Increased cancellous bone remodeling during lactation in beagles

Changes in bone mass and cancellous bone remodeling parameters were determined during lactation in adult beagles. Bone mineral content was determined by photon absorptiometry, fraction of mineralized cancellous bone area and perimeter to area ratios by image analysis of microradiographs, and bone remodeling parameters by fluorochrome-based histomorphometry. Bone mineral content of the intact proximal humerus and fraction of mineralized tissue areas of lumbar vertebral cancellous bone were decreased during lactation when compared with controls. There were significant increases during lactation in osteoid volumes and osteoid surface, although osteoid seam thickness was not changed. There were significant increases in the fraction of fluorochrome-labeled cancellous bone surfaces in the lactating dogs when compared with controls. The mineralizing surface, bone formation rate and activation frequency were significantly increased in the lactating dogs when compared with controls. There were also significant increases in resorption parameters during lactation. These data indicate that during lactation, bone remodeling and bone turnover is increased. Increased bone remodeling during lactation in a longer-lived mammal may represent an example of a "reversible mineral deficit" which may be an important physiological mechanism in nursing mothers to ensure adequate calcium for milk production. Increased bone remodeling may also provide a physiological mechanism to enhance the capacity of the skeleton to better accommodate the greatly increased and episodic changes in mineral homeostasis during lactation.

Localization and measurement of neurotransmitter receptors in rat and human brain by quantitative autoradiography

Receptors for neurotransmitters can be visualized and characterized using in vitro tissue slice binding techniques and quantitative autoradiography. In this article, the general methods used in studies of this type are outlined and specific application to the study of catecholamine and neuropeptide receptors in rat and human brain tissue are described. Receptor autoradiography is used to examine regulation of dopamine receptor density in response to denervation and replacement of dopamine using brain transplants. Morphological and pharmacological aspects of vasopressin receptor ontogeny in the rat brain are examined. Finally, autoradiographic data on catecholamine receptor localization and characterization in the human hypothalamus, locus coeruleus, and frontal cortex are presented and discussed with reference to their applications in the study of neuropsychiatric disorders such as schizophrenia and senile dementia of the Alzheimer's type.

Pneumococcosuria in children

Streptococcus pneumoniae was present, in pure or mixed culture, in 43 (0.08%) of 53,499 urine cultures submitted from a pediatric population over a 4-year period. Data were analyzed from 28 children, from whom 78% of these positive cultures originated. Ninety-six percent of the children were female, and the median age was 3 years (range, 0.4 to 17 years). Only five children had S. pneumoniae as the sole organism cultured from the urine, and all five had only a single urine culture. Urine from the other 23 children contained other organisms as well. Small numbers of pneumococci were found in most urines: 74% contained less than 10(4) CFU/ml and 93% contained less than 10(5) CFU/ml. There was no association between genitourinary symptoms and pneumococcosuria, and complete resolution of symptoms occurred in both treated and untreated children. Pneumococcosuria could not be explained by pneumococcal bacteremia. We conclude that pediatric pneumococcosuria is not associated with urinary tract infections in children, or with pneumococcal bacteremia or invasive disease elsewhere. Pneumococcosuria probably reflects contamination of urine specimens with S. pneumoniae from perineal colonization.

Site-directed mutagenesis of yeast cytochrome c peroxidase shows histidine 181 is not required for oxidation of ferrocytochrome c

The long-distance electron transfer observed in the complex formed between ferrocytochrome c and compound I, the peroxide-oxidized form of cytochrome c peroxidase (CCP), has been proposed to occur through the participation of His 181 of CCP and Phe 87 of yeast iso-1 cytochrome c [Poulos, T. L., & Kraut, J. (1980) J. Biol. Chem. 255, 10322-10330]. We have examined the role of His 181 of CCP in this process through characterization of a mutant CCP in which His 181 has been replaced by glycine through site-directed mutagenesis. Data from single-crystal X-ray diffraction studies, as well as the visible spectra of the mutant CCP and its 2-equiv oxidation product, compound I, show that at pH 6.0 the protein is not dramatically altered by the His 181----Gly mutation. The rate of peroxide-dependent oxidation of ferrocytochrome c by the mutant CCP is reduced only 2-fold relative to that of the parental CCP, under steady-state conditions. Transient kinetic measurements of the intracomplex electron transfer rate from ferrous cytochrome c to compound I indicate that the rate of electron transfer within the transiently formed complex at high ionic strength (mu = 114 mM, pH = 6) is also reduced by approximately 2-fold in the mutant CCP protein. The relatively minor effect of the loss of the imidazole side chain at position 181 on the kinetics of electron transfer in the CCP-cytochrome c complex precludes an obligatory participation of His 181 in electron transfer from ferrous cytochrome c to compound I.(ABSTRACT TRUNCATED AT 250 WORDS)

Detection of vasopressin messenger RNA in cells within the bed nucleus of the stria terminalis by in situ hybridization histochemistry

In situ hybridization histochemistry and quantitative autoradiography were used to confirm the presence of cells within the bed nucleus of the stria terminalis (BNST) which express the vasopressin (VP) gene and to assess the biosynthetic capacity of these cells throughout the rostrocaudal extent of the nucleus. Brain sections from adult male Wistar rats were hybridized with a 35S-labeled 48-base oligonucleotide probe. Clusters of grains were present over cells in the BNST. Cells were parvocellular in appearance and signal over cells was determined to be specific since it was abolished by RNase pretreatment or incubation with 100-fold excess unlabeled probe. The distribution of VP-mRNA containing cells in the BNST corresponds closely to that previously reported by immunocytochemistry. No clear-cut rostral to caudal gradient was found for gene expression as measured by grains/cell. In situ hybridization techniques can provide a powerful tool to study the regulation of central VP pathways in the BNST.

Accuracy of delivery of cefazolin, chloramphenicol, and vancomycin by a controlled-release membrane infusion device

The effects of flow rate and drug concentration on the accuracy of in vitro delivery of cefazolin, chloramphenicol, and vancomycin by a new controlled-release membrane infusion device, MICROS, were studied. Cefazolin, chloramphenicol, and vancomycin 1 g in sterile water for injection 10 mL were injected into the drug chamber of the device and delivered through an administration set with 0.9% sodium chloride injection from a primary line. Drug delivery was studied at four flow rates (0.5, 1.0, 1.5, and 2.0 mL/min). In addition, three concentrations of each drug (25, 50, and 100 mg/mL for cefazolin and vancomycin, and 50, 100, and 200 mg/mL for chloramphenicol) were studied at a fixed flow rate of 1 mL/min. Samples were collected in triplicate every 2.5-5.0 minutes using a fraction collector over a 90-minute period for cefazolin and a 120-minute period for chloramphenicol and vancomycin. The concentration of each drug was measured by high-performance liquid chromatography. At various flow rates, the time for delivery of greater than or equal to 95% of each dose ranged from 30 to 55 minutes for cefazolin, 45 to 70 minutes for chloramphenicol, and 50 to 65 minutes for vancomycin. At various concentrations, greater than or equal to 95% of each dose was delivered in 40 to 55 minutes for cefazolin, 40 to 70 minutes for chloramphenicol, and 50 to 60 minutes for vancomycin. The desired delivery times were 30-60 minutes for cefazolin and chloramphenicol and 50-70 minutes for vancomycin. Delivery of cefazolin and vancomycin by the MICROS membrane infusion system was accurate. Some delay was encountered in the delivery of chloramphenicol.(ABSTRACT TRUNCATED AT 250 WORDS)

The evolutionary conservation of DNA polymerase alpha

The evolutionary conservation of DNA polymerase alpha was assessed by immunological and molecular genetic approaches. Four anti-human KB cell DNA polymerase alpha monoclonal antibodies were tested for their ability to recognize a phylogenetically broad array of eukaryotic DNA polymerases. While the single non-neutralizing antibody used in this study recognizes higher mammalian (human, simian, canine, and bovine) polymerases only, three neutralizing antibodies exhibit greater, but variable, extents of cross-reactivity among vertebrate species. The most highly cross-reactive antibody recognizes a unique epitope on a 165-180 kDa catalytic polypeptide in cell lysates from several eukaryotic sources, as distant from man as the amphibians. Genomic Southern hybridization studies with the cDNA of the human DNA polymerase alpha catalytic polypeptide identify the existence of many consensus DNA sequences within the DNA polymerase genes of vertebrate, invertebrate, plant and unicellular organisms. These findings illustrate the differential evolutionary conservation of four unique epitopes on DNA polymerase alpha among vertebrates and the conservation of specific genetic sequences, presumably reflective of critical functional domains, in the DNA polymerase genes from a broad diversity of living forms.

Determination of codeine and morphine in human plasma by high performance liquid chromatography with serial electrochemical detection

A method is described for the determination of codeine and its metabolite, morphine, at low nanogram concentrations in plasma. Analysis is accomplished by high-performance liquid chromatography utilizing a cyanopropyl normal bonded phase (NBP) column in reversed-phase mode and two electrochemical detectors in series configuration. Two internal standards are utilized, ethyl morphine for codeine and nalorphine for morphine. Codeine and morphine concentration data are presented for several patients receiving codeine-containing medications. The lower limit of detectability was 2.00 +/- 0.39 ng per mL for codeine and 1.20 +/- 0.83 ng per mL for morphine. The patient sample mean within-run coefficients of variation for codeine and morphine (at 10 ng per mL) were less than 10 percent, n = 30. The between-run coefficient of variation for codeine was also less than 10 percent (over a range of two to 190 ng per mL, n = 61), and was approximately 15 percent for morphine (over a range of two to 40 ng per mL, n = 31).

Clinical disease spectrum and pathogenic factors associated with Plesiomonas shigelloides infections in humans

Plesiomonas shigelloides is a gram-negative, facultatively anaerobic rod whose appropriate taxonomic position is presently under investigation. The isolation and identification of this microorganism in contaminated specimens (e.g., feces) by a clinical laboratory depend on the screening of gram-negative colonies for oxidase and indole positivity and the appropriate use of selective and differential agars. Plesiomonads have been associated with extraintestinal diseases (bacteremia, meningitis) on rare occasions; they have been recovered sporadically from patients presenting with acute gastroenteritis. Although case reports and epidemiologic data support a role for P. shigelloides in diarrheal disease, laboratory investigations have failed to identify an enteropathogenic mechanism in these bacteria consistently or to reveal an animal model that faithfully reproduces the disease. Moreover, studies with volunteers have failed to establish an etiologic relation between Plesiomonas and bacterial gastroenteritis. An accurate picture of the role of this bacterium in human disease must await future studies.

Dose-dependent effects of oral and intravenous glucose on insulin secretion and clearance in normal humans

Insulin secretion and clearance were studied in 2 groups of 7 normal subjects who each received 25, 50, and 100 g of glucose either orally or intravenously (iv) on separate occasions. Insulin secretion rates were calculated during a 1-h base line and for 5 h after glucose administration from a two-compartmental analysis of peripheral C-peptide concentrations using individual kinetic parameters derived after iv bolus injections of biosynthetic human C-peptide. Incremental glucose areas after oral or iv glucose increased as a function of the glucose dose (P = 0.0001). Incremental insulin secretion increased with increasing doses of both oral and iv glucose (P = 0.0001). The metabolic clearance rate (MCR) of endogenous insulin was calculated as the ratio of the total area under the insulin secretion rate curve and the simultaneous peripheral insulin concentration curve. The basal MCR was 1,879.5 +/- 110.5 ml/min (mean +/- SE). The poststimulatory MCR decreased with increasing doses of both oral and iv glucose concomitant with the greater insulin secretory response (P = 0.0014). This decrease in insulin clearance was not significantly different between oral and iv administration of glucose (P = 0.495). In conclusion diminished insulin clearance may be seen after marked stimulation of insulin secretion with larger doses of oral and iv glucose.

Interaction of a vasopressin antagonist with vasopressin receptors in the septum of the rat brain

The ability of d(CH2)5-Tyr(Me)-arginine-8-vasopressin, an antagonist of peripheral pressoric (V1-type) vasopressin receptors, to label vasopressin binding sites in the septum of the rat brain was evaluated. Using crude membrane preparations from the septum, 3H-arginine-8-vasopressin (AVP) specifically labels a single class of binding sites with a Kd of 2.9 nM and maximum binding site concentration of 19.8 fmole/mg protein. 3H-Antag also labels a single class of membrane sites but with higher affinity (Kd = 0.47 nM) and lower capacity (10.1 fmole/mg protein) than 3H-AVP. The rank order of potency of various competitor peptides for 3H-AVP and 3H-Antag binding was similar. Oxytocin was 100-1,000 fold less potent than AVP in competing for binding with both ligands. 3H-AVP and 3H-Antag showed similar labeling patterns when incubated with septal tissue slices. Unlabeled Antag also effectively antagonized vasopressin-stimulated phosphatidylinositol hydrolysis in septal tissue slices.

Dietary lactose improves endochondral growth and bone development and mineralization in rats fed a vitamin D-deficient diet

Lactose promotes the intestinal absorption of calcium independent of the vitamin D endocrine system. The purpose of this study was to determine the effect of lactose supplementation on endochondral bone growth, bone development and mineralization in weanling rats fed a vitamin D-deficient diet. Rat pups were weaned from vitamin D-deficient dams and fed a vitamin D-deficient diet containing sucrose as the primary carbohydrate source or a similar diet but containing 20% lactose. After 4 wk, body weights, serum calcium levels and endochondral bone elongation rates in the lactose-fed animals were higher than in rats fed the sucrose diet. In addition, bone weights, bone calcium content, percent bone ash of bone dry weight, percent metaphyseal osseous tissues and bone osteoid content in the lactose-fed rats were different from those in the rats fed the sucrose diet. In all cases the changes in osseous tissues that were observed in the animals fed the lactose-supplemented diet were toward normal values as observed in age-matched animals fed a vitamin D-replete diet. The improvements in bone growth and development due to lactose supplementation occurred independent of the vitamin D endocrine system and are likely the result of improved calcium absorption in the intestine.

Suicide and suicidology in the Soviet Union

This study was conducted in order to obtain information on suicide in the Soviet Union, an important subject for which we have no scientific literature. Studies of attempted suicide in Soviet psychiatric journals were analyzed. This information was supplemented by interviews with Soviet psychiatrists now living abroad. The results of this inquiry show that suicide is a subject that clearly has become of increasing concern in the Soviet Union. Furthermore, in spite of the absence of essential statistical data on mortality, there is evidence indicating that the rate of Soviet suicide may be rising in certain parts of the country. Finally, growing concern about suicide has led to expanded prevention programs and to a new emphasis on social and psychological etiological explanations. In particular, the role of the Soviet family in crisis has been emphasized as a major influence in understanding the causes of suicidal attempts.

Insulin secretion and clearance. Comparison after oral and intravenous glucose

Insulin secretion and clearance in response to the administration of oral and intravenous glucose was investigated in nine normal men. C-peptide metabolic kinetics were calculated by analysis of individual C-peptide decay curves after the bolus injection of biosynthetic human C-peptide. Glucose was administered to the subjects on three occasions: as a 75-g oral dose, a 75-g i.v. infusion, and an intravenous glucose infusion at a variable rate adjusted to mimic the peripheral glucose levels obtained after the oral glucose load (matching experiment). Glucose, insulin, and C-peptide concentrations were measured for the subsequent 5 h. The glucose level after the oral glucose load (115.9 +/- 2.6 mg/dl, mean +/- SE) closely approximated that after the matching experiment (120.5 +/- 2.5 mg/dl) but was significantly lower than after 75 g i.v. glucose (127.7 +/- 3.4 mg/dl, P less than .05). Analysis of the areas under the peripheral concentration curves (60-360 min) showed that the responses of both insulin (52.7 +/- 5.6 and 46.5 +/- 4.5 pmol.ml-1.300 min-1) and C-peptide (252.7 +/- 27.5 and 267.0 +/- 21.6 pmol.ml-1.300 min-1) were not significantly different after the oral and 75-g i.v. glucose studies, respectively, whereas in the matching experiment, both the insulin (26.1 +/- 3.9 pmol.ml-1.300 min-1) and C-peptide (178.0 +/- 18.9 pmol.ml-1.300 min-1) responses were lower (P less than .05) than in the other two studies. Insulin secretory rates were derived from peripheral C-peptide concentrations with an open two-compartment model and individually derived model parameters. (ABSTRACT TRUNCATED AT 250 WORDS)

Stability of vancomycin hydrochloride in various concentrations of dextrose injection

The stability of vancomycin hydrochloride in plastic syringes containing high concentrations of dextrose injection after storage for 24 hours in a refrigerator followed by storage for two hours at room temperature was studied. Vancomycin hydrochloride was reconstituted with sterile water for injection to a concentration of 50 mg/mL. One-milliliter samples were added to 9 mL of various concentrations of dextrose injection (5, 10, 15, 20, 25, and 30%) in 10-mL plastic syringes. Ten syringes of each concentration were stored at 4 degrees C for 24 hours. At various storage times, samples were assayed in triplicate for vancomycin using high-performance liquid chromatography. After 24 hours, the syringes were removed from the refrigerator, and the vancomycin concentration was determined after storage for two hours at room temperature. Percent change in vancomycin concentration during storage for 24 hours was less than 6% in all cases except for 5% dextrose injection at 4 and 24 hours. Vancomycin concentration did not change (percent change 0.7-5%) during storage for two hours at room temperature. Vancomycin hydrochloride is stable in various concentrations of dextrose injection when stored in plastic syringes for 24 hours in the refrigerator followed by two hours at room temperature.

Attempts to improve tissue survival during ex vivo storage

Ex vivo hypothermic perfusion has been shown to enhance short-term survival of organs before transplantation. The effects of perfusion, control of media pH, and systemic drug treatment were studied utilizing superficial epigastric free flaps in Sprague-Dawley rats. Viability of the flaps could be reliably maintained (9/10, 90%) for 72 hours using simple storage in phosphate-buffered Ringer's (pH 7.8) at 4 degrees C. Pretreatment with prostaglandin E1 was of slight benefit. Flap perfusion with or without pharmacologic agents was not beneficial.

Opioid regulation of luteinizing hormone secretion in the male rat

Current evidence suggests that endogenous opioid peptides (EOPs) tonically inhibit secretion of luteinizing hormone (LH) by modulating the release of gonadotropin-releasing hormone (GnRH). Because of their apparent inhibitory actions, EOPs have been assumed to alter both pulse frequency and amplitude of LH in the rat; and it has been hypothesized that EOP pathways mediate the negative feedback actions of steroids on secretion of GnRH. In order to better delineate the role of EOPs in regulating secretion of LH in the male rat, we assessed the effects of a sustained blockade of opiate receptors by naloxone on pulsatile LH release in four groups: intact male rats, acutely castrated male rats implanted for 20 h with a 30-mm capsule made from Silastic and filled with testosterone, acutely castrated male rats implanted for 20 h with an osmotic minipump dispensing 10 mg morphine/24 h, and male rats castrated approximately 20 h before treatment with naloxone. We hypothesized that if EOPs tonically inhibited pulsatile LH secretion, a sustained blockade of opiate receptors should result in a sustained increase in LH release. We found that treatment with naloxone resulted in an immediate but transient increase in LH levels in intact males compared to controls treated with saline. Even though mean levels of LH increased from 0.15 +/- 0.04 to a high of 0.57 +/- 0.14 ng/ml, no significant difference was observed between the groups in either frequency or amplitude of LH pulses across the 4-h treatment period. The transient increase in LH did result in a 3- to 4-fold elevation in levels of plasma testosterone over baseline. This increase in testosterone appeared to correspond with the waning of the LH response to naloxone. The LH response to naloxone was eliminated in acutely castrated rats implanted with testosterone. Likewise, acutely castrated rats treated with morphine also failed to respond to naloxone with an increase in LH. These observations suggest that chronic morphine and chronic testosterone may act through the same mechanism to modulate secretion of LH, or once shut down, the GnRH pulse-generating system becomes refractory to stimulation by naloxone. In acutely castrated male rats, levels of LH were significantly increased above baseline throughout the period of naloxone treatment; this finding supports the hypothesis that the acute elevation in testosterone acting through mechanism independent of opioid is responsible for the transient response of LH to naloxone in the intact rat.

Characterization of the pathways for phosphatidylethanolamine biosynthesis in Chinese hamster ovary mutant and parental cell lines

A tritium suicide procedure was devised to facilitate the isolation of Chinese hamster ovary cell mutants defective in phosphatidylethanolamine biosynthesis. One mutant with a 20-50% reduction in [3H]ethanolamine incorporation was chosen for further analysis and was shown to have reduced activity of CTP: phosphoethanolamine cytidylyltransferase. Levels of phosphatidylethanolamine and rates of its biosynthesis were compared in the mutant and parent cell lines. Despite the reduced activity of the CDP-ethanolamine pathway in the mutant, levels of phosphatidylethanolamine were the same in mutant and parent cells. Rates of phosphatidylethanolamine synthesis de novo, as measured by incorporation of 32PO4 into phosphatidylethanolamine, were also the same in mutant and parent cells, as was the rate of incorporation of [3H]serine into both phosphatidylserine and phosphatidylethanolamine. After a long term labeling with [3H]serine, the specific radioactivity of phosphatidylserine was the same as that of phosphatidylethanolamine, and there was no difference in the specific radioactivities of the two lipids between mutant and parent cells. These results implicate decarboxylation of phosphatidylserine as the sole route for synthesis of phosphatidylethanolamine under normal culture conditions.

Tobramycin pharmacokinetics in very low birth weight infants

Tobramycin is commonly used at a dose of 2.5 mg kg-1 12h-1, but this regimen often results in trough serum concentrations exceeding 2 mg l-1. Because of limited data in infants weighing less than 1,000 g at birth, we studied eight newborn infants (gestational age 24-30 weeks; postnatal age 3 X 4 days; birth weight 0.60-0.97 kg) at a modified dosing regimen of 2.5 mg kg-1 18 h-1 or 3.0 mg kg-1 24 h-1. Tobramycin peak and trough serum concentrations ranged from 6.0-10.8 (7.8 +/- 1.5) mg l-1 and 1.2-2.4 (1.7 +/- 0.4) mg l-1, respectively. Serum concentration exceeded 2 mg l-1 in seven of eight patients at 12 h and two of eight at 18 h; none had a trough serum concentration above 2 mg l-1 at 24 h. Total body clearance ranged from 0.55 to 0.82 (0.69 +/- 0.10) ml min-1 kg-1; apparent volume of distribution ranged from 0.44 to 0.71 (0.59 +/- 0.10) 1 kg-1; and elimination half-life ranged from 7.7 to 12.6 (9.9 +/- 1.5) h. These data indicate that the modified dosage regimen of 2.5 mg kg-1 18 h-1 or 3.0 mg kg-1 24 h-1 appears to be more acceptable than the current regimen in achieving effective and safe peak and trough serum concentration of tobramycin in newborn infants weighing less than 1 kg at birth.

Changes in bone mineral and bone formation rates during pregnancy and lactation in rats

Changes in bone chemistry, cortical bone morphometry, and periosteal and trabecular bone formation rates were determined during pregnancy and lactation in rats. Data were obtained using chemical, static morphometric, and fluorochrome-based histomorphometric methods in pregnant or lactating animals and compared with age-matched, unmated controls. There were significant increases in bone weight, ash weight, calcium content, and femoral cross-sectional area by late pregnancy and decreases in these same parameters during lactation. There were also decreases in bone mass and increases in surface:volume ratios of trabecular bone during lactation. There were increases in femoral periosteal and endosteal perimeters associated with the reproductive cycle. Bone formation and appositional rates at the periosteal and endosteal surfaces were elevated during pregnancy, particularly evident at midpregnancy. Periosteal bone formation rates declined during lactation, but trabecular bone formation rates increased. These results indicate that during pregnancy there are increases in bone formation rates contributing to the increases in skeletal mass. During lactation in rats, reductions in skeletal mass are accompanied by increases in bone turnover, particularly evident in trabecular bone.

Tobramycin pharmacokinetics in premature identical twins during newborn period

Tobramycin is frequently used in premature infants but little is known about its pharmacokinetics in identical twins during the newborn period. We studied 6 twin infants (gestational age 29-31 weeks; postnatal age 3-4 days; birth weight 1.0-1.3 kg) receiving tobramycin 2.5 mg/kg i.v. over 20 min every 12-18 h. Steady-state peak and trough serum concentrations of tobramycin were in the range of 5.3-8.4 and 1.2-2.0 micrograms/ml, respectively. Total clearance (ClT) ranged from 0.74 to 1.19 ml/min/kg, distribution volume (V) from 0.74 to 0.94 liter/kg, and elimination half-life (t1/2) from 8.2 to 12.8 h. Comparison of data between infants in three identical twin pairs showed that despite a similar infusion method: (a) the time to achieve peak serum concentration ranged from 0.5 to 2.0 h; (b) the peak and trough concentrations normalized for dose varied from 0 to 50%, and (c) the ClT, V and t1/2 varied from 3 to 20%. These data should be considered in therapeutic drug monitoring of tobramycin in premature, identical twins during the newborn period.