Mutational analysis of the sequences at the termini of the Moloney murine leukemia virus DNA required for integration

The insertion of retroviral DNA into the genome of the infected cell to form the integrated provirus requires the presence of short inverted repeat (IR) sequences at the viral DNA termini. To examine the sequence requirements at the IRs for integration of the Moloney murine leukemia virus, we generated a series of mutants with deletion and substitution mutations and tested their ability to replicate and form proviruses in vivo. The experiments did not detect evidence of a requirement for sequences outside the IRs, and only a very loose requirement for the IR sequences, with many point mutations well tolerated. Examination of the mutants suggests that bases very near the terminus and those approximately one turn of the DNA helix away from the terminus are important for recognition by the integrase function.

Vancomycin pharmacokinetics in neonates and infants: a retrospective evaluation

OBJECTIVE

To evaluate the frequency with which current loading and maintenance vancomycin dosages achieve target serum concentrations based on pharmacokinetic parameters obtained after the initial dose. Also, to identify the daily vancomycin dosage necessary to achieve target serum concentrations at steady-state and to determine if any relationships exist between vancomycin pharmacokinetic parameters and various patient characteristics.

SETTING

Neonatal intensive care unit (NICU) at Georgia Baptist Medical Center.

PATIENTS/METHODS

Twenty-three infants with suspected or documented gram-positive infection who received intravenous vancomycin between July 1990 and November 1991 were included in this retrospective analysis. Gestational age range from 23 to 41 weeks and postconceptional age (PCA) at the time of the study ranged from 26 to 46 weeks. Vancomycin therapy was initiated with a loading dose of 15 mg/kg, followed by a maintenance dosage of 20-30 mg/kg/d, which was usually given as 10 mg/kg q8-12h. All vancomycin doses were administered using a syringe pump. Peak and trough serum concentrations were obtained following the first dose. Vancomycin pharmacokinetic parameters were determined using a one-compartment model. Infants receiving indomethacin within two weeks prior to study were analyzed separately (group 2, n = 4). All other infants were included in group 1 (n = 19).

RESULTS

For group 1, vancomycin clearance (Cl), volume of distribution (Vd), and half-life were (mean +/- 1 SD) 0.072 +/- 0.032 L/kg/h, 0.52 +/- 0.08 L/kg, and 5.6 +/- 1.6 hours, respectively. For both groups, loading doses provided 1-hour postinfusion peak concentrations of 25-35 mg/L in one of every two infants studied, whereas only three percent of initial maintenance doses were projected to provide desired peak and trough concentrations at steady-state. For group 1, the mean daily dosage necessary to provide target peak (25-35 mg/L) and trough (5-10 mg/L) concentrations at steady-state was larger than that initially prescribed (29.6 +/- 13.1 vs. 22.2 +/- 4.7 mg/kg/d). For group 2, the mean daily dosage required to achieve target peak and trough concentrations at steady-state was smaller than that initially prescribed (14.8 +/- 4.3 vs. 20.0 +/- 0.1 mg/kg/d) and was exactly half of that required for group 1. Excellent correlations were observed between PCA and vancomycin Cl (L/h) (r = 0.92; p < 0.0001), body weight and Vd(L) (r = 0.94; p < 0.0001), body weight and vancomycin Cl (L/h) (r = 0.85; p < 0.0001), PCA and Vd (L) (r = 0.89; p < 0.0001), and body surface area and Vd (L) (r = 0.93; p < 0.0001) for group 1. Moderate correlations were also noted between PCA and Cl relative to body weight (L/kg/h), postnatal age and Cl (L/kg/h), and PCA and vancomycin dosage requirements (mg/kg/d). No linear correlation was observed between any patient characteristic and Vd standardized for body weight.

CONCLUSIONS

Our data demonstrate the need for a more accurate method of estimating initial vancomycin dosage requirements in this NICU population. Although some of the relationships revealed in this study could be used to determine vancomycin dosage for infants in the range of approximately 30-36 weeks PCA, we hesitate to suggest this approach presently because of the potential limitations of our study design. Further prospective study is needed to confirm these observations. In addition, further study is necessary to describe the time course of the interaction between vancomycin and indomethacin in infants with successful and unsuccessful closure of their patent ductus arteriosus.

Magnesium in the active site of Escherichia coli alkaline phosphatase is important for both structural stabilization and catalysis

Site-specific mutagenesis was used to explore the roles of the side chains of residues Lys-328 and Asp-153 in Escherichia coli alkaline phosphatase. The D153H enzyme exhibits a 3.5-fold decrease in activity at pH 8.0 compared to that of the wild-type enzyme, while a double mutant D153H/K328H exhibits a 16-fold decrease in activity under these conditions. However, the Km values for both enzymes, employing the substrate p-nitrophenyl phosphate, are lower than the value for the wild-type enzyme. The Ki for phosphate, which is pH- and Mg(2+)-dependent, is decreased for the D153H enzyme and increased for the D153H/K328H enzyme. Relative to the wild-type enzyme, both mutant enzymes bind Mg2+ more weakly and undergo a time-dependent activation induced by Mg2+. The half-time of the activation process is independent of the Mg2+ concentration, indicating that the activation most probably involves a conformational change. The pH versus activity profiles of both enzymes are altered relative to that of the wild-type enzyme and exhibit greatly enhanced activity, relative to that of the wild-type enzyme, at high pH values. The pre-steady-state kinetics for the D153H and D153H/K328H enzymes exhibit a transient burst of product formation at pH 8.0, under conditions at which the wild-type enzyme exhibits no transient burst, indicating that at pH 8.0 the hydrolysis of the covalent enzyme-phosphate complex is rate-determining and not the release of phosphate from the noncovalent enzyme-phosphate complex as is observed for the wild-type enzyme. Therefore, these mutations are directly influencing catalysis.(ABSTRACT TRUNCATED AT 250 WORDS)

Use of theophylline in neonates as an aid to ventilator weaning

Respiratory diseases are major causes of morbidity and mortality in premature neonates. Theophylline has been utilized as an adjunct in facilitating ventilator weaning and in the management of apnea with or without bradycardia. Patient characteristics associated with improved outcome from theophylline have not been determined. The purpose of this study was to evaluate parameters associated with improved outcome in neonates with respiratory diseases receiving theophylline. The study population consisted of premature neonates that were studied retrospectively. Criteria for entry into the study were (1) less than 40 weeks gestation, (2) a diagnosis of respiratory distress syndrome (RDS), apnea of prematurity, hyaline membrane disease (HMD), or bronchopulmonary dysplasia (BPD), (3) dependence on intermittent mandatory ventilation, (4) failure to wean from the ventilator 24 h or more before the study, or (5) receiving theophylline. In this study, we found no correlations between time to wean from the ventilator and postnatal age at the time theophylline was initiated, 5-min APGAR score, and final theophylline serum concentration before complete weaning from the ventilator. However, there were significant negative correlations between birthweight and gestational age with respect to time to wean from the ventilator. The average theophylline serum concentration before weaning from the ventilator for this population of neonates was approximately 5-10 micrograms/ml, indicating that theophylline is not beneficial as an aid to ventilator weaning at serum concentrations < 10 micrograms/ml.

Inositol hexakisphosphate receptor identified as the clathrin assembly protein AP-2

To clarify the function of the receptor binding protein for inositol hexakisphosphate (IP6), we obtained a partial amino acid sequence from the purified protein and a partial nucleotide sequence from a cDNA clone of the gene. The sequences are essentially identical to those of the alpha-subunit of the clathrin assembly protein AP-2. The IP6 receptor protein analyzed by SDS-PAGE contains a series of subunits which are the same as those of AP-2. Antibodies to AP-2 react with the IP6 receptor protein in immunoblot analysis.

A mutation at one end of Moloney murine leukemia virus DNA blocks cleavage of both ends by the viral integrase in vivo

The integration of retroviral DNA proceeds through two steps: trimming of the termini to expose new 3' OH ends, and the transfer of those ends to the phosphates of target DNA. We have examined the ability of the Moloney murine leukemia virus integrase protein (IN) to trim the termini of the preintegrative DNA of mutant viruses with alterations in the U3 inverted repeat. The mutant terminus of one replication-defective viral DNA, containing a 7-bp deletion in the U3 inverted repeat, was not trimmed to produce the normal recessed end. Remarkably, the other terminus of this mutant DNA was also not trimmed, even though its sequence is wild type. This finding suggests that the IN protein requires the presence of two good ends before becoming properly activated to trim either one.

Recognition sites for clathrin-associated proteins AP-2 and AP-3 on clathrin triskelia

AP-2 and AP-3 are cellular proteins that drive the in vitro polymerization of clathrin triskelia into cage structures. The interaction of these two types of assembly proteins (APs) with preassembled clathrin cages has been studied in order to identify the sites on the triskelia required for binding. Comparing binding of the APs to intact or to proteolytically clipped cages, we attempted to distinguish between binding to the terminal domain, the globular end of the heavy chain, and binding to the hub of the clathrin triskelia, the portion that remains assembled after trypsin treatment. AP-3 binds to intact clathrin cages but not to those that were treated with trypsin. AP-3 also bound to cages consisting solely of clathrin heavy chains; proteolysis of these cages also eliminated AP-3 binding. In addition, AP-3 did not bind to either isolated hubs or terminal domains that had been immobilized on Sepharose. These data indicate that clathrin light chains are not required for binding of AP-3, and that neither terminal domain nor hubs alone will suffice. However, an intact heavy chain is both necessary and sufficient for the binding of AP-3. Previous work has demonstrated one binding site for AP-2 on proteolyzed cages containing only clathrin hubs; the existence of a second binding site associated with the terminal domain was hypothesized. Here we provide direct evidence for recognition by AP-2 of isolated terminal domains immobilized on Sepharose and show that the core of the AP-2 molecule is responsible for this interaction. These results provide the first demonstration of a functional role for the conserved terminal domain of the clathrin heavy chain.

Effect of education on the appropriateness of serum drug concentration determination

The purpose of this study was to document the effect of education on the appropriateness of serum drug concentration (SDC) collection. This study included a period of education for hospital personnel involved in the acquisition of drug levels. These included nursing staff, lab personnel, house-staff (residents/interns), ward clerks, and pharmacists. This study included patients receiving aminoglycoside and/or vancomycin while on the general medicine service during the specified study periods. Patients receiving less than 72 h of antimicrobial therapy and patients transferred to or from the surgery service were excluded from the study. A retrospective pre- and posteducation comparison using Chi-square analysis was made to determine whether the percentage of appropriate and useful SDCs was improved through education. There was a significant difference (p less than 0.005) between the percentage of appropriate SDCs in the pre- and posteducation period. As a result of the study, a change in procedure for ordering SDCs was initiated, using an educational program, in order to continue the trend of appropriate SDCs at the Veterans Administration.

Effect of monitoring drug concentrations through lines used to administer the drugs: an in vitro study

Elevated drug concentration (DC) can be caused by intentional or iatrogenic overdoses and sampling technique errors. This study examined, in vitro, technique factors that can cause and prevent false elevations of DCs when drugs are administered through the catheter lines from which blood samples are later taken for DC analysis. Digoxin, aminophylline, and phenytoin were administered through central catheters in concentrations simulating those used clinically. Drug solution remained in the lumen for a time similar to that encountered clinically, then either remained in the tubing or was flushed out with 5 ml of normal saline (NS). After 6 h, a 5-ml sample was withdrawn for DC analysis (the tip of the catheter placed in NS, which represented blood supply). Prior to final sample withdrawal, 5 ml of NS was drawn through half of the lines and discarded to simulate methods used to prevent contamination. Thus, various flushing/no flushing and sample discarding/no discarding techniques were analyzed. When diluted concentrations of drug were administered, minor artifactual DCs were observed unless the line was not flushed or sample fluid discarded prior to final sampling. With undiluted drug administration, only flushing after the dose and discarding a sample prior to final sampling prevented artifactual DCs. Clinicians should be aware of the potential for such artifactual elevations of DCs and should encourage techniques that prevent their occurrence.

A statewide survey of pharmacokinetic service provision in Georgia

A survey of pharmacokinetic service (PKS) provision and characteristics of the service was conducted in Georgia's 223 hospitals. The survey's questionnaire, returned by 133 (59.6%) institutions, showed that 23.3% currently had a PKS and that 47% of those without a PKS had plans to establish one in the future. Services were primarily provided by pharmacists (93%) who were certified to provide the consultations in only 40% of the institutions and the PKS was run through either the pharmacy (93%) or pathology laboratory. All services used calculators and/or computers with a variety of software programs to assist in pharmacokinetic evaluations. Patients were charged for the service in 38% of the institutions.

Clathrin assembly protein AP-3. The identity of the 155K protein, AP 180, and NP185 and demonstration of a clathrin binding domain

Three independently isolated clathrin-associated proteins have been reported that have molecular weights of approximately 155,000-185,000 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis: the 155K protein (Keen, J. H., and Black, M. M. (1986) J. Cell Biol. 102, 1325-1333), AP 180 (Ahle, S., and Ungewickell, E. (1986) EMBO J. 5, 3143-3149), and NP185 (Kohtz, D. S., and Puszkin, S. (1988) J. Biol. Chem. 263, 7418-7425). Using two-dimensional isoelectric focusing polyacrylamide gel electrophoresis and one- and two-dimensional immunoblots with two different monoclonal antibodies, we show that these three proteins are identical. The term AP-3 is used to denote this protein. A preliminary analysis of the domain structure of AP-3 was done by controlled proteolysis. Trypsin treatment of AP-3 yields two distinct classes of products. The larger fragments obtained (100,000-135,000 apparent Mr) are acidic and behave anomalously on gel electrophoresis, yielding aberrantly high Mr and exhibiting poor dye binding; these characteristics are shared with intact AP-3. Trypsin also generates a smaller neutral species of approximately 30,000 Da which migrates appropriately on sodium dodecyl sulfate-gel electrophoresis, binds dye comparatively strongly, and behaves as a monomeric globular species in solution. In addition, this species, which is also released by a variety of other proteases, binds specifically and reversibly to clathrin-Sepharose, identifying it as a clathrin recognition domain.

Multidimensional work sampling to quantify a pharmacokinetics resident's duties

A multidimensional work-sampling technique was used to quantify a pharmacokinetics resident's duties. Four dimensions were measured: activity, contact, function, and location. A code list of 47 variables was developed to encompass all activities of the resident being observed. A combination of self-reporting and observer reporting was used to test the veracity of the resident's report and to determine whether differences in reporting occurred. Observation was done 20 times a day over a five-week period (24 working days). Random time periods separated the observation points. The observer and the resident recorded 260 and 220 observations, respectively, for a total of 480. The overall reliability measure was 78%, indicating good interobserver agreement. The resident spent about 36% of his time doing work related to pharmacokinetics consultations and 23% of his time attending meetings. He spent a large proportion of time (48.5%) working alone. Much of his remaining time was spent with the Pharm.D. students and the preceptors. Multidimensional work sampling based on a combination of self-reporting and observer reporting is a useful tool for quantifying the work practices of pharmacokinetics residents.

A comparison of venous versus capillary measurements of drug concentration

Accessing patient's veins for drug level sampling is not always feasible. The use of capillary sampling techniques is often utilized when venous access is hampered. In the therapeutic monitoring of patients, unexpected drug level results often occur that can be caused by a number of different factors. The possibility that differences in assay results might occur if samples were collected by capillary stick vs. venous phlebotomy was examined by simultaneous sampling in 18 patients. Although correlation was very high (0.999) and percentage differences fairly low (range of 0 to 15.4%), a statistical difference was noted in the sampling methods. The precision was 6.5 +/- 6.58% and there was a slight negative bias (-3.76%), with capillary samples less than venous samples. Although there were statistical differences for the drugs studied in the concentration ranges evaluated, capillary samples should provide fairly small errors when compared to venous samples.

Effect of cimetidine on oral digoxin absorption

Cimetidine is a commonly prescribed histamine 2-receptor antagonist used in the treatment of gastric acid-related disorders. Cimetidine can interact with a number of drugs, including theophylline, benzodiazepine sedative hypnotics, warfarin, and antiarrhythmics. Problems may occur in patients receiving drugs with a narrow therapeutic index when combined with cimetidine. Contrasting reports have been published on the potential interaction between digoxin and cimetidine. This study focuses on cimetidine's effect on the pharmacokinetic disposition of chronic digoxin usage. Six hospitalized patients with stable congestive heart failure received their usual maintenance dose of digoxin 0.125-0.25 mg/d po. After confirming steady-state digoxin concentrations, cimetidine 300 mg po q6h was administered. Two patients were dropped from the study. Analysis of digoxin serum concentrations, area under the curve, and the rate of elimination suggested no significant differences in digoxin parameters when combined with cimetidine.

Implementing and maintaining a private pharmacokinetics practice

The development and maintenance of a private-practice pharmacokinetics service is described. A contracted pharmacokinetics service has been in place at Georgia Baptist Medical Center, a 525-bed hospital, for the past eight years. Physician support, inhouse study results, and literature documentation of the benefits of scheduling drug concentration determinations were used to convince hospital administrators of the value of a pharmacokinetics service. Services were reimbursed by increasing the fee charged for each drug concentration determination, with payment made to the pharmacokinetics service on a monthly basis. The service is associated with the pathology department for administrative purposes. Each member of the pharmacokinetics service is credentialed by the medical staff. The group trains part-time personnel to provide services when needed. Services provided by the group but not required by the contract include collecting quality assurance data, conducting research, serving on hospital committees, writing newsletter articles, conducting inservice-education programs, and providing clinical interventions for nonconsultation patients. This private-practice pharmacokinetics service provides high-quality services and is well accepted within the institution.

Falsely elevated digoxin levels: another look

Digoxin therapy can cause important toxic events when elevated drug levels occur. Interpreting drug levels can be hampered by artifactual errors such as poor assay quality, incorrect timing or drawing of blood samples, and, as has been demonstrated for tobramycin, errors due to drawing blood through drug administration catheters. A case is reported in which a correctly timed and analyzed digoxin level of 33.60 ng/ml may have been due to drawing the blood sample through a line used to administer digoxin eight hours earlier. Subsequent measurements by venipuncture documented much lower concentrations.

Seven years of experience with a pharmacokinetic service

There have been several reports describing the impact of pharmacokinetic services on cost containment. The purposes of this report are to describe seven years of experience with the operation of a pharmacokinetic service, and the processes used to implement and maintain the service along with a discussion of the impact of the service on hospital cost and patient charge containment. The major functions of the pharmacokinetic service are to; 1) provide clinical pharmacokinetic and pharmacology consultation upon physician request, 2) coordinate the scheduling of serum drug levels (SDLs), and 3) provide quality assurance and utilization review reports related to the service. Data gathered from the service are reported to the medical staff monthly and are incorporated into the hospital's on-going drug usage evaluation. The results of continuous review demonstrate that direct intervention of a pharmacokineticist and a systematic approach to drug level scheduling yielded less than 1% of inappropriately collected SDLs, and in the latest year, a yearly patient charge savings of +116,304. In another study evaluating the service, it was demonstrated that when aminoglycoside dosages are adjusted by a pharmacokineticist, a patient charge savings of +491 per patient is realized. This review of seven years of experience with a pharmacokinetic service supports the conclusion that these services can have a beneficial impact on hospital costs. Furthermore, data gathered from the service can be utilized for the hospital's overall quality assurance program.