The pharmacokinetics and safety of micafungin, a novel echinocandin, in premature infants

BACKGROUND

: Candidal fungal infection rates in neonates are increasing and are a significant cause of mortality, especially in low birth weight infants. Micafungin is an echinocandin that works by inhibiting 1,3-beta-D-glucan synthase, an enzyme responsible for fungal cell wall synthesis. The objective of this study was to determine the safety and pharmacokinetics of micafungin in premature infants.

METHODS

: This was a phase I, single-dose, multicenter, open-label, sequential-dose trial of intravenous micafungin investigating 3 doses (0.75 mg/kg, 1.5 mg/kg and 3.0 mg/kg) in 18 premature infants weighing >1000 g (n = 6 in each dosage group). A further 5 infants (500-1000 g) were enrolled in the 0.75 mg/kg dosage group only.

RESULTS

: The mean +/- standard deviation gestational age in the >1000 g dosage group was 26.4 +/- 2.4 weeks and, on entry, patients had one or more of a variety of underlying conditions, including sepsis, pneumonia and other infections caused by Candida or other species. Micafungin pharmacokinetics in preterm infants appears linear. However, premature infants >1000 g on average displayed a shorter half-life (8 hours) and a more rapid rate of clearance (approximately 39 mL/h per kg) compared with published data in older children and adults. All doses of micafungin were well tolerated and no serious drug-related adverse events were observed.

CONCLUSIONS

: Single doses of micafungin, ranging up to 3.0 mg/kg, appear well tolerated in premature infants weighing >1000 g. The drug's elimination half-life and total plasma clearance in preterm infants appear dissimilar to published values for these parameters in older children and adults. The reason(s) for this apparent difference remain to be investigated.

Effectiveness, safety, and pharmacokinetics of quetiapine in aggressive children with conduct disorder

OBJECTIVE

To provide an initial description of the effectiveness and pharmacokinetics (PK) of quetiapine in aggressive children with conduct disorder (CD).

METHOD

This 8-week, open-label outpatient trial, enrolled patients ages 6 to 12 years with CD. Outcome measures included the Rating of Aggression Against People and/or Property Scale (RAAPPS), Nisonger Child Behavior Rating Form (NCBRF), and the Conners Parent Rating Scale (CPRS-48). Blood sampling for PK analyses occurred at the end of weeks 2 and 8.

RESULTS

Seventeen children (16 boys, mean age 8.9 years) were treated. The mean dose at week 8 was 4.4 mg/kg (SD = 1.1 mg/kg). Significant decreases in the baseline scores of the RAAPPS, and several subscales of the NCBRF and the CPRS were found by the end of the study (p <.05). No patients discontinued because of an adverse event. No patients experienced extrapyramidal side effects. Quetiapine disposition was linear over the dose range studied. The elimination half-life of the drug averaged 3.9 and 2.9 hours and total body clearance averaged 3.5 and 3.0 L/hr/kg after study weeks 2 and 8, respectively.

CONCLUSIONS

These preliminary data suggest that aggressive children with CD may benefit from quetiapine. The PK of quetiapine supports twice-daily dosing in children with CD.

Transfer of the hematopoietic stem cell transplant patient to the intensive care unit: does it really matter?

We critically reviewed published English language literature and concluded that from 1998 onward the survival of hematopoietic stem cell transplant (SCT) patients who experienced intensive care unit (ICU) transfer has improved. The factors associated with increased mortality during ICU stay included increased patient age, allogeneic transplant, intubation/mechanical ventilation, multiorgan system failure (MOSF), presumed/documented infection, graft-versus-host disease, and higher APACHE and O-PRISM score at ICU transfer. This encouraging outcome trend reflects evolving advances such as use of recombinant hematopoietic growth factors, use of mobilized blood cells rather than marrow, protective strategies for acute lung injury and early goal-directed therapy for sepsis syndrome. Patient selection bias (which patients were transferred and which were not sent to an ICU) also plays a role in ICU survival rates. New strategies to improve upon SCT patient outcome include use of a scoring system to predict mortality, better therapies for MOSF and integration of ICU components and multispecialist involvement earlier in the clinical course to prevent severe complications such as respiratory failure. SCT recipients comprise a heterogeneous group; to further advance this field, prospective multicenter trials involving larger populations from many centers are needed to reduce the biases of retrospective and single-center reports.

Health effects of subchronic exposure to diesel-water emulsion emission

The U.S. Environmental Protection Agency (EPA) National Ambient Air Quality Standards for ozone and particulate matter are requiring urban nonattainment areas to implement pollution-reduction strategies for anthropogenic source emissions. A type of fuel shown to decrease combustion emissions components versus traditional diesel fuels is the diesel-water emulsion. The Lubrizol Corporation in conjunction with Lovelace Respiratory Research Institute and several subcontracting laboratories recently conducted a rodent health assessment of inhaled combustion emissions of PuriNO(x) diesel fuel emulsion. Combustion emissions from either of two 2001 model Cummins 5.9-L ISB engines were diluted with charcoal-filtered air to exposure concentrations of 100, 200, and 400 microg total particulate matter/m(3). The engines were operated on a continuously repeating, heavy-duty certification cycle (U.S. Code of Federal Regulations, Title 40, Chapter I) using Rotella-T 15W-40 engine oil. Nitrogen oxide and particulate matter were reduced when engines were operated on PuriNO(x) versus California Air Resources Board diesel fuel under these conditions. Male and female F344 rats were housed in Hazleton H2000 exposure chambers and exposed to exhaust atmospheres 6 h/day, 5 days/wk for the first 11 wk and 7 days/wk threafter. Exposures ranged from 58 to 70 days, depending on the treatment group. Indicators of general toxicity (body weight, organ weight, clinical pathology, and histopathology), neurotoxicity (glial fibrillary acidic protein assay), genotoxicity (Ames assay, micronucleus, sister chromatid exchange), and reproduction and development were measured. Overall, effects observed were mild. Emulsion combustion emissions were not associated with neurotoxicity, reproductive/developmental toxicity, or in vivo genotoxicity. Small decreases in serum cholesterol and small increases in platelet values in some groups of exposed animals were observed. Particulate matter accumulation within alveolar macrophages was evident in all exposure groups. These findings are consistent with normal physiological responses to particle inhalation. Other statistically significant effects were present in some measured parameters of other exposed groups but were not clearly attributed to emissions exposure. Positive mutagenic responses in several strains of Salmonella typhimurium were observed subsequent to treatment with emulsion emissions subfractions. Based on the cholesterol and platelet results, it can be concluded that the 100 microg/m(3) exposure level was the no-observed-effect level. In general, biological findings in diesel emulsion emission-exposed animals and bacteria were consistent with exposure to petroleum diesel exhaust in the F344 rat and Ames assays.

Combination lithium and divalproex sodium in pediatric bipolar symptom re-stabilization

OBJECTIVE

It has been reported that bipolar disorder may become less responsive to previously effective treatment with each symptomatic relapse. The primary goal of this study was to assess the rate of re-stabilization after the resumption of lithium (Li) plus divalproex (DVPX) following relapse on either agent as monotherapy.

METHOD

This is a prospective, 8-week, open-label outpatient Li/DVPX combination therapy trial. Patients ages 5 to 17 years with bipolar disorder type I or II, who had achieved symptom remission with Li/DVPX combination therapy and subsequently relapsed during treatment with Li or DVPX monotherapy were enrolled between January 1999 and January 2003.

RESULTS

Thirty-eight patients with a mean age of 10.5 years entered the study. Thirty-four (89.5%) patients responded to treatment with Li/DVPX mood stabilizer therapy alone, but four patients required adjunctive antipsychotic treatment to address residual symptomatology. Overall, reinitiation of Li/DVPX combination therapy was well tolerated with no subjects discontinuing because of a medication-related adverse event.

CONCLUSIONS

It appears that most youths with bipolar disorder who stabilize on combination Li/DVPX therapy and subsequently relapse during monotherapy can safely and effectively be re-stabilized with the reinitiation of Li/DVPX combination treatment.

Cytokines and toxicity in acetaminophen overdose

Several cytokines have been reported to have hepatoprotective properties in animal models of acetaminophen toxicity. To investigate the relationships of cytokines and toxicity in acetaminophen overdose, blood samples were collected from patients following acute ingestions of acetaminophen. Samples for cytokine analysis were collected at the time of routine clinical monitoring in 111 patients (90 females; mean age 13.6 years). Plasma concentrations of interleukin 6, interleukin 8, interleukin 10, and monocyte chemoattractant protein 1 were analyzed by enzyme-linked immunosorbent assay. Patients were stratified by toxicity severity, defined by the maximal values of hepatic transaminase elevation. Levels of interleukin 6, interleukin 8, and monocyte chemoattractant protein 1 were higher in patients with serum alanine aminotransferase > 1000 IU/L, and monocyte chemoattractant protein 1 had the strongest association with toxicity. Monocyte chemoattractant protein 1 values were higher in patients with greater delays in N-acetylcysteine treatment and in patients with higher values of prothrombin time. Monocyte chemoattractant protein 1 elevation in acetaminophen overdose may represent an innate, immunomodulary response of the liver to earlier events in the toxicity. An understanding of the role of cytokine responses in acetaminophen overdose may be relevant to the future development of new therapies for acetaminophen toxicity.

Improving drug use for children in the developing world

Children differ significantly from adults in the way they absorb, metabolise, and excrete drugs. These parameters also vary as children grow from neonates through to adolescence. The practical implications and challenges that this presents are well know to anyone who is involved in the medical management of sick children. The importance of paediatric medication safety and efficacy has been gaining increasing attention in the developed world over the past decade. The United States has introduced a carrot and stick approach to increase research into medications for children with the "paediatric exclusivity provision" and the "paediatric rule". The European Union is also investigating ways of improving the availability of medications for children. Unfortunately, this increased focus on appropriate medicines for children, which has occurred in the developed world, has not been mirrored in developing nations. Currently more than 10 million children under the age of 5 years die each year, with only six countries accounting for 50% of these deaths. The majority of these deaths are from treatable or preventable diseases. The developed world has a moral and ethical obligation to share its gains with the children of the world.

Explaining the poor bacteriologic eradication rate of single-dose ceftriaxone in group a streptococcal tonsillopharyngitis: a reverse engineering solution using pharmacodynamic modeling

OBJECTIVE

To explore pharmacokinetic factors underlying the poor bacteriologic eradication rate with a single 500-mg dose of ceftriaxone for streptococcal tonsillopharyngitis and to identify the minimum ceftriaxone dose required for effective treatment.

METHODS

Population modeling techniques were applied to pharmacokinetic data derived from paired plasma and tonsil samples from 153 children to assess the contribution of pharmacokinetic variability to patients' responses to ceftriaxone. In addition, a Monte Carlo simulation was performed to determine (1) the amount of time that free ceftriaxone concentrations must exceed the minimum inhibitory concentration (MIC) of group A Streptococcus to achieve bacteriologic eradication and (2) the ceftriaxone dose required to maintain free drug concentrations above the target MIC for the requisite amount of time. Ceftriaxone MICs for group A Streptococcus were obtained from a previous trial, in which all MICs (n = 115) were < or = 0.064 mg/L; 33.9% were susceptible at < or = 0.016 mg/L, 66.4% were susceptible at 0.032 mg/L, and 1.7% were susceptible at 0.064 mg/L.

RESULTS

Mean population pharmacokinetic parameters and their variances reflected substantial variability of clearance and half-life in the target population. Tonsillar ceftriaxone protein binding was 89.1%. The proportions of 1000 simulated patients with free ceftriaxone concentrations that exceeded MICs of 0.016 mg/L, 0.032 mg/L, and 0.064 mg/L at 24 hours were 71.7%, 65.4%, and 57.2%, respectively, and at 48 hours were 41.8%, 35.8%, and 28.6%, respectively. The amount of time that free ceftriaxone concentrations need to exceed MIC to achieve bacteriologic success was estimated to be 36 hours. Using this time criterion, two 500-mg doses of ceftriaxone separated by 18 hours should achieve a bacteriologic cure rate of approximately 95%.

CONCLUSIONS

Pharmacokinetic variability and high ceftriaxone tonsillar protein binding explain the high microbiologic failure rate for a single 500-mg dose of ceftriaxone in group A streptococcal tonsillopharyngitis. Monte Carlo simulation suggests that a second dose administered 18 hours after the first will be required to achieve an acceptable bacteriologic cure rate.

Pharmacokinetics of gatifloxacin in infants and children

Gatifloxacin is an 8-methoxy fluoroquinolone effective against a broad spectrum of pathogens common in pediatric infections. The safety and pharmacokinetics of a single dose of gatifloxacin were studied in pediatric patients from 6 months to 16 years of age. Seventy-six pediatric patients (average age, 6.7 +/- 5.0 years) were administered a single oral dose of gatifloxacin suspension (5, 10, or 15 mg/kg of body weight; 600-mg maximum) in a dose-escalating manner. Subjects were stratified by age into 4 groups. An additional 12 children, greater than 6 years of age, received gatifloxacin as the tablet formulation at a dose of approximately 10 mg/kg. Gatifloxacin's apparent clearance and half-life were 5.5 +/- 2.1 ml/min/kg and 5.1 +/- 1.4 h. The maximum concentration of drug in plasma and area under the concentration-time curve (AUC) increased in a manner approximately proportional to the dose. At the 10-mg/kg dose, the bioavailability was similar between the suspension and tablet formulation. The apparent oral clearance of gatifloxacin, normalized for body weight, exhibited a small but statistically significant decrease with increasing age. In all subjects receiving gatifloxacin at 10 mg/kg, the AUC exceeded 20 microg . h/ml (estimated free AUC/MIC ratio of > or =34 for MIC of < or =0.5 microg/ml). These data suggest that gatifloxacin at a dose of 10 mg/kg every 24 h will achieve therapeutic concentrations in plasma in infants and children.

Double-blind 18-month trial of lithium versus divalproex maintenance treatment in pediatric bipolar disorder

OBJECTIVE

To determine whether divalproex sodium (DVPX) was superior to lithium carbonate (Li+) in the maintenance monotherapy treatment of youths diagnosed with bipolar disorder who had been previously stabilized on combination Li+ and DVPX (Li+/DVPX) pharmacotherapy.

METHOD

Youths ages 5-17 years with bipolar I or II disorder were initially treated with Li /DVPX. Patients meeting remission criteria for four consecutive weeks were then randomized in a double-blind fashion to treatment with either Li+ or DVPX for up to 76 weeks. Study participation ended if the subject required additional clinical intervention or if the subject did not adhere to study procedures.

RESULTS

Patients were recruited between July 1998 and May 2002. One hundred thirty-nine youths with a mean (SD) age of 10.8 (3.5) years were initially treated with Li+/DVPX for a mean (SD) duration of 10.7 (5.4) weeks. Sixty youths were then randomized to receive monotherapy with Li+ (n = 30) or DVPX (n = 30). The Li+ and DVPX treatment groups did not differ in survival time until emerging symptoms of relapse (p = .55) or survival time until discontinuation for any reason (p = .72).

CONCLUSIONS

DVPX was not found to be superior to Li+ as maintenance treatment in youths who stabilized on combination Li+/DVPX pharmacotherapy.

Intra-atrial tissue plasminogen activator infusion for prosthetic valve thrombosis

Thrombosis is a well-known and life-threatening complication of prosthetic mechanical valves. Therapy typically requires medical thrombolysis or surgical thrombectomy/valve replacement. We report the case of a thrombosed atrioventricular valve in a young boy with complex congenital heart disease, which was successfully treated with direct intra-atrial infusion of recombinant tissue plasminogen activator after failed attempts at systemic therapy. We present this treatment as an alternative to conventional medical therapy.

Perinatal toxicity of domestic naphthalene exposure

Naphthalene-containing mothballs can cause methemoglobinemia on inhalation. We describe a mother with hemolytic anemia and methemoglobinemia associated with elevated levels of naphthalene following exposure to mothballs. Her newborn infant had identical symptoms requiring mechanical ventilation and an exchange transfusion for resolution.

Quetiapine in nine youths with autistic disorder

OBJECTIVE

The aim of this study was to examine the effectiveness of quetiapine in adolescents suffering from autistic disorder (AD).

METHODS

This was a 12-week, open-label study, for which medically healthy patients with AD between the ages of 10 and 17 years were eligible. Quetiapine treatment was gradually increased over the first 6 weeks of the study, to a total daily dose of 300 mg/day. Doses could then be increased to a maximum daily dose of 750 mg/day. Outcome measures included the Children's Psychiatric Rating Scale (CPRS) and the Clinical Global Impressions (CGI) scale.

RESULTS

Nine (9) males were enrolled. Six (6) patients had previously been treated with other psychotropic agents. Although improvements in several symptom domains were observed on quetiapine, only 2 patients met a priori criteria for response ("much" or "very much improved" on the Clinical Global Impressions-Improvement Scale). In addition, only these same 2 patients' parents/guardians chose to continue quetiapine pharmacotherapy after study participation.

CONCLUSIONS

These data suggest that quetiapine may not be a particularly effective agent in the treatment of adolescent patients with AD. However, should future studies be performed, it seems reasonable that they be conducted with more rigor, less treatment-resistant cohorts, and, possibly, a different dosing strategy.

Retrospective study of the renal effects of amphotericin B lipid complex when used at higher-than-recommended dosages and longer durations compared with lower dosages and shorter durations in patients with systemic fungal infections

BACKGROUND

Patients with fungal infections who are treated with amphotericin B lipid complex (ABLC) often receive dosages less than that recommended in the product information (5 mg/kg.d). This occurs despite the described safety and increased efficacy in select patients treated with higher ABLC dosages.

OBJECTIVE

The purpose of this study was to compare the renal effects of high-dosage/long-duration (HDos/LDur) ABLC therapy (>5 mg/kg.d for >12 days) with those of low-dosage/short-duration (LDos/SDur) ABLC therapy (<or=5 mg/kg.d for <or=12 days).

METHODS

Male and female ABLC-treated patients of all ages were prospectively enrolled, and data were retrospectively collected for those who had received >or=4 ABLC doses according to a large, multicenter patient database, the Collaborative Exchange of Antifungal Research (CLEAR) registry. The safety profile of each dosage was evaluated using serum creatinine concentration (S-Cr) and calculated creatinine clearance (CCcr).

RESULTS

A total of 1726 patients were studied. The HDos/LDur group included 309 patients and theLDos/SDur group included 1417 patients. The median ages of the HDos/LDur and LDos/SDur groups were 42 and 48 years, respectively (ranges, <1 to 83 and <1 to 95 years; P < 0.001); females comprised 51% and 42% of the 2 populations (P = 0.004); and 6% and 12% had solid tumors (P = 0.002). The HDos/LDur group was more likely than the LDos/SDur group to have been treated for multiple systemic fungal pathogen infections (16% and 9%, respectively) and for mold infections (28% and 12%, respectively) (both, P < 0.001). The median change in S-Cr from baseline was 0.1 mg/dL in both groups (range, -4.9 to 5 mg/dL in the HDos/LDur group and -3.96 to 4.7 mg/dL in the LDos/SDur group). No increased risk for renal dysfunction, as reflected in the median change from baseline in CCcr, was observed in either cohort (-3 mL/min [range, -118.65 to 69.03 mL/min] in the HDos/LDur group; -2.17 mL/min [range, -107.48 to 104.45 mL/min] in the LDos/SDur group).

CONCLUSION

These data suggest that higher ABLC dosages appear to be as well tolerated as lower dosages, warranting further study of ABLC dosages >5 mg/kg.d for >12 days in the treatment of systemic fungal infections.

Dose modification protocol using intravenous busulfan (Busulfex) and cyclophosphamide followed by autologous or allogeneic peripheral blood stem cell transplantation in patients with hematologic malignancies

We evaluated the safety and toxicity through a 5-cohort dose-modification model of once-daily administration of IV busulfan (Bu) in combination with high-dose cyclophosphamide (Cy) as preparative therapy for stem cell transplantation. Twenty-one adult patients with hematologic malignancies were evaluated. Eleven patients underwent autologous and 10 patients underwent HLA-matched sibling allogeneic transplantation. Patients were sequentially enrolled into 5 cohorts. Cohort 1 received intravenous (IV) Bu 1.6 mg/kg every 12 hours for 2 doses and then 0.8 mg/kg every 6 hours for 12 doses; cohort 2 received IV Bu 1.6 mg/kg every 12 hours for 4 doses and then 0.8 mg/kg every 6 hours for 8 doses; cohort 3 received IV Bu 3.2 mg/kg for 1 dose and then 1.6 mg/kg every 12 hours for 2 doses and 0.8 mg/kg every 6 hours for 8 doses; cohort 4 received IV Bu 3.2 mg/kg every 24 hours for 2 doses and then 0.8 mg/kg every 6 hours for 8 doses; and cohort 5 received IV Bu 3.2 mg/kg every 24 hours for 4 doses. In all groups, Bu was administered on day -7 through day -4 and was followed at least 6 hours after the last Bu dose by Cy 60 mg/kg daily for 2 doses on days -3 and -2. Blood samples were collected for pharmacokinetic analysis on the first and last day of IV Bu administration. All patients were alive and had engrafted at day 30. Five patients developed grade 3 or 4 toxicities. Four patients developed hepatic abnormalities, and 3 exhibited evidence of veno-occlusive disease. Two of 3 patients in cohort 5 with a Bu area under the curve >6000 micromol/min developed autopsy-confirmed veno-occlusive disease. Interpatient variability in AUCs was observed in patients within and between cohorts, but no statistically significant interpatient differences were observed in Bu half-life, volume of distribution, clearance, or dose-adjusted area under the curve. Further, minimal variability in Bu pharmacokinetics was observed between the 2 evaluations performed in each patient, thus reflecting the stability of Bu disposition within individual patients. On the basis of the dosing guidelines and schedule outlined in this study, our data suggest that administration of IV Bu 3.2 mg/kg IV every 24 hours for 4 doses in combination with Cy may result in excessive toxicity.

Intentional Topiramate Ingestion in an Adolescent Female

OBJECTIVE:

To describe an intentional topiramate ingestion by an adolescent and warn of the potential for topiramate abuse.

CASE SUMMARY:

A 17-year-old female intentionally ingested approximately eight 100-mg topiramate tablets for the purpose of “getting high.” Soon after ingestion, she was found at school obtunded and nonresponsive. Upon transfer to the emergency department, she became combative and aggressive with evolving neurologic abnormalities including incoherence, confusion, disorientation, and significant speech impairments including echolalia. Approximately 24 hours after ingestion, the patient had completely recovered without requiring specific treatment or experiencing sequelae.

DISCUSSION:

The clinical effects following acute topiramate intoxication appear consistent with the drug's known pharmacologic properties. There are few other reports of topiramate ingestions and most cases have had mild outcomes.

CONCLUSIONS:

Due to the multifactorial effects topiramate may have upon the central nervous system and its anorectic effect, abuse of this drug by adolescents should be considered upon presentation of an adolescent with mental status changes.

Antifungals in systemic neonatal candidiasis

Fungal infections are common in the newborn period, especially among premature neonates, and are responsible for considerable morbidity and mortality. Currently, three classes of antifungals are commonly used in the treatment of systemic fungal infections in neonates: the polyene macrolides (e.g. amphotericin B [deoxycholate and lipid preparations]); the azoles (e.g. fluconazole); and the fluorinated pyrimidines (e.g. flucytosine). The echinocandins (e.g. caspofungin and micafungin) are a newer class of antifungals which shows promise in this population.The available kinetic data on amphotericin B deoxycholate in neonates are derived from very small studies and exhibit considerable variability. There are no kinetic data available for the use of lipid preparations in this population and, again, much has been inferred from adult studies. The information available for flucytosine is also limited but appears similar to what is observed in adults. Fluconazole has the most neonatal pharmacokinetic data, which show slightly less variability than the other antifungals. Genomic factors which affect the metabolism of amphotericin B and fluconazole may explain some of the observed variability. Most of the data for the efficacy of antifungal drugs in neonates are derived from retrospective studies and case reports. The data for amphotericin B deoxycholate and flucytosine are limited. There are more data for the liposomal and lipid complex preparations of amphotericin B and for fluconazole in this population. These support the use of these drugs in neonates, but because of their largely noncomparative nature they can not define the optimal dosage or duration of therapy. Amphotericin B deoxycholate is primarily nephrotoxic. It also induces electrolyte abnormalities and is to a lesser degree cardiotoxic. This toxicity in neonates appears similar to published data in older children and adults. While the lipid preparations of amphotericin B owe their existence to a presumed decrease in toxicity, the observed toxicity in neonates appears to be equal to that seen with the deoxycholate, although it should be noted that the lipid preparations are usually given at much higher dosages. Fluconazole toxicity appears to be milder and less frequent in this population than is seen with amphotericin B. In the final analysis, we do not have sufficient data to define the pharmacokinetic profiles, optimal dose or duration of therapy, or toxicity for any of these compounds in neonates. Further studies are necessary if the optimisation of antifungal therapy in this population is to continue.

Evaluation of risks associated with short- and long-term psychostimulant therapy for treatment of ADHD in children

Attention-deficit hyperactivity disorder (ADHD) is a common condition during childhood that is associated with significant psychosocial dysfunction. Psychostimulants are the compounds that have been most extensively studied for the treatment of ADHD in children. There is substantial scientific evidence that several methylphenidate- and amphetamine-based preparations have acute efficacy in the treatment of this condition in children. The short-term safety and tolerability of these compounds has been reasonably well-studied and the risks associated with psychostimulant therapy in the short-term are generally acceptable. However, the amount of long-term effectiveness and safety data relating to these compounds is relatively small. Data that do exist suggest that long-term treatment with psychostimulants in appropriately diagnosed patients may be associated with salutary effects as well as relatively modest risks. Until more extensive, methodologically rigorous data are available, it appears that judicious psychostimulant pharmacotherapy of ADHD in children may be justified.

Divalproex-ER pharmacokinetics in older children and adolescents

Valproic acid pharmacokinetic profile and tolerability after administration of divalproex sodium extended-release tablets was characterized in older children and adolescents. In this multiple-dose, open-label, pharmacokinetic study, the patients were divided into two age groups, 8-11 years (older children; n = 15) and 12-17 years (adolescents; n = 14). Once-daily administration of divalproex sodium extended-release tablets (doses ranged from 250 to 1750 mg) in older children and adolescents produced relatively flat plasma valproic acid concentration-time profiles over the entire 24-hour dosing interval, similar to the pharmacokinetic performance of this formulation in adults. The mean (standard deviation) oral clearance values for unbound valproic acid were 94.3 (51.8) and 82.3 (28.2) mL/h/kg and for total valproic acid were 11.2 (3.77) and 9.06 (2.03) mL/h/kg in older children and adolescents, respectively. Two patients discontinued for administrative reasons, whereas one discontinued for an adverse event (flulike syndrome). Adverse events reported by three or more patients were flu syndrome (5 patients, 17.2%) and headache (3 patients, 10.3%). Reported adverse events were generally mild to moderate in severity and similar to those reported in previous divalproex studies. This study demonstrates that in older children and adolescents, once-daily administration of divalproex sodium extended-release tablets may potentially be used to sustain plasma valproic acid concentrations within the usually accepted therapeutic ranges for various indications.

Pharmacokinetic properties and tolerability of single-dose terbutaline in patients with severe asthma treated in the pediatric intensive care unit

BACKGROUND

Asthmatic children requiring treatment in the pediatric intensive care unit (PICU) receive aggressive drug therapy that may include IV administration of β 2-receptor agonists to prevent progression to life-threatening respiratory failure. The only pharmacologic agent in this class currently available for parenteral use in the United States is terbutaline. Study of IV dosing of terbutaline in the pediatric population has been limited.

OBJECTIVE

The aim of this study was to determine the pharmacokinetic (PK) properties and tolerability of single-dose terbutaline in pediatric patients across a broad age range who were admitted to the PICU and were receiving maximal conventional asthma drug therapy.

METHODS

This study was conducted at the PICU at Rainbow Babies and Children's Hospital (Cleveland, Ohio). Patients aged 6 months to 16 years with severe exacerbation of reactive airways disease and who were undergoing maximal conventional therapy and had an arterial catheter were enrolled. Patients were arbitrarily assigned to receive a single IV infusion of 1 of 3 doses of terbutaline (10, 20, or 30 μg/kg), infused over 5 minutes. Blood samples were obtained for the determination of plasma terbutaline concentrations just before terbutaline was administered (baseline), immediately on completion of the IV infusion, and at 10, 20, and 40 minutes and 1, 2, 4, 8, 16, 32, 48, and 72 hours after the 5-minute infusion. PK properties (elimination half-life [tl2], mean residence time [MRT], apparent steady-state volume of distribution [Vdss], and total body clearance [CI]) were determined and adverse effects were recorded.

RESULTS

The determination of terbutaline PK properties was possible in 50 of 56 enrolled patients (31 boys, 19 girls; mean [SD] age, 6.5 [4.5] years). The PK properties of terbutaline were linear over the dose range studied and, with the exception of the expected dose-dependent increases in peak terbutaline plasma concentration and area under the terbutaline plasma concentration-time curve, no statistically significant differences were observed in PK relative to dose. Therefore, we pooled the data for all subsequent analyses. Statistically significant correlations with patient age were observed with tl2 (r = 0.4, P < 0.006), MRT (r = 0.4, P < 0.002), and Vdss (r = 0.33, P < 0.02), but not C1 (r = -0.03, P = NS). Single-dose terbutaline administration was generally well tolerated.

CONCLUSIONS

Single-dose IV terbutaline was well tolerated in this study. In maximally treated asthmatic patients in the PICU, terbutaline elimination may be more rapid than in nonacutely ill children. These PK data suggest that if the drug is to be administered intravenously, the continuous IV infusion method, including loading doses for any subsequent dose escalations, may be the most appropriate. The influence of age and safety of long-term, continuous terbutaline IV infusion requires further study.

Acetaminophen intoxication and length of treatment: how long is long enough?

The currently recommended dosing scheme for treating acetaminophen overdose in the United States consists of a loading dose of oral N-acetylcysteine 140 mg/kg, followed by 70 mg/kg every 4 hours for 17 doses, for a total of 72 hours of oral N-acetylcysteine therapy. This protocol has been both effective and safe. We critically evaluated the evidence that supports reducing the course of N-acetylcysteine therapy from 72 hours to 24 or 36 hours. This shorter regimen offers important benefits for both the patient and the patient's family, such as increased drug tolerability and reduced hospital stay. Patients who intentionally ingested acetaminophen with harmful intent could receive appropriate psychosocial treatment more quickly. In addition, shorter courses of N-acetylcysteine therapy have positive financial ramifications by reducing the hospital stay by 1 or 2 days. Clearly, a shorter treatment regimen would not be appropriate for all patients, particularly those who seek treatment late (> 24 hrs after ingestion) and those with evidence of organ toxicity. In order to provide the necessary evidence to support a change in accepted clinical practice, further investigation on the safety and efficacy of a shorter N-acetylcysteine regimen should be conducted by clinical researchers in a controlled manner.

Combination lithium and divalproex sodium in pediatric bipolarity

OBJECTIVE

Lithium carbonate (Li) or divalproex sodium (DVPX) may be effective for some juveniles with bipolar disorder. Many youths with bipolar disorder do not respond to DVPX or Li monotherapy. An open-label study was conducted to examine the effectiveness of combination DVPX and Li therapy with youths diagnosed with bipolar disorder.

METHOD

Patients meeting DSM-IV criteria for bipolar I or bipolar II disorder, ages 5 to 17 years, were treated prospectively for up to 20 weeks with DVPX + Li. Assessments included the Young Mania Rating Scale (YMRS), Children's Depression Rating Scale-Revised (CDRS-R), and the Children's Global Assessment Scale (CGAS). The a priori definition of clinical remission utilized included four contiguous weekly ratings of YMRS </=12.5, CDRS-R </=40, CGAS >/=51, clinical stability, and no evidence of mood cycling.

RESULTS

Ninety patients (66 males, 24 females) were treated. Significant improvement (p <.0001) in all outcome measures was observed by week 8 as well as at the end of study. The mean time in study was 11.3 weeks. Forty-seven percent (n = 42) met a priori criteria for remission.

CONCLUSIONS

Symptoms of mania and depression in juvenile bipolar disorder may be safely and effectively treated acutely with DVPX + Li.

An open-label pilot study of St. John's wort in juvenile depression

OBJECTIVE

This pilot study examined the effectiveness, safety, tolerability, and pharmacodynamics of Hypericum perforatum (St. John's wort) in the treatment of youths diagnosed with major depressive disorder.

METHOD

Youths 6 to 16 years of age meeting DSM-IV criteria for major depressive disorder with depressive symptoms of at least moderate severity were eligible to enroll between January 1999 and January 2001 in this 8-week, prospective, open-label, outpatient study. Outcome measures included the Children's Depression Rating Scale-Revised (CDRS-R) and the Clinical Global Impressions (CGI) scale. A priori criteria for response consisted of a CDRS-R score of </=28 and a CGI severity score </=2. Patients were initially prescribed 150 mg St. John's wort three times daily. If at the end of week 4 the patient did not meet a priori response criteria, the dose was increased to 300 mg three times daily.

RESULTS

Thirty-three youths with a mean (SD) age of 10.5 (2.9) years were enrolled. After 4 weeks of St. John's wort therapy, 22 youths had their dose increased to 900 mg/day. Twenty-five of the patients met response criteria after 8 weeks of treatment. Overall, St. John's wort was well tolerated.

CONCLUSION

St. John's wort may be an effective treatment for youths diagnosed with major depressive disorder. Placebo controlled trials seem indicated.

Antibiotics and breast-feeding: a critical review of the literature

Continuous breast-feeding, an integral component of the postpartum period, is often threatened upon maternal initiation of antibiotics. The real risk of antibiotic use while breast-feeding must be carefully analysed with regard to all the variables that influence the extent of antibiotic distribution into breast milk, including breast milk composition, physicochemical properties of the antibiotic (molecular weight, lipid solubility, pH, protein binding), length of feeding, and maternal disposition. In addition, infant disposition, including ability to absorb, metabolize, eliminate, and tolerate any amounts of antibiotic, must also be considered prior to maternal administration of antibiotic. The milk to plasma (M/P) ratio is a frequently quoted parameter used to predict drug distribution into breast milk. However, its utility is questionable and often fraught with misinterpretation. An alternative approach when the amount of antibiotic concentration in breast milk is known (through clinical trials) is to calculate an estimated or expected infant drug exposure factoring in known/expected milk consumption, drug concentration and bioavailability. In this review, the following antibiotic classes and current literature regarding their distribution into breast milk are critically reviewed: beta-lactam antibiotics, fluoroquinolones, sulfonamides, macrolides, aminoglycosides, tetracyclines, nitrofurantoin, metronidazole, vancomycin, clindamycin and chloramphenicol. In the majority of instances, these antibiotics do not distribute into breast milk in sufficient concentrations to be of any clinical consequence in the breast-feeding infant.

Synergistic activity of colistin and ceftazidime against multiantibiotic-resistant Pseudomonas aeruginosa in an in vitro pharmacodynamic model

Despite the marketing of a series of new antibiotics for antibiotic-resistant gram-positive bacteria, no new agents for multiple-antibiotic-resistant gram-negative infections will be available for quite some time. Clinicians will need to find more effective ways to utilize available agents. Colistin is an older but novel antibiotic that fell into disfavor with clinicians some time ago yet still retains a very favorable antibacterial spectrum, especially for Pseudomonas and Acinetobacter spp. Time-kill curves for two strains of multiantibiotic-resistant Pseudomonas aeruginosa were generated after exposure to colistin alone or in combination with ceftazidime or ciprofloxacin in an in vitro pharmacodynamic model. MICs of colistin, ceftazidime, ciprofloxacin, piperacillin-tazobactam, imipenem, and tobramycin were 0.125, > or =32, >4, >128/4, 16, and >16 mg/liter, respectively. Colistin showed rapid, apparently concentration-dependent bactericidal activity at concentrations between 3 and 200 mg/liter. We were unable to detect increased colistin activity at concentrations above 18 mg/liter due to extremely rapid killing. The combination of colistin and ceftazidime was synergistic (defined as at least a 2-log(10) drop in CFU per milliliter from the count obtained with the more active agent) at 24 h. Adding ciprofloxacin to colistin did not enhance antibiotic activity. These data suggest that the antibacterial effect of colistin combined with ceftazidime can be maximized at a peak concentration of < or =18 mg/liter.

Ciprofloxacin plus piperacillin compared with tobramycin plus piperacillin as empirical therapy in febrile neutropenic patients. A randomized, double-blind trial

BACKGROUND

Therapy with an aminoglycoside and a beta-lactam remains common empirical therapy for febrile neutropenic patients. Concerns of aminoglycoside-induced ototoxicity and nephrotoxicity have led to studies of alternate regimens.

OBJECTIVE

To determine whether ciprofloxacin-piperacillin is equivalent to tobramycin-piperacillin as empirical therapy for neutropenic fever.

DESIGN

Randomized, double-blind multicenter trial.

SETTING

Seven U.S. university-affiliated hospitals and one private research center.

PATIENTS

Febrile (temperature >/= 38 degrees C), neutropenic (neutrophil level < 1 x 10(9) cells/L) hospitalized patients who had leukemia, lymphoma, or solid tumors, or were undergoing bone marrow transplantation.

INTERVENTIONS

Patients received piperacillin, 50 mg/kg of body weight intravenously every 4 hours, and ciprofloxacin, 400 mg intravenously every 8 hours, or tobramycin, 2 mg/kg intravenously every 8 hours.

MEASUREMENTS

Success was defined as resolution of infection and previously positive cultures without the need to give additional antimicrobial agents.

RESULTS

543 febrile episodes were evaluated, of which 471 were clinically evaluable (234 in the ciprofloxacin-piperacillin group and 237 in the tobramycin-piperacillin group). Success rates in the ciprofloxacin-piperacillin group (63 of 234 febrile episodes) and tobramycin-piperacillin group (52 of 237 episodes) were similar (27% vs. 22%, respectively; difference, 5.0 percentage points [95% CI, -2.3 to 12.8 percentage points]), as was survival (96.2% of patients receiving ciprofloxacin-piperacillin versus 94.1% of patients receiving tobramycin-piperacillin; difference, 2.1 percentage points [CI, -2.2 to 6.4 percentage points]). Additions to the initial antimicrobial regimen were the most common reason for treatment failure in both groups (accounting for 67% of failures in the ciprofloxacin-piperacillin group and 72% in the tobramycin-piperacillin group; difference, 5.0 percentage points [CI, -13.8 to 3.7 percentage points]). Fevers resolved faster in patients receiving ciprofloxacin-piperacillin than in patients receiving tobramycin-piperacillin (mean, 5 vs. 6 days) (P = 0.005). No significant differences in adverse events or toxicity were noted (P = 0.083).

CONCLUSION

Ciprofloxacin-piperacillin is as safe and effective as tobramycin-piperacillin for empirical therapy of neutropenic fever.

Clinical pharmacology of bivalirudin

Much progress has been made in understanding and treating acute coronary syndromes. For patients undergoing percutaneous transluminal coronary angioplasty, anticoagulant therapy during the procedure must strike a balance between providing sufficient anticoagulation to prevent thrombus formation and ischemic complications while averting hemorrhagic complications. Bivalirudin, a thrombin-specific anticoagulant, is the only anticoagulant that reduces both ischemic and bleeding complications associated with percutaneous coronary intervention (PCI). Bivalirudin is easy to use, provides predictable anticoagulation, inactivates both free and clot-bound thrombin, and blocks thrombin-mediated platelet activation and aggregation. Drug-drug interaction studies have found no clinically relevant interactions between bivalirudin and ticlopidine, abciximab, tirofiban, or eptifibatide. Bivalirudin is well tolerated by patients who previously received low-molecular-weight heparin (LMWH), when LMWH is discontinued 8-14 hours before bivalirudin is started. Similarly, switching from heparin to bivalirudin at the time of PCI reduces both ischemic and bleeding events.

Pemoline ingestion in children: a report of five cases and review of the literature

The authors describe five pediatric cases of excessive pemoline ingestion. Based on their experience compared with previously reported cases in the literature, they describe the clinical presentation and rational treatment recommendations for acute pemoline ingestion. Overall, patients experienced a relatively benign clinical course following pemoline ingestion. Symptoms of pemoline ingestion appear to be primarily an accentuation of the drug's pharmacological effects on the central nervous and cardiovascular systems with sinus tachycardia, hypertension, hyperactivity, choreoathetoid movements, and hallucinations being most commonly observed. These findings are consistent with previously reported cases. Possible rhabdomyolysis manifested by evaluation of serum CPK was also observed in 3 of 4 patients in whom this laboratory parameter was measured and appears to be a common finding in acute pemoline poisoning. After acute ingestion, symptoms occurred within 6 hours, lasting up to 48 hours in all patients. Gastric lavage and/or activated charcoal would be effective decontamination measures, whereas ipecac-induced emesis should be avoided after massive ingestion due to the possibility of seizures. Aggressive use of a benzodiazepine appears a reasonable first choice to treat associated involuntary movements, tremor, hyperactivity, irritability, and agitation. Phenothiazines or butyrophenones may also be used especially for serious life-threatening symptoms, including hypertensive crisis and severe hyperthermia, although these serious complications of stimulant overdose have not been reported after pemoline ingestion. If a patient should experience pemoline-induced hypertensive crisis, individual dose titration of labetalol or sodium nitroprusside would appear reasonable pharmacologic approaches for rapid stabilization of blood pressure.

The single-dose pharmacokinetics of midazolam and its primary metabolite in pediatric patients after oral and intravenous administration

The first-dose pharmacokinetics of midazolam and its primary alpha-hydroxymetabolite were studied after single-dose administration. Eligible study patients were enrolled into one of three study arms: Arm I (midazolam/metabolite pharmacokinetic evaluation after oral administration of a syrup formulation), Arm II (the absolute bioavailability of midazolam syrup), and Arm III (midazolam and metabolite pharmacokinetics after IV administration). Complete blood sampling for pharmacokinetic analysis was available in 87 subjects. Midazolam absorption after administration of the oral syrupformulation was rapid, with adolescents absorbing the drug at approximately half the rate observed in younger children (ages 2 to < 12 years). Furthermore, midazolam t 1/2 was prolonged and CL/F reducedin adolescents as compared with younger children. Although the midazolam Vd/F appeared larger in the youngest age group after oral administration, this observation was not apparent after IV dosing, suggesting subject differences in bioavailability rather than distribution. Like midazolam, the disposition characteristics for a-hydroxymidazolam were also highly variable, with the greatest formation of metabolite (reflected by the AUC ratio) observed in children ages 2 to < 12 years. The A UC ratios of alpha-hydroxymidazolam to midazolam after IV dosing were similar across all age groups and were smaller than corresponding values following oral administration. The absolute bioavailability of midazolam averaged 36% with a very broad range (9%-71%). No relationship between midazolam bioavailability and age was observed. Overall, the disposition characteristics of midazolam and its a-hydroxy metabolite were highly variable, appeared independent of age and dose administered, and were linear over the dose range studied (0.25 to 1 mg/kg). These data suggest that an initial oral dose of 0.2 to 0.3 mg/kg should be adequateforsuccessful sedation of most pediatric patients. The inherent variability in midazolam bioavailability and metabolism underscores the importance of titrating midazolam dose to desired effect.

The pharmacokinetics of colistin in patients with cystic fibrosis

The safety and pharmacokinetics of colistin were determined after first dose (n = 30) and again under steady-state conditions (n = 27) in 31 patients with cystic fibrosis receiving the drug as a component of their treatment for an acute pulmonary exacerbation of their disease. Patients ranged in age from 14 to 53 years and received colistin for 6 to 35 days. Each patient was started on colistin 5 to 7 mg/kg/day administered intravenously in three equally divided doses. Elimination half-life (t1/2), mean residence time (MRT), steady-state volume of distribution (Vdss), total body clearance (Cl), and renal clearance (Clr) after first-dose administration averaged 3.4 hours, 4.4 hours, 0.09 l/kg, and 0.35 and 0.24 ml/min/kg, respectively. No differences in colistin disposition characteristics between first-dose and steady-state evaluations were observed. Sputum sampling was incomplete and confounded by previous aerosol administration but revealed colistin concentrations that markedly exceeded observed plasma concentrations. Twenty-one patients experienced one or more side effects attributed to colistin administration. The most common reactions involved reversible neurologic manifestations, including oral and perioral paresthesias (n = 16), headache (n = 5), and lower limb weakness (n = 5). All of these apparent colistin-induced neurologic adverse effects, though bothersome, were benign and reversible. Intermittent proteinuria was observed on urinalysis in 14 patients, and 1 patient developed reversible, colistin-induced nephrotoxicity. No relationship between the occurrence of any colistin-associated adverse effect and plasma colistin concentration or colistin pharmacokinetic parameter estimate was observed. These data provide no basis for routine monitoring of colistin plasma concentrations to guide dosing for patient safety and suggest slow upward dose titration to minimize the incidence and severity of associated side effects.

Safety of antihistamines in children

The histamine H1 receptor antagonists (antihistamines) are an important class of medications used for the relief of common symptoms associated with hyperhistaminic conditions occurring in children and adults. This group of drugs may be subdivided into 3 classes, or generations, based upon their propensity to induce sedation and cardiotoxicity. The first generation (classical) antihistamines are highly effective in treating hyperhistaminic conditions. However, they frequently induce sedation and may adversely affect a child's learning ability. First generation antihistamine-induced sedation has been described to occur in more than 50% of patients receiving therapeutic dosages. Serious adverse events are unusual following overdoses of first generation antihistamines although life-threatening adverse events have been described. When the so-called 'second generation' antihistamines terfenadine and astemizole were introduced they were widely embraced and quickly used by clinicians of all specialities, including paediatricians, as nonsedating alternatives to the first generation compounds. These new agents were found to be equally or more effective than first generation antihistamines in relieving symptoms associated with hyperhistaminic conditions without the soporific effects of the first generation agents. Unfortunately, after approximately 10 years of widespread clinical use, disturbing reports of potentially life-threatening dysrhythmias, specifically torsades de pointes, were described. Both terfenadine and astemizole have been shown in vitro to inhibit several ion channels, and in particular the delayed outward rectifier potassium channel in the myocardium, predisposing the heart to dysrhythmias. The potential life-threatening cardiotoxicities of the second generation antihistamines led to the search for noncardiotoxic and nonsedating agents. Loratadine, fexofenadine, mizolastine, ebastine, azelastine and cetirizine are the first of the new third generation antihistamines. These drugs have been shown to be efficacious with few adverse events including no clinically relevant cytochrome P450 mediated metabolic-based drug-drug interactions or QT interval prolongation/cardiac dysrhythmias. Appropriate treatment of an antihistamine overdose depends upon which class of compound has been ingested. There is no specific antidote for antihistamine overdose and treatment is supportive particularly for ingestions of first generation compounds. Ingestion of excessive doses of terfenadine or astemizole requires immediate medical attention. Children who accidentally ingest excessive doses of a third generation compound may usually be adequately managed at home. However, patients ingesting large amounts (approximately >3 to 4 times the normal therapeutic daily dose) should receive medical attention. These patients should be monitored for 2 to 3 hours after the ingestion and patients ingesting cetirizine should be advised about the potential for sedation. The availability of newer generation antihistamine compounds has clearly added to the clinical effectiveness and patient tolerance of a widely prescribed class of drugs. These advances have also been accompanied by improved safety profiles, particularly in the case of third generation antihistamine overdose.

Review of the pharmacokinetics of cefepime in children

BACKGROUND

Because determining the pharmacokinetics of drugs used in pediatric patients allows for appropriate dosing and optimal clinical response, we have reviewed the pharmacokinetic data on the use of cefepime in the pediatric population.

METHODS

Three studies encompassing 88 patients ages 2 months to 16 years examined the pharmacokinetics of cefepime given as a single iv dose, as multiple iv doses and by im administration. In all studies serial blood and urine or cerebrospinal fluid (CSF) samples were collected after a single dose and/or at steady state, defined as after at least 2 days of dosing. Pharmacokinetic parameters were generated from concentration-vs.-time curves and were analyzed using noncompartmental methods.

RESULTS

In all studies cefepime exhibited a linear pharmacokinetic profile and concentrations declined proportionally over time. Minimal accumulation was observed after multiple dosing. Pharmacokinetic parameters were similar in all studies and appeared to be dose-independent. Mean (range) parameters observed in this review were: t 1/2 = 1.7 h (1.26 to 1.93); volume of distribution at steady state, 0.37 liter/kg (0.33 to 0.40); total body clearance, 3.1 ml/min/kg (1.43 to 4.01); renal total body clearance, 2.3 ml/min/kg (1.86 to 3.05); absolute bioavailability of cefepime after the im dose, 82.3%; and urinary recovery, 72% (57 to 85%). Penetration into CSF appeared to be good, with CSF concentrations averaging 3.3 to 5.7 microg/ml 0.5 and 8 h after administration of the dose, respectively.

CONCLUSION

Cefepime displayed a linear pharmacokinetic profile, was well-absorbed via im injection and had adequate penetration into the CSF of patients with bacterial meningitis, compared with other beta-lactams.

Optimal antibiotic dosing. The pharmacokinetic-pharmacodynamic interface

Successful pharmacotherapy for respiratory tract (and other) infections should integrate both the pharmacokinetic (PK) and the pharmacodynamic (PD) properties of antimicrobial agents. Antibiotics can be classified according to their pattern of antimicrobial activity: concentration-dependent killing, time-dependent killing, or a hybrid pattern. With the concentration-dependent killing pattern, the higher the drug concentration relative to pathogen minimum inhibitory concentration (MIC), the greater the rate and extent of antimicrobial activity. The time-dependent killing pattern is dependent on the duration of pathogen exposure to an antibiotic. The hybrid pattern of antimicrobial activity involves both the duration of pathogen exposure to the antibiotic and a prolonged, persistent post-antibiotic effect. The aminoglycosides and fluoroquinolones exhibit concentration-dependent killing. Thus, the main PK-PD parameters that correlate with their efficacy are the ratio of peak serum drug concentration to MIC and the ratio of the area under the concentration versus time curve to MIC. The percentage of time during the dosing interval that serum drug concentrations exceed the MIC is the only PK-PD parameter that correlates with beta-lactam efficacy. Knowledge of these PK-PD parameters is of value in optimizing the dosing regimens for all antimicrobial agents.

Single dose pharmacokinetics of linezolid in infants and children

BACKGROUND

Linezolid is an oxazolidinone antibiotic with excellent in vitro activity against a number of Gram-positive organisms including antibiotic-resistant isolates. The safety and pharmacokinetics of intravenously administered linezolid were evaluated in children and adolescents to examine the potential for developmental dependence on its disposition characteristics.

METHODS

Fifty-eight children (3 months to 16 years old) participated in this study; 44 received a single 1.5-mg/kg dose and 14 received a single 10-mg/kg dose of linezolid administered by intravenous infusion. Repeated blood samples (n = 10 in children > or = 12 months; n = 8 in children 3 to 12 months) were obtained during 24 h after drug administration, and linezolid was quantitated from plasma by high performance liquid chromatography with mass spectrometry detection. Plasma concentration vs. time data were evaluated with a model independent approach.

RESULTS

Linezolid was well-tolerated by all subjects. The disposition of linezolid appears to be age-dependent. A significant although weak correlation between age and total body clearance was observed. The mean (+/- SD) values for elimination half-life, total clearance and apparent volume of distribution were 3.0 +/- 1.1 h, 0.34 +/- 0.15 liter/h/kg and 0.73 +/- 0.18 liter/kg, respectively. Estimates of total body clearance and volume of distribution were significantly greater in children than historical values of adult data. As such maximum achievable linezolid plasma concentrations were slightly lower in children, and concentrations 12 h after a single 10-mg/kg dose were below the MIC90 for selected pathogens with in vitro susceptibility to the drug.

CONCLUSION

Based on these data a linezolid dose of 10 mg/kg given two to three times daily would appear appropriate for use in pediatric therapeutic clinical trials of this agent.

Nefazodone pharmacokinetics in depressed children and adolescents

OBJECTIVE

To describe the pharmacokinetics and safety of nefazodone (NFZ) in depressed children and adolescents.

METHOD

Depressed youths aged 7 to 17 years were eligible to participate. Intensive sampling for pharmacokinetic analyses of NFZ and 3 of its active metabolites was performed after single and multiple dose administration. Treatment was continued for 6 more weeks and titrated to maximize clinical response.

RESULTS

Twenty-eight patients were enrolled. Systemic exposure to NFZ and 3 metabolites was generally higher in children than adolescents. NFZ and metabolite disposition profiles showed high intra- and interpatient variability. Compared to published data in adults, the half-life of NFZ and 2 of its metabolites appears shorter in children and adolescents. Meta-chlorphenylpiperazine pharmacokinetic parameters were different in 5 patients determined to be poor metabolizers of cytochrome P450 2D6 (CYP2D6). NFZ was well tolerated, and administration was associated with significant reductions (p < .001) in depressive symptoms.

CONCLUSIONS

The pharmacokinetics of NFZ in pediatric patients is highly variable. NFZ appears to be safe in this small, short-term study. Pediatric patients who are poor metabolizers of CYP2D6 do not appear to be at increased risk for NFZ-associated adverse events. Open-label treatment of NFZ is associated with reductions in depressive symptoms.

Evolutionary Timescale of the Pulsating White Dwarf G117-B15A: The Most Stable Optical Clock Known

We observe G117-B15A, the most precise optical clock known, to measure the rate of change of the main pulsation period of this blue-edge DAV white dwarf. Even though the obtained value is only within 1 sigma, P&d2;=&parl0;2.3+/-1.4&parr0;x10-15 s s-1, it is already constraining the evolutionary timescale of this cooling white dwarf star.

Pharmacokinetics of a fluoronaphthyridone, trovafloxacin (CP 99,219), in infants and children following administration of a single intravenous dose of alatrofloxacin

The pharmacokinetics of trovafloxacin following administration of a single intravenous dose of alatrofloxacin, equivalent to 4 mg of trovafloxacin per kg of body weight, were determined in 6 infants (ages 3 to 12 months) and 14 children (ages, 2 to 12 years). There was rapid conversion of alatrofloxacin to trovafloxacin, with an average +/- standard deviation (SD) peak trovafloxacin concentration determined at the end of the infusion of 4.3 +/- 1.4 microg/ml. The primary pharmacokinetic parameters (average +/- SD) analyzed were volume of distribution at steady state (1.6 +/- 0.6 liters/kg), clearance (151 +/- 82 ml/h/kg), and half-life (9.8 +/- 2.9 h). The drug was well tolerated by all children. There were no age-related differences in any of the pharmacokinetic parameters studied. Less than 5% of the administered dose was excreted in the urine over 24 h. On the basis of the mean area under the concentration-time curve of 30.5 +/- 10.1 microg. h/ml and the susceptibility (< or =0.5 microg/ml) of common pediatric bacterial pathogens to trovafloxacin, dosing of 4 mg/kg/day once or twice daily should be appropriate.

Drugs used in the treatment of asthma: a review of clinical pharmacology and aerosol drug delivery

The selection and titration of pharmacologic agents are essential in the treatment of asthma. This Article focuses on the primary medications used in the treatment of reactive airway disease. The recent advances in the technology of devices used to administer aerosolized medications are also reviewed.

Acute encephalopathy due to aluminum toxicity successfully treated by combined intravenous deferoxamine and hemodialysis

Acute aluminum intoxication is uncommon in clinical practice but can be fatal. This limited experience is reflected in the paucity of data assessing a viable approach to the treatment of these patients. In this report, the authors describe the clinical course and successful, pharmacokinetic-based deferoxamine-hemodialysis treatment regimen of a patient with severe aluminum encephalopathy following alum bladder irrigation. The combined use of deferoxamine and appropriately timed hemodialysis appears to be a very reasonable means of treating patients with severe acute aluminum intoxication.