Predicting disruptions to drug pharmacokinetics and the risk of adverse drug reactions in non-alcoholic steatohepatitis patients

The liver plays a central role in the pharmacokinetics of drugs through drug metabolizing enzymes and transporters. Non-alcoholic steatohepatitis (NASH) causes disease-specific alterations to the absorption, distribution, metabolism, and excretion (ADME) processes, including a decrease in protein expression of basolateral uptake transporters, an increase in efflux transporters, and modifications to enzyme activity. This can result in increased drug exposure and adverse drug reactions (ADRs). Our goal was to predict drugs that pose increased risks for ADRs in NASH patients. Bibliographic research identified 71 drugs with reported ADRs in patients with liver disease, mainly non-alcoholic fatty liver disease (NAFLD), 54 of which are known substrates of transporters and/or metabolizing enzymes. Since NASH is the progressive form of NAFLD but is most frequently undiagnosed, we identified other drugs at risk based on NASH-specific alterations to ADME processes. Here, we present another list of 71 drugs at risk of pharmacokinetic disruption in NASH, based on their transport and/or metabolism processes. It encompasses drugs from various pharmacological classes for which ADRs may occur when used in NASH patients, especially when eliminated through multiple pathways altered by the disease. Therefore, these results may inform clinicians regarding the selection of drugs for use in NASH patients.

Attenuated Ochratoxin A Transporter Expression in a Mouse Model of Nonalcoholic Steatohepatitis Protects against Proximal Convoluted Tubule Toxicity

Ochratoxin A (OTA) is an abundant mycotoxin, yet the toxicological impact of its disposition is not well studied. OTA is an organic anion transporter (OAT) substrate primarily excreted in urine despite a long half-life and extensive protein binding. Altered renal transporter expression during disease, including nonalcoholic steatohepatitis (NASH), may influence response to OTA exposure, but the impact of NASH on OTA toxicokinetics, tissue distribution, and associated nephrotoxicity is unknown. By inducing NASH in fast food-dieted/thioacetamide-exposed mice, we evaluated the effect of NASH on a bolus OTA exposure (12.5 mg/kg by mouth) after 3 days. NASH mice presented with less gross toxicity (44% less body weight loss), and kidney and liver weights of NASH mice were 11% and 24% higher, respectively, than healthy mice. Organ and body weight changes coincided with reduced renal proximal tubule cells vacuolation, degeneration, and necrosis, though no OTA-induced hepatic lesions were found. OTA systemic exposure in NASH mice increased modestly from 5.65 ± 1.10 to 7.95 ± 0.61 mg*h/ml per kg BW, and renal excretion increased robustly from 5.55% ± 0.37% to 13.11% ± 3.10%, relative to healthy mice. Total urinary excretion of OTA increased from 24.41 ± 1.74 to 40.07 ± 9.19 µg in NASH mice, and kidney-bound OTA decreased by ∼30%. Renal OAT isoform expression (OAT1-5) in NASH mice decreased by ∼50% with reduced OTA uptake by proximal convoluted cells. These data suggest that NASH-induced OAT transporter reductions attenuate renal secretion and reabsorption of OTA, increasing OTA urinary excretion and reducing renal exposure, thereby reducing nephrotoxicity in NASH. SIGNIFICANCE STATEMENT: These data suggest a disease-mediated transporter mechanism of altered tissue-specific toxicity after mycotoxin exposure, despite minimal systemic changes to ochratoxin A (OTA) concentrations. Further studies are warranted to evaluate the clinical relevance of this functional model and the potential effect of human nonalcoholic steatohepatitis on OTA and other organic anion substrate toxicity.

An overview of plague in the United States and a report of investigations of two human cases in Kern county, California, 1995

Plague was confirmed in the United States from nine western states during 1995. Evidence of Yersinia pestis infection was identified in 28 species of wild or domestic mammals. Thirteen of the plague positive species were wild rodents; 15 were predators/carnivores. Yersinia pestis was isolated from eight species of fleas. Seven confirmed cases of human plague were reported in 1995 (New Mexico 3; California 2; Arizona and Oregon 1 each). Five of the seven cases were bubonic; one was septicemic and one a fatal pneumonic case. Months of onset ranged from March through August. In California, during 1995, plague was recorded from 15 of the 58 counties. Over 1,500 animals were tested, of which 208 were plague positive. These included 144 rodents and 64 predators/carnivores. Two confirmed human cases (one bubonic and one fatal pneumonic) occurred, both in Kern County. Case No. 1 was reported from the town of Tehachapi. The patient, a 23 year-old male resident, died following a diagnosis of plague pneumonia. The patient's source of plague infection could not be determined precisely. Field investigations revealed an extensive plague epizootic surrounding Tehachapi, an area of approximately 500-600 square miles (800-970 square kilometers). Case No. 2 was a 57 year-old female diagnosed with bubonic plague; she was placed on an antibiotic regimen and subsequently recovered. The patient lives approximately 20 miles (32 km) north of Tehachapi. Field investigations revealed evidence of a plague epizootic in the vicinity of the victim's residence and adjacent areas. Overall results of the joint field investigations throughout the entire Kern county area revealed a high rate of plague positive animals. Of the numerous samples submitted, 48 non-human samples were plague positive.

The pharmacokinetics of teicoplanin in infants and children

The pharmacokinetics of teicoplanin were assessed after a single dose and under multidose conditions in 12 infants and children. Study patients ranged in age from 2.4 to 11 years. Each patient received teicoplanin 6 mg/kg body weight given intravenously over 20-30 min, once daily for five consecutive days. Multiple timed blood and urine samples were obtained over the 6 day sampling period and were analysed for teicoplanin by both microbiological assay and HPLC. Three-compartment pharmacokinetic analysis was used to describe the drug's disposition characteristics. Peak and 24 h trough serum teicoplanin concentrations averaged 39.3 and 1.8 mg/L after the first dose with little accumulation observed after 5 days of therapy. Teicoplanin disposition was variable; V(d)ss ranged from 0.31 to 0.68 L/kg, t(1/2)gamma from 6.5 to 18.1 h and CI from 29 to 51 mL/h/kg. A substantial amount of the administered drug distributed rapidly to the largest, third compartment, with egress approximately four-fold slower than ingress. The majority of the drug was excreted unchanged in the urine. Teicoplanin administration was well tolerated by all study subjects. Using the teicoplanin pharmacokinetic data derived in our study, a dose of teicoplanin 8 mg/kg body weight administered every 12 h should achieve target serum trough concentrations averaging 11 mg/L in children. Higher doses, e.g. 15 mg teicoplanin/kg administered every 12 h, may be needed for the treatment of deep-seated staphylococcal infections and/or endocarditis.

Dose-ranging evaluation of bumetanide pharmacodynamics in critically ill infants

OBJECTIVES

Determine the diuretic effects of single intravenous doses of bumetanide in volume-overloaded critically ill infants.

METHODS

A prospective, open-label study was carried out in 56 infants aged 0 to 6 months who required diuretic therapy. Each patient received a single intravenous dose of bumetanide. Doses selected in sequential order ranged from 0.005 to 0.10 mg/kg. Determinations of urine volume, electrolytes, creatinine levels, and osmolality were performed before (collected from -2 to -4 hours to time 0) and at 1, 2, 3, 4, 6, and 12 hours after bumetanide dosing. Serum samples collected at time 0 and at 5, 15, 30, 60, 120, 180, 240, 360, and 480 minutes and urine aliquots collected at time 0, 0 to 1, 1 to 2, 2 to 3, 3 to 4, 4 to 6, and 6 to 12 hours were analyzed for bumetanide concentration. Individual changes in urine flow rate and electrolyte excretion were plotted against corresponding bumetanide excretion rates, taken as the effective dose of the drug.

RESULTS

Peak bumetanide excretion rates increased linearly with increasing doses of drug. Time course patterns for urine flow rate and electrolyte excretion were similar for all dosage groups. Urine flow rate and electrolyte excretion increased linearly up to a bumetanide excretion rate of approximately 7 micrograms/kg/hr and either plateaued (urine flow rate) or declined at a bumetanide excretion rate of > 10 micrograms/kg/hr. Diuretic efficiency of bumetanide was maximal at doses of 0.005 to 0.010 mg/kg but decreased at higher doses.

CONCLUSIONS

Maximal diuretic responses occurred at a bumetanide excretion rate of about 7 micrograms/kg/hr, corresponding to doses of 0.035 to 0.040 mg/kg. Higher doses produced a proportionately higher bumetanide excretion rate but no increased diuretic effect. Lower doses of bumetanide had the greatest diuretic efficiency, suggesting that continuous infusion of low doses of bumetanide or intermittent low-dose boluses may produce optimal diuretic responses in critically ill infants.

Analysis of the variability in the pharmacokinetics and pharmacodynamics of bumetanide in critically ill infants

OBJECTIVES

Account for the interindividual variability in the pharmacokinetics and pharmacodynamics of bumetanide after intravenous administration of single doses to critically ill infants.

METHODS

This prospective open-label study was carried out in the pediatric intensive care unit of a university-based children's hospital. Fifty-three volume-overloaded critically ill infants (age range, 4 days to 6 months) were divided into two groups: those with heart disease (31 infants) and those with lung disease (22 infants). Each patient received a single intravenous bolus dose of bumetanide. Doses, selected in sequential order, ranged from 0.005 to 0.100 mg/kg. Age was used as a continuous variable to determine its effects on the variability in the pharmacokinetics and pharmacodynamics of bumetanide. Hierarchical multiple regression analyses were used to assess the effects of age, disease, and other drugs on the variability in the effects of bumetanide.

RESULTS

Total clearance, renal clearance, and nonrenal clearance of bumetanide all increased with age (p < 0.05), but the ratio of renal clearance to total clearance remained constant at about 0.4. Half-life and mean residence time decreased markedly in the first month of life (p < 0.05). Bumetanide excretion rate normalized for dose also increased with increasing age. Patients with lung disease exhibited a significantly greater clearance and shorter half-life (p < 0.05) than those with heart disease, whereas volume of distribution was similar in both groups. The primary determinant of bumetanide excretion rate was the administered dose (73%). Dose-response curves for urine flow rate and electrolyte excretion were similar between disease groups. The time course of the effect of bumetanide excretion rate on pharmacodynamics responses was similar between disease groups, as was the duration of the diuretic effect.

CONCLUSIONS

The pharmacokinetics of bumetanide were influenced significantly by age and disease. Differences in pharmacokinetics between patients with lung and heart disease were primarily due to differences in total clearance. The administered dose of bumetanide and age were positive determinants of bumetanide excretion rate and pharmacodynamic responses. Pharmacodynamic responses as a function of bumetanide excretion rate were not significantly different between disease groups.

Pharmacokinetics of bumetanide in critically ill infants

OBJECTIVE

Define the pharmacokinetics of bumetanide after single intravenous doses in volume-overloaded critically ill infants.

METHODS

A prospective, open-label study was carried out in a group of 58 infants aged 0 to 6 months who required diuretic therapy. Each patient received a single dose of intravenous bumetanide. Doses selected in sequential order ranged from 0.005 to 0.10 mg/kg. Hematologic and serum chemistry studies were performed before and at 6 and 24 hours after bumetanide administration. Determinations of urine volume and chemistries were performed before (collected from -2 to -4 hours to time 0) and at 1, 2, 3, 4, 6, and 12 hours after bumetanide dosing. Serum samples collected at time 0 and at 5, 15, 30, 60, 120, 180, 240, 360, and 480 minutes and urine collected at time 0 and at 0 to 1, 1 to 2, 2 to 3, 3 to 4, 4 to 6, and 6 to 12 hours were analyzed for bumetanide concentration. Data were evaluated by standard noncompartmental pharmacokinetic techniques.

RESULTS

Peak serum bumetanide concentrations occurred at 5 minutes after bumetanide administration. Area under the curve and peak serum bumetanide concentrations showed linear increases over the twentyfold dose range; whereas beta volume of distribution, volume of distribution at steady state, clearance, renal clearance, half-life, and mean residence time values were independent of dose. Peak urinary excretion rates of bumetanide increased linearly with increasing doses. The mean percent of bumetanide recovered in the urine from 0 to 12 hours was 40% +/- 15% of the administered dose.

CONCLUSIONS

Distribution and elimination kinetics of bumetanide were similar in all patients. Elimination kinetics were first order over the dose range of 0.005 to 0.10 mg/kg. Pharmacokinetic parameter estimates (beta volume of distribution, volume of distribution at steady state, clearance, renal clearance, half-life, and mean residence time) were independent of the dose of bumetanide administered. Single doses of bumetanide up to 0.10 mg/kg appear to be well tolerated in acutely ill volume-overloaded infants aged 0 to 6 months.

A pharmacokinetically based propofol dosing strategy for sedation of the critically ill, mechanically ventilated pediatric patient

OBJECTIVE

To assess the pharmacokinetics and pharmacodynamics of propofol sedation of critically ill, mechanically ventilated infants and children.

DESIGN

A prospective clinical study.

SETTING

A pediatric intensive care unit (ICU) in a university hospital.

PATIENTS

Clinically stable, mechanically ventilated pediatric patients were enrolled into our study after residual sedative effects from previous sedative therapy dissipated and the need for continued sedation therapy was defined. Patients were generally enrolled just before extubation.

INTERVENTIONS

A stepwise propofol dose escalation scheme was used to determine the steady-state propofol dose necessary to achieve optimal sedation, as defined by the COMFORT scale, a validated scoring system which reliably and reproducibly quantifies a pediatric patient's level of distress. When in need of continued sedation, study patients received an initial propofol loading dose of 2.5 mg/kg and were immediately started on a continuous propofol infusion of 2.5 mg/kg/hr. The propofol infusion rate was adjusted and repeat loading doses were administered, if needed, using a coordinated dosing scheme to maintain optimal sedation for a 4-hr steady-state period. After 4 hrs of optimal sedation, the propofol infusion was discontinued and simultaneous blood sampling and COMFORT scores were obtained until the patient recovered. Additional blood samples were obtained up to 24 hrs after stopping the infusion and analyzed for propofol concentration by high-performance liquid chromatography.

MEASUREMENTS AND MAIN RESULTS

Twenty-nine patients were enrolled into this study. One patient was withdrawn from this study because of an acute decrease in blood pressure occurring with the first propofol loading dose; 28 patients completed the study. All patients were sedated immediately after the first 2.5-mg/kg propofol loading dose. Eight patients were adequately sedated with the starting propofol dose regimen, whereas five patients required downward dose adjustment and 11 patients required dosage increases to achieve optimal sedation. Four patients failed to achieve adequate sedation after five dose escalations and the drug was stopped. Recovery from sedation (COMFORT score of > or = 27) after stopping the propofol infusion was rapid, averaging 15.5 mins in 23 of 24 evaluable patients. In 13 patients who were extubated after stopping the propofol infusion, the time to extubation was also rapid, averaging 44.5 mins. Determination of the blood propofol concentration at the time of recovery from propofol sedation was possible in 15 patients. The blood propofol concentration was variable, ranging between 0.262 to 2.638 mg/L but < or = 1 mg/L in 13 of 15 patients. Similarly, tremendous variation was observed in propofol pharmacokinetics. Propofol disposition was best characterized by a three-compartment model with initial rapid distribution into a small central compartment, V1, and two larger compartments, V2 and V3, which are two-and 20-fold greater in volume, respectively, than V1. Redistribution from V2 and V3 into V1 was much slower than ingress, underscoring the importance of the propofol concentration in V1 as reflective of the drug's sedative effect. Propofol was well tolerated. Two patients experienced an acute decrease in blood pressure which resolved without treatment.

CONCLUSIONS

We conclude that a descending propofol dosing strategy, which maintains the propofol concentration constant in the central compartment (V1) while drug accumulates in V2 and V3 to intercompartmental steady-state, is necessary for effective propofol sedation in the pediatric ICU. Our proposed dosing scheme to achieve and maintain the blood propofol concentration of 1 mg/L would appear effective for sedation of most clinically stable, mechanically ventilated pediatric patients.

Dermoids of the eustachian tube: CT and MR findings with histologic correlation

Two patients with congenital dermoids of the eustachian tube presented with recurrent otitis media and chronic otorrhea resistant to antimicrobial therapy. CT demonstrated fat density, homogeneous lesions, filling and expanding the eustachian tube. On MR, signal from the lesions was consistent with fat, and the relationship with the internal carotid artery was better delineated than by CT. Microscopically, the masses consisted of a conglomeration of ectodermal and mesodermal elements.

Clinical pharmacology of imipenem and cilastatin in premature infants during the first week of life

The first-dose and multidose pharmacokinetics of imipenem and cilastatin were evaluated in 41 premature infants during their first week of life. Premature infants (gestational age, less than or equal to 37 weeks) were assigned to receive 10-, 15-, 20-, or 25-mg/kg doses of imipenem-cilastatin (1:1) as a single- or multiple-dose regimen. A total of 39 infants received a single dose, whereas 18 infants received multiple doses. No differences were observed in pharmacokinetic parameter estimates for either agent relative to the dose administered or infant body weight; thus, the data were pooled. Elimination half-life, steady-state volume of distribution, and body clearance averaged 2.5 h, 0.5 liter/kg, and 2.5 ml/min per kg, respectively, for imipenem and 9.1 h, 0.4 liter/kg, and 0.5 ml/min per kg, respectively, for cilastatin. Similar values for these parameter estimates were observed after multidose administration, although substantial accumulation of cilastatin in serum was observed. A total of 21% of the imipenem and 43% of the cilastatin were excreted unchanged in the urine over a 12-h collection period. Corresponding renal clearances averaged 0.4 and 0.2 ml/min per kg for imipenem and cilastatin, respectively. Substantial differences were observed in the route by which imipenem was cleared from the body compared with data from adult volunteers. These data suggest that infants should receive an imipenem dose of 20 mg/kg administered every 12 h for the treatment of bacterial infections outside the central nervous system.

Embryonic development of the innervation of the locust extensor tibiae muscle by identified neurons: formation and elimination of inappropriate axon branches

Intracellular dye fills have been used to reveal the pattern of embryonic growth of each of the four neurons which innervate the extensor tibiae muscle (ETi) of the hind leg of the locust. The growth cone of the slow extensor tibiae motoneuron (SETi), the first of the four neurons to leave the central nervous system, pioneers nerve 3 (N3). The fast extensor motoneuron (FETi), the next neuron to grow out, follows earlier outgrowing motoneurons into the periphery in nerve 5 (N5) and then rejoins SETi in N3. As it transfers from N5 to N3, it is transiently dye-coupled to the Tr1 pioneer neuron which spans the gap between the two nerves. It then follows SETi onto the ETi muscle in the femur. The common inhibitory neuron and the dorsal unpaired median neuron (DUMETi) follow SETi and FETi in nerves 3B2 and 5B1, respectively. SETi's growth cone requires almost twice as long to reach ETi as those of the three later motoneurons, all of which follow preexisting neural pathways. At least three of the four developing motoneurons form one or more axon branches not found in the adult. These branches may occur (1) at segmental boundaries; (2) where the nerve, which the growth cone is following, itself branches or the growth cone encounters another nerve; or (3) when the axon continues to grow beyond its target muscle. These findings contrast with the apparent absence of inappropriate axon branches in another developing locust neuromuscular system and during the innervation of zebrafish myotomes, but resemble in some ways the transient production of inappropriate axonal branches reported for embryonic leech motoneurons.

Lack of unique ciprofloxacin pharmacokinetic characteristics in patients with cystic fibrosis

The single-dose pharmacokinetics of oral ciprofloxacin 750 mg were evaluated in six subjects with cystic fibrosis (CF subjects) and six age, sex and approximate weight-matched control subjects (controls). In addition, the effect of concurrently administered oral pancreatic enzyme replacement on the pharmacokinetics of ciprofloxacin was studied in 12 CF subjects. Ciprofloxacin t1/2, VSSF, CLF, and CLR in the matched CF subjects averaged 4.5 hours, 2.8 L/kg, 2.73 mL/min/kg and 5.7 mL/min/kg, respectively. Forty-two percent of the ciprofloxacin dose was excreted in the urine (0-48 hours) as the parent compound. No statistically significant differences in these ciprofloxacin pharmacokinetic parameter estimates were observed between CF and control subjects. In three CF subjects and two controls, the urinary excretion of ciprofloxacin and four of its metabolities were similar. In contrast, CF subjects demonstrated a prolonged tmax (2.3 versus 1.3 hours P less than .05) though ciprofloxacin Cmax was similar (4.7 versus 3.8 mg/L, NS). The concurrent administration of oral pancreatic enzyme replacement had no effect on the pharmacokinetics of ciprofloxacin. Apparent ciprofloxacin pharmacokinetic parameters in sputum were similar to those observed in serum. Sputum ciprofloxacin concentrations lagged behind serum concentrations but, on average, exceeded serum concentrations for 20 hours of the 24-hour sampling period. These sputum ciprofloxacin concentrations exceeded the reported MIC90 for Pseudomonas aeruginosa for approximately 15 hours. These data suggest an oral ciprofloxacin dose of 750 mg administered q8h to promote accumulation and maintenance of sputum drug concentrations well above pathogen MICs for the majority of a dosing interval in patients with CF.

High-performance liquid chromatography of ciprofloxacin and its metabolites in serum, urine and sputum

A versatile and sensitive method requiring no internal standard was developed for quantitating ciprofloxacin in serum, urine and sputum by high-performance liquid chromatography with fluorescence detection. Acetonitrile and chloroform were employed to remove protein and lipophilic substances from an aqueous, ciprofloxacin-containing sample layer. The proportions of acetonitrile and 0.1 M potassium phosphate, pH 2.5, in the mobile phase were varied to suit the purpose of the assay. For the routine determination of ciprofloxacin pharmacokinetics, isocratic 19% acetonitrile was used. A gradient from 15 to 35% acetonitrile was chosen to show the appearance of metabolites which formed during the biodisposition of ciprofloxacin. In the latter case urine samples were diluted for assay and protein was precipitated from serum samples with trichloroacetic acid. Four fluorescent metabolites were observed in all patient specimens, and with tandem ultraviolet detection two additional ultraviolet-absorbing metabolites were readily found in urine specimens.

Ciprofloxacin monotherapy for acute pulmonary exacerbations of cystic fibrosis

Ciprofloxacin has potent in vitro activity against Pseudomonas aeruginosa and Pseudomonas cepacia strains isolated from cystic fibrosis patients. Our previous single-dose pharmacokinetic and pharmacodynamic studies identified important differences between cystic fibrosis patients and age- and sex-matched controls. Based on these data, 30 acutely ill cystic fibrosis patients (aged 18 to 44 years) received 750 mg of ciprofloxacin orally every eight hours for 21 days. Multiple timed serum, urine, and sputum samples for pharmacokinetic analysis were obtained on Days 3, 12, 14, and 21 of the study. Estimates of steady-state pharmacokinetic parameters averaged (+/- SD): t1/2 beta, 3.8 (1) hours; Vd/F, 4.4 (2) liters/kg; Cl/F, 772.9 (301) ml/minute/1.73 m2; Fe, 46 percent; peak, 5.4 (2) mg/liter; and trough, 1.8 (0.8) mg/liter. Serum ciprofloxacin concentrations and pharmacokinetic estimates remained unchanged throughout the study. Sputum ciprofloxacin concentrations exceeded those observed in serum. Sputum cultures revealed 43 P. aeruginosa (MIC90 = 2 micrograms/ml) and 15 P. cepacia (MIC90 = 16 micrograms/ml) strains. Sputum ciprofloxacin concentrations exceeded the MIC90 for P. aeruginosa approximately fivefold, yet only eight isolates were fully suppressed. Posttreatment sputum cultures revealed 35 P. aeruginosa (MIC90 = 16 micrograms/ml) and 15 P. cepacia (MIC90 = 16 micrograms/ml). All patients showed clinical improvement based upon the results of pulmonary function tests and an acute clinical efficacy score (median pre 49/post 60). No patients experienced drug-related toxicity. Ciprofloxacin monotherapy is effective for the acute treatment of cystic fibrosis patients. The development of pathogen resistance during oral therapy may limit its utility in ambulatory patients.

Therapeutic evaluation of piperacillin for acute pulmonary exacerbations in cystic fibrosis

The efficacy and pharmacokinetics of piperacillin monotherapy were studied in 46 patients with cystic fibrosis. Two patients were dropped from the study within 24 hr of enrollment because of drug-associated nausea and vomiting. Initially fourteen older patients (greater than 12 years) receiving piperacillin 450 mg/kg/day underwent a preliminary evaluation. Based on the results, 30 younger patients (less than or equal to 12 years) randomized in a double-blind fashion received either 600 or 900 mg/kg/day of piperacillin in six divided doses. Pharmacokinetic parameter estimates for t1/2 Vdss, and Cl were similar for first dose and steady-state evaluations. In 27 patients, approximately 43% of the administered dose was recovered in the urine after 4 hr. Piperacillin CiR averaged 49% of the total Cl. No difference in overall clinical efficacy could be identified between 600 and 900 mg/kg/day of piperacillin using two different objective scoring systems. Although a reduction in sputum Pseudomonas colony counts was greater following the 900 mg/kg/day regimen, this appeared to be independent of clinical effect. In 14 patients (32%), a distinct adverse serum-sicknesslike reaction was observed. The incidence of this reaction appeared to increase as the dose of piperacillin increased. All signs and symptoms of this reaction resolved within 36 hr of discontinuing piperacillin administration but recurred immediately on rechallenge in four patients. All patients with the adverse reaction were subsequently treated with beta-lactam antibodies without ill effect. Overall, clinical improvement appeared to be independent of the piperacillin dose. Our data support the use of total daily piperacillin dosages not exceeding 600 mg/kg.

Single-dose pharmacokinetics of aztreonam in children with cystic fibrosis

The single-dose pharmacokinetics of aztreonam was evaluated in 10 clinically stable subjects with cystic fibrosis. Each child received 30 mg aztreonam/kg intravenously over 2 to 3 minutes. Multiple timed blood samples were obtained over 8 hours for determination of aztreonam elimination kinetics; all urine excreted for 24 hours was collected in timed aliquots for the determination of aztreonam and its microbiologically inactive metabolite, SQ 26,992. Aztreonam pharmacokinetic parameters were determined by model-independent methods. Mean t1/2, steady-state volume distribution, and body clearance were 1.3 hr, 0.25 L/kg, and 127.2 ml/min/1.73m2, respectively. In 9 of the 10 subjects, two-compartment pharmacokinetic analysis was possible and compared favorably with model-independent parameter estimates. Twenty-four-hour urinary recovery of aztreonam was 76.3% of the administered dose; 2.6% was recovered as the metabolite SQ 26,992. The renal clearance of aztreonam averaged 92.5 ml/min/1.73m2. When these data are combined with in vitro susceptibility data for aztreonam against Pseudomonas aeruginosa isolated from the sputum of patients with cystic fibrosis, a dose of 200 mg aztreonam/kg/day divided six hourly would be predicted to maintain serum concentrations above the minimum inhibitory concentration (MIC) for these organisms for the majority of the dosing interval.

Cephalosporin therapeutics in cystic fibrosis

Cephalosporins modified at the C-3 and C-7 positions of the cephem-nucleus have high antimicrobial activity and are safe. With evolution through first, second, and third generations, they have gained increasing gram-negative activity, but often at the expense of potency against gram-positive organisms. All third-generation cephalosporins have some intrinsic anti-Pseudomonas activity, indicating their potential benefit in the treatment of acute pulmonary exacerbations in patients with cystic fibrosis. Rational therapy in this clinical setting requires recognition of the pharmacodynamic and pharmacokinetic idiosyncrasies intrinsic to this patient population. When these priorities are recognized, only two of the available agents, cefsulodin and ceftazidime, appear to be of any therapeutic value. Both agents have been evaluated extensively in the treatment of acute pulmonary exacerbation in cystic fibrosis, and both have been found to be safe and effective.

Developmental pharmacology and therapeutics of piperacillin in gram-negative infections

Twenty children ranging in age from 1 week to 19 years with documented or suspected bacterial infections arising outside the central nervous system were studied. Pharmacokinetic analysis was possible in 15 children; 8 after the first dose, 6 during steady-state conditions, and 4 on both occasions. Data were obtained utilizing noncompartmental pharmacokinetic methods. Peak piperacillin serum concentrations ranged from 51 to 232 mg/l and correlated directly (r = 0.75) with the dose administered. In children with normal renal function, there was an age-dependent decrease in elimination half-life and apparent steady-state volume of distribution, whereas plasma clearance increased logarithmically. All but 1 child responded favorably to piperacillin therapy, and 1 child with a urinary tract infection relapsed 10 days after discontinuation of the therapy. Although improved clinically, piperacillin monotherapy failed to eradicate pathogens in 2 children. No adverse clinical or biochemical effects were observed in any child.

Pharmacokinetic determination of ranitidine pharmacodynamics in pediatric ulcer disease

The pharmacokinetics and pharmacodynamics of ranitidine were evaluated during three methods of administration in 12 children ranging in age from 3.5 to 16 years with documented gastric or duodenal ulcer disease. First, a continuous intravenous infusion of ranitidine was administered to determine the serum concentration necessary to suppress gastric acid secretion by at least 90%. From these data a therapeutic dose of ranitidine was calculated and administered on separate days via the intravenous bolus and oral routes. Half-life, volume of distribution, and clearance values for ranitidine were the same after intravenous bolus and oral doses (1.8 vs 2.0 hours, 2.3 vs 2.5 L/kg, and 794.7 vs 788.0 ml/min/1.73 m2, respectively). The bioavailability of ranitidine given orally averaged 48%. Serum ranitidine concentrations necessary to inhibit gastric acid secretion by at least 90% ranged between 40 and 60 ng/ml for all children studied. No adverse clinical or biochemical effects were observed in any child during the 6 weeks of orally administered treatment. Endoscopic reevaluation after 6 weeks indicated complete healing of initial ulcers.

The distribution of bovine pancreatic polypeptide/FMRFamide-like immunoreactivity in the ventral nervous system of the locust

The distribution of bovine pancreatic polypeptide (BPP) FMRFamide-like immunoreactivity is described in the ganglia of the ventral nerve cord and in the peripheral median nervous system of the locust, Schistocerca gregaria. Immunoreactive cell bodies occur in three regions of the thoracic ganglia: 1) two pairs of cells lie in the anterior of the ganglion ventral to the root of nerve 1 and the anterior ventral association centre; 2) a group of cells lies in the ventral midline at the level at which nerves 3 and 4 leave the ganglion; 3) and two bilaterally symmetrical, posterior lateral groups lie between nerves 5 and 6 at the edge of the ganglion. Immunoreactive cell bodies in the suboesophageal and abdominal ganglia are confined to the midline and are distributed along the anterior-posterior axis both dorsally and ventrally. The processes of the posterior lateral groups have been traced into the neurohaemal organs of the median nerve and beyond. In the periphery such processes innervate the salivary glands and various muscles. The nature of the endogenous antigen contained in the immunoreactive cells has been investigated with the use of antisera against other peptides of the pancreatic polypeptide family, namely avian pancreatic polypeptide, neuropeptide Y, and peptide YY. In addition, BPP antisera not specific for the C terminal hexapeptide have been tested. Liquid preabsorption experiments with BPP and FMRFamide (the molluscan cardioacceleratory peptide) suggest that the endogenous peptide antigen contained in the stained neurones may belong to the pancreatic polypeptide family or to the FMRFamide family.

Pharmacokinetics of imipenem and cilastatin in patients with cystic fibrosis

The pharmacokinetics of imipenem, a new carbapenem antibiotic, and cilastatin, a metabolic inhibitor, were evaluated in 17 patients with cystic fibrosis. Imipenem and cilastatin were combined in a ratio of 1:1 in the infusion solution, and patients intravenously received 30, 60, or 90 mg of imipenem per kg of body weight per day, divided into four equal doses. Pharmacokinetic evaluation after the first dose and again under steady-state conditions revealed biodisposition characteristics which were similar and independent of the daily dose administered. Cilastatin concentrations in serum paralleled those of imipenem. A linear relationship between dose and area under the serum concentration-time curve for both compounds was observed, suggesting a first-order pharmacokinetic process. A total of 50 and 78% of the doses of imipenem and cilastatin, respectively, were recovered unchanged in the urine. The renal clearances of imipenem and cilastatin averaged 54 and 88%, respectively, of the serum clearance. These data suggest that an extrarenal mechanism may be involved in the overall elimination of imipenem. No patient experienced any clinical or biochemical abnormalities during drug therapy.

Pharmacokinetics and cerebrospinal fluid penetration of ceftazidime in children with meningitis

The single dose pharmacokinetics and cerebrospinal fluid (CSF) penetration of ceftazidime were determined in 10 children with bacterial meningitis. Serum ceftazidime pharmacokinetics showed a distinct age dependence in which the clearance in children less than 1 month of age was markedly reduced. Ceftazidime concentrations in CSF, which ranged from 1.4-8.5 micrograms/ml, exceeded the minimum bactericidal concentrations for infecting pathogens throughout the 8-hour sampling period. These concentrations were found to be independent of CSF cell count, protein concentration or the day of therapy on which the study was performed. The ratio of CSF to serum ceftazidime concentration increased with time, suggesting that ceftazidime was cleared more slowly from CSF than from peripheral blood. Our data support the initiation of a study comparing the efficacy of ceftazidime to conventional therapy in children with bacterial meningitis.

Determination of imipenem and cilastatin in serum by high-pressure liquid chromatography

Imipenem and cilastatin concentrations in serum were determined by using reverse-phase high-pressure liquid chromatography. Serum samples were stabilized with 0.5 M morpholineethanesulfonic acid buffer (pH 6.0) and subjected to ultrafiltration before chromatography. The elution solvent consisted of water or potassium phosphate buffered to pH 2.5 and methanol. The imipenem and cilastatin peaks were detected at 300 and 220 nm, respectively. Recovery from serum was 99% for both imipenem and cilastatin, and the limits of detectability for the two compounds were 0.3 and 0.5 microgram/ml, respectively. The assay may be readily applied to pharmacokinetic analysis of imipenem and cilastatin biodisposition in patients.

Single-dose pharmacokinetics of cefsulodin in patients with cystic fibrosis

The single-dose pharmacokinetics of cefsulodin were evaluated in 12 patients with cystic fibrosis. Each patient received 3 g of cefsulodin intravenously over 30 min. Multiple plasma and urine samples were obtained during the 6-h study period for the determination of cefsulodin. Pharmacokinetic parameters were determined by model-independent methods. Mean values for t1/2, Vss, and CLp were 1.53 h, 0.242 liters/kg, and 117.3 ml/min per 1.73 m2, respectively. Six-hour urine recovery revealed 73.2% of the administered dose with a corresponding cefsulodin urinary clearance of 75.1 ml/min. These pharmacokinetic data in patients with cystic fibrosis appear consistent with data reported for unaffected individuals.

Modification of the theophylline radioimmunoassay

The routine utilization of a commercially available radioimmunoassay (RIA) for theophylline (GammaDab), although reliable, is currently prohibited by the high cost of the reagents. In an effort to reduce these costs we have diluted the [125I]theophylline tracer and theophylline antiserum reagents by one-half, contrary to the manufacturer's recommendations. We have demonstrated that an excellent correlation exists (r = 0.968) between our modified RIA method and a conventional high-performance liquid chromatographic technique, despite reagent dilution. Accordingly, our reagent costs have been reduced by half. We conclude that the GammaDab kit reagents can be diluted twofold and still provide an accurate determination of serum theophylline. We must also emphasize that any further alteration(s) of this theophylline RIA procedure would require a thorough evaluation before its routine use could be substantiated.

Determination of cefsulodin in biological fluids by high-pressure liquid chromatography

Cefsulodin is a third-generation cephalosporin with a unique specificity for Pseudomonas aeruginosa. To study the pharmacokinetics of this agent in children, a rapid and sensitive high-performance liquid chromatographic micromethod was developed for plasma and urine. Protein was precipitated from plasma with one volume of cold methanol, and 20 microliter of the resulting supernatant solution was injected into a Zorbax C-8 reversed-phase column. The mobile phase was composed of 4.5 parts acetonitrile and 95.5 parts of 0.035 M ammonium acetate buffer (pH 5.2). Flow rate was 1.0 ml/min and peaks were detected at 265 nm. A flow gradient from 0.3 to 2.0 ml/min over 34 min was employed for urine. The analysis had a limit of detectability of 1 microgram/ml and a between-day coefficient of variation of 4.4 and 5.0 for 100 and 10 micrograms/ml samples, respectively.

Dosing implications of rapid elimination of trimethoprim-sulfamethoxazole in patients with cystic fibrosis

The first-dose and steady-state pharmacokinetics of trimethoprim and sulfamethoxazole were determined in 14 patients with cystic fibrosis. When pharmacokinetic data from the first dose were compared with those at steady state, both TMP and SMZ showed expected accumulations in serum concentrations and decreases in total body clearance. The area under the SMZ serum concentration-time curve was significantly greater at steady state, suggesting drug accumulation during long-term therapy. When pharmacokinetic characteristics for TMP and SMZ obtained in patients with cystic fibrosis were compared with those reported for normal adults, the patients were found to have shorter elimination half-lives and greater plasma clearances. In addition, the apparent volume of distribution for TMP was smaller for patients with cystic fibrosis than for normal adults, consistent with their reduced mass of adipose tissue. Our data support the need for increased dosing or decreased dosing intervals when administering TMP-SMZ to patients with cystic fibrosis.

Single-dose plasma and cerebrospinal fluid pharmacokinetics of ceftriaxone in infants and children

Pharmacokinetic variables were studied in children with central nervous system infections who received a single dose of ceftriaxone sodium. After initial lumbar puncture of children with documented or suspected bacterial meningitis, ventriculitis, or both, therapy was initiated with i.v. ampicillin and chloramphenicol. Children were randomly selected to receive a single i.v. dose of ceftriaxone. Concentrations of ceftriaxone were measured in plasma at intervals from 0 to 720 minutes after the beginning of the infusion and in cerebrospinal fluid (CSF) at one to five hours after the dose. Blood samples were obtained immediately after the second lumbar puncture for assessment of drug penetration into CSF. Elimination rate constant, elimination half-life, apparent volume of distribution, and plasma clearance were determined from samples obtained 30-720 minutes after the start of the infusion. In two children with ventriculoperitoneal shunts, serial determinations of ceftriaxone in CSF were obtained. All eight children who received 75 mg/kg and five of eight who received 50 mg/kg had positive CSF cultures. Volume of distribution was less after the 50 mg/kg dose than after the 75 mg/kg dose. In the children with shunts, adequate CSF drug concentrations were maintained throughout 12 hours of testing. These data support a 12-hour dosage interval, but clinical studies are needed to evaluate efficacy of the drug at both 12-hour and 24-hour dosage regimens.

Determination of amiodarone and its N-deethylated metabolite in serum by high-performance liquid chromatography

A high-performance liquid chromatographic (HPLC) method utilizing hexane extraction and a normal bonded phase column (NH2-alkylamine) was developed to measure serum concentrations of amiodarone and its N-deethylated metabolite. A single analysis requires 8 min. The one-step extraction efficiencies of amiodarone and the internal standard are greater than 90%. The method is linear between 0.05 and 20.0 micrograms/ml. The average relative standard deviation of the slope of the standard curve is 4% and the single day coefficient of variation is 3.2%. The use of hexane extraction for sample cleanup and a bonded phase column for chromatography result in a sensitive and reproducible system well suited to laboratories monitoring serum concentrations of multiple drugs by HPLC. A preliminary study has shown the assay to be useful for the investigation of the pharmacokinetics of this agent.

Developmental pharmacokinetics of moxalactam

A pharmacokinetic evaluation of moxalactam was performed with 30 infants and children with documented or suspected bacterial infections arising outside the central nervous system. Each child received 50 mg of moxalactam per kg infused intravenously over a period of 15 min every 8 h. A total of 26 children were studied after receiving the first dose; 20 of these, along with 4 additional patients, were evaluated after receiving continuous therapy for at least 3 days. After the first dose, the elimination half-life, apparent volume of distribution, and plasma clearance averaged 1.59 h, 0.331 liter/kg, and 100.9 ml/min per 1.73 m2, respectively. The biodisposition of the moxalactam epimers was also evaluated, with similar overall results. No differences in pharmacokinetic parameters were observed when the first-dose values were compared with those obtained at the steady state. Age-dependent changes in moxalactam elimination were observed for children of less than or equal to 1 year of age, suggesting that a dosage reduction may be necessary for children of less than or equal to 2 months of age.

Determination of ceftazidime in biological fluids by using high-pressure liquid chromatography

Ceftazidime is a new beta-lactamase-stable third-generation cephalosporin with a broad spectrum of antimicrobial activity. To evaluate the biodisposition of the drug in infants and children, a rapid and simple high-pressure liquid chromatographic technique was developed. The method is useful for both serum and urine and involves methanol precipitation followed by reverse-phase chromatography on MicroPak MCH 10. The mobile phase, consisting of 20% methanol and an 80% aqueous solution of 50 mM ammonium dihydrogen phosphate and 117 microM perchloric acid, is pumped at 1 ml/min through the column which is maintained at 50 degrees C. The drug was detected at 257 nm with a variable-wavelength UV detector. A good linear correlation was observed between the peak area and the ceftazidime concentration at 0.3 to 500 micrograms/ml (r = 0.999). Since an equal volume of cold methanol is used to precipitate proteins from serum samples and only 20 microliters of the resultant supernatant is injected into the column, samples as small as 50 microliters may be routinely analyzed. This method has been used to study ceftazidime pharmacokinetics in more than 30 patients and has proven to be rapid and reproducible.

Ceftazidime in cystic fibrosis: pharmacokinetics and therapeutic response

The pharmacokinetics of ceftazidime were assessed following a single-dose in 20 patients (8 to 30 years) with cystic fibrosis. All patients received 50 mg/kg (0.9 to 3.5 g) bolus over 30 to 60 sec. Multiple timed samples were obtained over 8 h and analysed by a sensitive HPLC technique. Two-compartment pharmacokinetic analysis revealed means (+/- S.D.) T 1/2 alpha, 0.45 (0.20) h; T 1/2 beta, 1.74 (0.63) h; Vd, 270.0 (50.0) ml/kg; Vc, 190.0 (50.0) ml/kg and Cl beta, 133.7 (22.8) ml/min/1.73 m2. Probenecid pretreatment in six patients was without effect on T 1/2 beta and Cl beta. Urinary excretion was (% of dose) 0 to 2 h, 65.4 (11.1); 2 to 4 h, 14.9 (3.4) and 4 to 8 h, 9.8 (5.8). Ceftazidime was used to treat pulmonary exacerbations in 12 adult cystic fibrosis patients with multiply-resistant Pseudomonas species. Each patient received 2 g iv 8-hourly for 14 to 35 days. Ten of 12 patients showed dramatic improvement as determined by increased appetite and weight gain and arterial pCO2. No hepatic, renal or bone-marrow toxicity was noted. Ceftazidime is an effective antipseudomonal agent possessing favourable pharmacokinetic characteristics with potential use in the treatment of pulmonary exacerbations in cystic fibrosis.

The dexamethasone suppression test in mania

The results of the overnight 2 mg Dexamethasone Suppression Test administered to 50 manic patients are reported. Twenty-three (46%) cases showed an absence of normal suppression, results which are similar to those seen in endogenous depression and which differ to those of others who have all reported normal suppression in mania. Suppressors and non-suppressors were not shown to differ in the factors of age, weight, polarity or the rated severity of mood.

Alterations in gentamicin pharmacokinetics during neonatal exchange transfusion

The effect of double volume exchange transfusion on the pharmacokinetics of gentamicin was studied in 7 neonates undergoing eight transfusions. The procedures were performed an average of 9.6 h following the previous dose of drug and required an average of 0.91 h to complete. Exchange transfusion decreased serum gentamicin concentrations by 18.5 +/- 4.2% and increased the elimination rate for gentamicin by 31.8%. Serum concentrations obtained an average of 3.3 h following the procedure showed a rebound increase in concentration compared to that obtained just at the end of the transfusion (2 cases), no change (1 case) or a decrease compared with the immediate posttransfusion period (5 cases). The results observed in the late posttransfusion period were found to be inversely related (r = -0.78) to the number of doses received by the patient prior to the procedure. A one-compartment pharmacokinetic model was found to be adequate in predicting the amount of drug removed by the procedure while a two-compartment model best described the posttransfusion alteration in elimination kinetics.

The inheritance of yellow-larva and ruby-eye in Culex pipiens

It has been suggested that mosquito vectors of filariasis and other diseases might be controlled by genetic methods. This is not yet possible because of the lack of genetic information concerning the vector species. The present study describes the development of a marker strain which is being used to study genetic control.Two spontaneous mutants of Culex pipiens are described, one for the first time. Ruby-eye (ru) is an autosomal recessive in linkage group 2. It is completely penetrant and completely expressed. It is evident in later instar larvae, pupae, and adults. Yellow-larva (y) is an autosomal recessive, sometimes behaving as a partial dominant, and is also in linkage group 2. It is evident in late fourth-instar larvae and pupae and is generally associated with lengthened larval development. Ruby-eye and yellow-larva are occasionally seen in collections from the field. The frequency of crossing over between ru and y differs significantly among progenies and also between the sexes, the median values being 17% in males and 24% in females.