1 year of age. The ontogeny of hepatic biliary and renal tubular transport processes and their impact on the elimination of drugs remain largely unknown. The summary of the current understanding of the ontogeny of individual pathways of hepatic and renal elimination presented in this review should serve as a basis for the continued accruement of age-specific information concerning the ontogeny of clearance mechanisms in infants. Such information can only help to improve the pharmacotherapeutic management of paediatric patients.

Quantitative near infrared spectroscopy measurement of cerebral hemodynamics in newborn piglets

Severely premature infants are often at increased risk of cerebral hemorrhage and/or ischemic injury caused by immature autoregulatory control of blood flow to the brain. If blood flow is too high, the infant is at risk of hemorrhage, whereas too little blood flow can result in ischemic injury. The development of a noninvasive, bedside means of measuring cerebral hemodynamics would greatly facilitate both diagnosis and monitoring of afflicted individuals. It is to this end that we have developed a near infrared spectroscopy (NIRS) system that allows for quantitative, bedside measurement of cerebral blood flow (CBF), cerebral blood volume (CBV), and mean transit time (MTT). The technique requires an i.v. injection of the near infrared chromophore indocyanine green. Six newborn piglets, median age of 18 h (range 6-54 h), median weight of 1.75 kg (range 1.5-2.1 kg), were studied. Measurements of CBF, CBV, and MTT were made at normocapnia, hypocapnia, and hypercapnia to test the technique over a range of hemodynamic conditions. The accuracy of our new approach has been determined by direct comparison with measurements made using a previously validated computed tomography technique. Paired t tests showed no significant difference between computed tomography and NIRS measurements of CBF, CBV, and MTT, and mean biases between the two methods were -2.05 mL x min(-1) x 100 g(-1), -0.18 mL x 100 g(-1), and 0.43 s, respectively. The precision of NIRS CBF, CBV, and MTT measurements, as determined by repeated-measures ANOVA, was 9.71%, 13.05%, and 7.57%, respectively.

Use of body surface area (BSA)-based dosages to calculate chemotherapeutic drug dose in dogs: I. Potential problems with current BSA formulae

The dose of most cancer chemotherapeutic drugs administered to dogs is calculated on the basis of estimated body surface area (BSA); however results of some chemotherapy trials have revealed that this dosing method increases toxicosis in small dogs. The current formula used to estimate BSA in dogs may be inaccurate or the assumption that BSA correlates with chemotherapeutic drug exposure may be unfounded. Results presented in this review suggest that canine BSA estimates may be inaccurate because the values for the constant (K) and exponent (a) in the formulae (BSA = K.Wa) are incorrect or because a linear parameter such as body length is lacking from the formulae. Results that suggest the relationship between BSA and the physiologic/pharmacologic factors that influence drug exposure may not be closely correlated are also presented. Studies are warranted to determine whether there are dosing methods that normalize chemotherapeutic drug toxicity in dogs.

Developmental expression of cytochrome P450 enzymes in human liver

Drug-metabolizing cytochrome P450 enzymes, the major phase I enzymes, are active in human liver already at very early stages of intrauterine development, although presumably at fairly low concentrations and in low numbers. During maturation, these enzymes go through various developmental programmes towards adulthood. The major increase both in abundance as well as in number of different enzymes takes place after birth, probably during the first year of life. Detailed information concerning these developmental changes is still limited. The major drug-metabolizing P450 enzymes appear to be primarily members of the CYP3A subfamily in all stages of development. The balance between different members of this subfamily, however, undergoes significant switches from the foetal predominant CYP3A7 to the major adult form CYP3A4. The ontogeny of the other cytochrome P450 enzymes is less well characterized, but the major switch-on appears to occur mainly after birth. Developmental expression of P450 enzymes is one of the key factors determining the pharmacokinetic status of developing individuals both pre- and postnatally.

Laser-photosensitizer assisted immunotherapy: a novel modality for cancer treatment

Photosensitizer-enhanced laser treatment, where dyes are activated in situ by lasers of appropriate wavelengths, provides highly selective tissue destruction, both spatially and temporally, through photophysical reactions. Although laser-sensitizer treatment for cancer can achieve a controlled local tumor cell destruction on a large scale, total tumor eradication may not be accomplished because of the incomplete local tumor killing or the presence of tumor metastases, or both. The long-term control of cancer depends on the host immune surveillance and defense systems in which both cell-mediated and humoral responses are critical. In this study we report a novel minimally invasive cancer treatment combining the laser photophysical effects with the photobiological effects. Irradiation of a rat mammary tumor by an 805 nm diode laser, after an intratumor administration of a specific photosensitizer, indocyanine green in a glycated chitosan gel, caused immediate photothermal destruction of neoplastic cells. Concomitantly this treatment stimulated the immunological defense system against residual and metastatic tumor cells. Increases in survival rate and in the eradication of tumor burden, both primary and metastatic, were observed after this treatment. Furthermore, the resistance of successfully treated rats to tumor rechallenge demonstrated a long-lasting systemic effect of the treatment. These findings indicate that our treatment has triggered a specific humoral immune response in the tumor-bearing rats.

Pharmacokinetics of felbamate in pediatric and adult beagle dogs

The relative bioavailability and pharmacokinetics of felbamate (FBM) after a single oral dose and after 10 once-daily oral doses of 60 mg/kg were investigated in adult and pediatric dogs of both sexes. The pediatric and adult dogs were aged 4-6 weeks and 1-2 years, respectively. Analysis of variance (ANOVA) was performed on the bioavailability parameters among all groups and between the first and last doses. No sex-related differences in bioavailability and pharmacokinetic parameters were observed. The bioavailability of FBM in pediatric dogs was significantly less as compared with that in adult dogs. Rapid overall elimination of the drug in pediatric dogs appears to be responsible for the lower bioavailability. The bioavailability of FBM after the last dose was also significantly lower than after the first dose for both age groups. No major differences in the rate constant of FBM absorption (ka) and volume of distribution at steady state (VSS) were observed between the two age groups. As with other clinically useful antiepileptic drugs (AEDs), higher doses of FBM may be required in pediatric populations to achieve optimum drug levels, assuming that age-related changes in FBM disposition will also be confirmed in humans.