Na+/K(+)-ATPase: modes of inhibition by Mg2+

Adding 15 mM free Mg2+ decreased Vmax of the Na+/K(+)-ATPase reaction. Mg2+ also decreased the K0.5 for K+ activation, as a mixed inhibitor, but the increased inhibition at higher K+ concentrations diminished as the Na+ concentration was raised. Inhibition was greater with Rb+ but less with Li+ when these cations substituted for K+ at pH 7.5, while at pH 8.5 inhibition was generally less and essentially the same with all three cations: implying an association between inhibition and ion occlusion. On the other hand, Mg2+ increased the K0.5 for Na(+)-activation of the Na+/K(+)-ATPase and Na(+)-ATPase reactions, as a mixed inhibitor. Changing incubation pH or temperature, or adding dimethylsulfoxide affected inhibition by Mg2+ and K0.5 for Na+ diversely. Presteady-state kinetic studies on enzyme phosphorylation, however, showed competition between Mg2+ and Na+. In the K(+)-phosphatase reaction catalyzed by this enzyme Mg2+ was a (near) competitor toward K+. Adding Na+ with K+ inhibited phosphatase activity, but under these conditions 15 mM Mg2+ stimulated rather than inhibited; still higher Mg2+ concentrations then inhibited with K+ plus Na+. Similar stimulation and inhibition occurred when Mn2+ was substituted for Mg2+, although the concentrations required were an order of magnitude less. In all these experiments no ionic substitutions were made to maintain ionic strength, since alternative cations, such as choline, produced various specific effects themselves. Kinetic analyses, in terms of product inhibition by Mg2+, require Mg2+ release at multiple steps. The data are accommodated by a scheme for the Na+/K(+)-ATPase with three alternative points for release: before MgATP binding, before K+ release and before Na+ binding. The latter alternatives necessitate two Mg2+ ions bound simultaneously to the enzyme, presumably to divalent cation-sites associated with the phosphate and the nucleotide domains of the active site.

Effect of phosphatidylcholine on ultrafiltration in patients on continuous ambulatory peritoneal dialysis

Oral phosphatidylcholine at 900 mg/day was given to 4 patients with high lymph absorption for 8 weeks. Fluid and solute transfer before and after treatment were compared to 4 similar controls given placebo. None of the patients had overt ultrafiltration problems. After treatment, overnight peritoneal effluent phospholipid content did not change significantly. Ultrafiltration as well as solute and glucose transfer remained unchanged at the end of 8 weeks. A controlled trial on patients with overt ultrafiltration problems for a longer duration is required to further elucidate the role of phosphatidylcholine supplementation in patients on continuous ambulatory peritoneal dialysis.

A stepless needle-dilator for expedient percutaneous catheterization: technical note

A new stepless needle-dilator is described which allows arterial puncture and dilation in a single step using a single wall puncture technique. The new needle-dilator causes significantly less arterial damage than a conventional dilator (p less than 0.05). Additionally, time and cost savings are realized by clinical users.

Interventional magnetic resonance imaging in the head and neck

Interventional MRI is clearly in its early stages of development. While the value of MR-guided aspiration cytology and MR evaluation of deep electrode implantation in the brain has already been confirmed with human clinical studies, the future of MR-guided interstitial laser therapy remains to be proven. Despite this, as we look ahead into the 1990s and the millennium, it is possible to imagine dedicated MR laser therapy units for combined radiological and surgical outpatient approaches in what may become the operating rooms of the 21st century.

Interstitial laser phototherapy assisted by magnetic resonance imaging: a new technique for monitoring laser-tissue interaction

The rapid technological advances of magnetic resonance imaging, laser fiberoptics, and compatible probes may allow treatment of deep and sometimes surgically unreachable tumors of the head and neck with minimal morbidity through interstitial laser phototherapy. In this study, a new application of magnetic resonance imaging was developed to monitor and quantify laser-induced tissue damages. Pig skin was exposed to increased levels of argon laser (514.5 nm) at energy densities between 62.5 and 375 J/cm2 as determined by an accurate and reproducible method of dosimetry. Thermal profiles were recorded using an infrared sensor and T1- and T2-weighted magnetic resonance images were taken; afterward, biopsies were performed to quantitate the level of tissue damage. Our results demonstrate that above a certain threshold of laser energy, the magnetic resonance imaging findings are temperature dependent. Appropriate development of a scale matching laser energies, temperature profiles, T1- and T2-weighted magnetic resonance images, and histological quantitation of tissue destruction will allow us to optimize the three-dimensional control and monitoring of laser-tissue interactions.

Differential effects of substrates on three transport modes of the Na+/K(+)-ATPase

With a purified Na+/K(+)-ATPase preparation reconstituted into phospholipid vesicles, Na+/K+, Na+/Na+, and uncoupled Na+ transport were studied using three nucleotides and five substrates of the K(+)-phosphatase reaction that this enzyme also catalyzes. For Na+/K+ exchange, CTP was half as effective as ATP and GTP one-twentieth; of the phosphatase substrates only carbamyl phosphate and 3-O-methylfluorescein phosphate produced significant transport and at merely 1% of the rate with ATP. For Na+/Na+ exchange, comparable rates of transport were produced by ATP, CTP, carbamyl phosphate and acetyl phosphate, although the actual rate of transport with ATP was only 2.4% of that for Na+/K+ exchange; slower rates occurred with GTP (69%), 3-O-methylfluorescein phosphate (51%), and nitrophenyl phosphate (33%). Only umbelliferone phosphate was ineffective. For uncoupled Na+ transport results similar to those for Na+/Na+ exchange were obtained, but the actual rate of transport was still slower, 1.4% of that for Na+/K+ exchange. Thus, not only nucleotides but a variety of phosphatase substrates (which are phosphoric acid mixed anhydrides) can phosphorylate the enzyme at the high-affinity substrate site to form the E1P intermediate of the reaction sequence. Oligomycin inhibited Na+/K+ exchange with ATP by half, but with carbamyl phosphate not at all; with CTP the inhibition was intermediate, one-fourth. By contrast, oligomycin inhibited Na+/Na+ exchange by one-fifth with all three substrates. A quantitative, steady-state kinetic model accounts for the relative magnitudes of Na+/K+ and Na+/Na+ exchanges with ATP, CTP, and carbamyl phosphate as substrates, as well as the extents of inhibition by oligomycin. The model requires that even when Na+ substitutes for K+ a slow step in the reaction sequence is the E2 to E1 conformational transition.

The biocompatibility of compressed collagen foam plugs

The tissue reaction to reexpanded, purified bovine collagen sponge placed percutaneously into the lung, pleural space, liver, kidney, and muscle was studied in dogs and rabbits. In addition, the biocompatibility and radiopacity of tantalum-treated collagen foam plugs was examined. No adverse effects were found. We believe that collagen plugs may be of use in occluding needle tracts from biopsy sites to prevent complications such as bleeding or pneumothoraces.

Pharmacokinetics of amikacin in critically ill neonatal foals treated for presumed or confirmed sepsis

Fourteen foals less than four days of age were treated with the aminoglycoside, amikacin sulphate, and either penicillin or ampicillin for septicaemia, pneumonia, and/or failure of passive immunoglobulin transfer. Serum amikacin concentrations were determined at three times during an 8 or 12 h dosing interval. A 7.0 mg/kg bodyweight dose of amikacin every 8 h was appropriate. Prematurity did not influence mortality. All seven premature foals survived, whereas four of the seven full term foals died. Uraemia in three foals was caused by urinary bladder rupture; amikacin-induced nephrotoxicity was not recognised by clinical chemistries (elevations in serum creatinine or blood urea nitrogen concentrations) or post-mortem findings.

Modification of ligand binding to the Na+/K+-activated ATPase

Interactions between the ligands Mg2+, K+, and substrate and the Na+/K+-activated ATPase were examined in terms of a rapid-equilibrium, random-order, terreactant kinetic scheme for the K+-nitrophenyl phosphatase reaction that is catalyzed by this enzyme. At 37 degrees C and pH 7.5 the derived values for the dissociation constants from the free enzyme were 0.2, 0.08, and 1.4 mM for Mg2+, K+, and substrate, respectively. For Mg2+ interactions, the presence of 20% (v/v) dimethyl sulfoxide (Me2SO) increased the calculated affinity 25-fold; higher concentrations increased affinity still further. Neither reducing the temperature to 20 degrees C nor altering the pH from 6.5 to 8.3 appreciably changed the affinity for Mg2+ in the absence or presence of Me2SO. The Mg2+ sites are thus characterized by an absence of functional groups ionizable in the pH range 6.5-8.3, with binding driven by entropy changes, and with Me2SO, probably through solvation effects on the protein, increasing affinity for Mg2+ close to that for Ca2+ and Mn2+. By contrast, for K+ interactions, the presence of 20% Me2SO increased the calculated affinity only by half; moreover, reducing the temperature to 20 degrees C and the pH to 6.5 both increased affinity and diminished the response to Me2SO. The K+ sites are thus characterized by a marked sensitivity to pH and temperature, presumably through alterations in enzyme conformational equilibria that in turn are modifiable by Me2SO. Inhibition by higher concentrations of Mg2+, which varies inversely with the K+ concentration, was decreased by Me2SO. Finally, for substrate interactions, the presence of 20% Me2SO increased the calculated affinity 4-fold, and, as for Mg2+-binding, neither reducing the temperature nor varying the pH over the range 6.5-8.3 appreciably altered the affinity in the absence or presence of Me2SO. Thus, the substrate sites, like the Mg2+ sites, are characterized by an absence of functional groups ionizable in this range, with binding driven by entropy changes, and with Me2SO increasing affinity for substrate, in this case probably through favoring the partitioning of substrate from the medium into the hydrophobic active site.

Extracranial lesions of the head and neck: preliminary experience with Gd-DTPA-enhanced MR imaging

The authors report initial experience with magnetic resonance imaging enhanced with gadolinium diethylenetriaminepentaacetic acid (DTPA) in 27 patients with various extracranial lesions of the head and neck. Unenhanced T1- and T2-weighted images were compared with T1-weighted images obtained 3-30 minutes after Gd-DTPA administration. Overall, compared with precontrast T1- and T2-weighted images, Gd-DTPA improved the visibility of lesions in 11 and five of 27 patients, respectively. Gd-DTPA particularly improved the conspicuity of tumors of the nasal cavity and paranasal sinuses and tumors having perineural or intracranial extension. Gd-DTPA-enhanced images were equivalent to precontrast T1- and T2-weighted images in five and 13 patients, respectively, and inferior to them in nine and eight patients, respectively. Mixed results were obtained in two patients and one patient when Gd-DTPA-enhanced images were compared with T1- and T2-weighted images, respectively. The authors conclude that Gd-DTPA has definite but limited uses in extracranial head and neck pathologic conditions and that more research is needed to evaluate particular applications.

Pasteurella multocida corneal ulcer following a baseball injury

Pasteurella multocida is an ubiquitous organism that can be isolated from a variety of animals and birds. It is an infrequent ocular pathogen but can cause infection as a result of injury or animal exposure. This article reports a case of P multocida corneal ulcer following a baseball injury.

Solvent effects on substrate and phosphate interactions with the (Na+ + K+)-ATPase

(Na+ + K+)-ATPase activity of a dog kidney enzyme preparation was markedly inhibited by 10-30% (v/v) dimethyl sulfoxide (Me2SO) and ethylene glycol (Et(OH)2); moreover, Me2SO produced a pattern of uncompetitive inhibition toward ATP. However, K+-nitrophenylphosphatase activity was stimulated by 10-20% Me2SO and Et(OH)2 but was inhibited by 30-50%. Me2SO decreased the Km for this substrate but had little effect on the Vmax below 30% (at which concentration Vmax was then reduced). Me2SO also reduced the Ki for Pi and acetyl phosphate as competitors toward nitrophenyl phosphate but increased the Ki for ATP, CTP and 2-O-methylfluorescein phosphate as competitors. Me2SO inhibited K+-acetylphosphatase activity, although it also reduced the Km for that substrate. Finally, Me2SO increased the rate of enzyme inactivation by fluoride and beryllium. These observations are interpreted in terms of the E1P to E2P transition of the reaction sequence being associated with an increased hydrophobicity of the active site, and of Me2SO mimicking such effects by decreasing water activity: (i) primarily to stabilize the covalent E2P intermediate, through differential solvation of reactants and products, and thereby inhibiting the (Na+ + K+)-ATPase reaction and acting as a dead-end inhibitor to produce the pattern of uncompetitive inhibition; inhibiting the K+-acetylphosphatase reaction that also passes through an E2P intermediate; but not inhibiting (at lower Me2SO concentrations) the K+-nitrophenylphosphatase reaction that does not pass through such an intermediate; and (ii) secondarily to favor partitioning of Pi and non-nucleotide phosphates into the hydrophobic active site, thereby decreasing the Km for nitrophenyl phosphate and acetyl phosphate, the Ki for Pi and acetyl phosphate in the K+-nitrophenylphosphatase reaction, accelerating inactivation by fluoride and beryllium acting as phosphate analogs, and, at higher concentrations, inhibiting the K+-nitrophenylphosphatase reaction by stabilizing the non-covalent E2.P intermediate of that reaction. In addition, Me2SO may decrease binding at the adenine pocket of the low-affinity substrate site, represented as an increased Ki for ATP, CTP and 3-O-methylfluorescein phosphate.

Atheroablation with the Kensey catheter: a pathologic study

The mode of action of the Kensey catheter, a new atheroablation device, was investigated. Fresh above-the-knee amputated legs were used for recanalization of the superficial femoral artery. The variables used were identical to those of clinical trials, including a rotational speed of 50,000 rpm and an injection rate of 40 mL/min. The debris produced by the catheter was studied cytologically, and the arterial segments were examined histologically. The particle size in the debris ranged from 1 to 2,000 microns. The softer plaques produced a fine fibrin dust background with long strips of intima ranging from 10 to 2,000 microns. Complicated calcified plaques produced larger background material (10-120 microns) but smaller strips of intima (50-800 microns). Dissections and perforations occurred. Some of the debris produced by the atheroablation process was used to embolize a canine heart and kidney. Small focal infarctions were found in the heart, and large and multiple infarcts were seen in the kidney. In clinical studies the debris appears to be tolerated in the lower extremities. Its safety in the kidney and heart are questioned.

In vitro evaluation of caval filters

This experiment demonstrated the clottrapping ability of two commercially available filters, the Mobin-Uddin and Greenfield, and three experimental filters developed by Amplatz, Günther, and Gianturco. Each filter was tested in a polyethylene tube simulating the inferior vena cava. Separate series of 10 clots, each 3 cm long and 6 mm or 9.2 mm in diameter, were exposed to the test filter. The Mobin-Uddin and Amplatz filters failed by overload: acutely elevated pressures forced clots outside the skirt of the former, and between the limbs of the latter. The Günther filter trapped all incident clots, but migrated downstream when occluded by clot. The Greenfield filter passed clots at normal pressures between its widely spaced legs. The Gianturco (bird's nest) passed clots at normal pressures as well. While filters performed suboptimally, strengthening the anchoring struts of the Günther filter would result in a secure, effective filter.

Hyperglycemia is a stress response in acute stroke

To explore further the relation between admission glucose concentration and outcome in stroke, we measured glucose, fructosamine, and glycosylated hemoglobin concentrations on admission in 216 patients seen within 24 hours after the onset of their first stroke. Fructosamine concentration reflects the degree of glycemia in the preceding 4-6 weeks and glycosylated hemoglobin concentration reflects that in the preceding 3 months. Based on clinical, computed tomographic, and necropsy findings, strokes were classified as cortical infarction, lacunar infarction, or intracerebral hemorrhage. Analyses were done including and excluding 47 diabetic patients. No correlation between neurologic outcome as mortality and fructosamine or glycosylated hemoglobin concentration was found. Survival showed a significant correlation with admission glucose concentration only for patients with intracerebral hemorrhage. Our results suggest that hyperglycemia is unlikely to worsen the outcome of acute stroke and that hyperglycemia probably represents either a latent diabetic state or a stress response.

Characteristics of 3-O-methylfluorescein phosphate hydrolysis by the (Na+ + K+)-ATPase

With 3-O-methylfluorescein phosphate (3-OMFP) as substrate for the phosphatase reaction catalyzed by the (Na+ + K+)-ATPase, a number of properties of that reaction differ from those with the common substrate p-nitrophenyl phosphate (NPP): the Km is 2 orders of magnitude less and the Vmax is two times greater, and dimethyl sulfoxide (Me2SO) inhibits rather than stimulates. In addition, reducing the incubation pH decreases both the Km and Vmax for K+-activated 3-OMFP hydrolysis as well as the K0.5 for K+ activation. However, reducing the incubation pH increases inhibition by Pi and the Vmax for 3-OMFP hydrolysis in the absence of K+. When choline chloride is varied reciprocally with NaCl to maintain the ionic strength constant, NaCl inhibits K+-activated 3-OMFP hydrolysis modestly with 10 mM KCl, but stimulates (in the range 5-30 mM NaCl) with suboptimal (0.35 mM) KCl. In the absence of K+, however, NaCl stimulates increasingly over the range 5-100 mM when the ionic strength is held constant. These observations are interpreted in terms of (a) differential effects of the ligands on enzyme conformations; (b) alternative reaction pathways in the absence of Na+, with a faster, phosphorylating pathway more readily available to 3-OMFP than to NPP; and (c) a (Na+ + K+)-phosphatase pathway, most apparent at suboptimal K+ concentrations, that is also more readily available to 3-OMFP.

Identification of some abnormal haemoglobins by fast atom bombardment mass spectrometry and fast atom bombardment tandem mass spectrometry

The characterization of two abnormal human haemoglobins by fast atom bombardment (FAB) mapping is presented. The first variant, called 'R', exhibits a tryptic FAB map identical to that of normal haemoglobin. However, using Staphylococcus protease V8, a peptide containing the carboxyl end of the beta-chain exhibits a mass shift down to 300 mass units. This clearly indicates the deletion of the two last amino acids of the beta-chain. The second variant, called 'Grenoble', is due to two different modifications of the beta-chain. The location of the Pro----Ser exchange on peptide T5 is achieved by the collisionally activated dissociation mass analyzed ion kinetic energy spectra of the corresponding [MH]+ ion. The m/z value of that peptide indicated a supplementary acid----amide modification, which was located by amino acid sequencing using chemical methods. This work concludes with the necessity of using complementary methods for achieving rapid determinations of abnormal proteins with minute amounts.

Phenytoin dosing in obese patients: two case reports

Phenytoin is used extensively in the treatment of various forms of epilepsy, and remains the drug of choice in partial and generalized tonic-clonic seizures. Because it demonstrates saturable, Michaelis-Menten pharmacokinetics, dosing of phenytoin within the therapeutic range can be very challenging, especially so in obese patients. We present case reports of two obese patients each requiring very large doses of phenytoin sodium (1000 mg/d) to sustain therapeutic serum concentrations and seizure control. There are very few reports in the literature regarding phenytoin pharmacokinetic changes in the obese. We can only theorize possible changes in these parameters. Further investigation in the form of controlled research trials need to be performed before final dosage recommendations can be given.

Substrate sites of the (Na+ + K+)-ATPase: pertinence of the adenine and fluorescein binding sites

The (Na+ + K+)-activated ATPase catalyzes the K+-activated hydrolysis of 3-O-methylfluorescein phosphate (3OMFP) with a Km of 50 microM, nearly two orders of magnitude lower than the Km for nitrophenyl phosphate, 3 mM. Both ATP and nitrophenyl phosphate are competitors toward 3OMFP with Ki values corresponding to their Km values (for ATP that at the low-affinity sites of the E2 conformation). Enzyme treated with fluorescein isothiocyanate (FITC) such that 60% of the (Na+ + K+)-ATPase activity is lost still hydrolyzes both 3OMFP and nitrophenyl phosphate: the apparent Km values are increased less than 2-fold and the Vmax is unaffected. ATP still inhibits these K+-phosphatase reactions of the FITC-treated enzyme, and this inhibition can exceed the 40% of residual (Na+ + K+)-ATPase activity. Evaluation of a kinetic model indicates that the Ki for ATP is increased about an order of magnitude by FITC-binding. Similar results obtain with trinitrophenyl-ATP (TNP-ATP) as inhibitor, in this case with Ki values in the micromolar range. Finally, FITC treatment increases K+-activated ADPase activity. These observations are interpreted as the fluorescein ring of 3OMFP binding to the adenine pocket of the substrate site, thereby conferring high affinity, just as the fluorescein ring of FITC binding to the adenine pocket in the E1 conformation permits specific linkage of the isothiocyanate chain to a particular lysine, Lys-501. Then, coincident with the transition to the E2 conformation, which bears the low-affinity site for ATP and which catalyzes the K+-phosphatase reaction, the FITC molecule tethered to Lys-501 is pulled from the adenine pocket: allowing 3OMFP and ADP to bind as substrates and ATP and TNP-ATP as inhibitors, albeit in altered conformation. The E1 to E2 transition thus involves not only a change from high to low affinity for ATP, but also a distortion of the adenine pocket and the orientation between Lys-501 and Asp-369, the residue associated with catalysis.

Effect of new Vacutainer blood collection tubes on plasma lidocaine concentrations

This study was designed to establish whether plasma lidocaine concentrations changed subsequent to contact with a new formulation of rubber-stopper Vacutainer collection tubes. Plasma lidocaine concentrations from blood samples exposed to rubber stoppers for one hour were compared with concentrations from blood samples which were not exposed to rubber stoppers. Plasma lidocaine concentrations remained essentially unchanged following one-hour exposure to Vacutainer rubber stoppers. The new formulation of "red-top" Vacutainer may be used reliably in lidocaine therapeutic drug monitoring.

A new torque guide wire

A new guide wire that provides markedly improved torque control is described. It was compared with a conventional guide wire in two models, one simulating a drainage tube with numerous side holes and one, the biliary tree. The new wire was much more easily controlled than the conventional guide wire and passed through both models significantly faster (P less than .01 and P less than .005). Although some deterioration in control was noted when it was inserted through a catheter in vivo, the new torque-control wire still exhibited a definite improvement over conventional wires in directional control.

Serum phenobarbital concentration predictions by a personal computer software system

The ability of a personal computer software system to predict actual serum phenobarbital concentrations (SPC) in outpatients taking phenobarbital chronically was assessed by comparing actual with predicted SPC for accuracy, bias, and precision. Data for a four-year period were collected on patients at an outpatient clinic's pharmacokinetic consultation service. The study group included 50 adults and children with at least one SPC taken at a known time after dose administration. Input variables were weight, sex, height, age, concomitant drugs and diseases, phenobarbital dosage regimen, and the time and reported value of all SPC. Initially, SIMKIN (SIMulated KINetics) simulated dosing regimens on the basis of literature estimates of pharmacokinetic parameters; SPC were then estimated for these regimens and compared with actual values. One or two additional SPC were added to the input data and analyzed, and the predicted SPC compared with actual values. Although SIMKIN's accuracy and bias as measured by regression analysis and mean prediction error, respectively, were within clinically acceptable limits, the precision was not. However, these results are limited by the population studied. Patient compliance, concomitant phenytoin therapy, changes in phenobarbital pharmacokinetic parameters with chronic dosing, and disease interactions may significantly affect predictive ability. The clinical effects of these factors need to be evaluated to further improve predictions.

Pharmacokinetics of loprazolam and its principal metabolite in young subjects and elderly hospital patients

1. The pharmacokinetics of loprazolam and its principal pharmacologically active metabolite, the piperazine N-oxide, were compared in young subjects (aged 21-25 years) and elderly patients (aged 63-86 years) following single oral evening doses (0.5 mg and 1 mg). 2. Plasma loprazolam was assayed by a specific h.p.l.c./g.c. method. The N-oxide metabolite was assayed by gas chromography. 3. Mean times to peak plasma concentration of loprazolam did not differ significantly between young and elderly subjects and ranged from 1.6-2.7 h. There was, however, a longer mean time to peak concentration of the N-oxide metabolite in the elderly but this was only statistically different after the 0.5 mg dose (4.5 mg young, 6.4 h elderly). 4. Mean peak plasma concentrations of loprazolam did not differ significantly between young and elderly nor did plasma concentrations of the N-oxide metabolite. 5. Although the mean elimination half-life of loprazolam was not statistically significantly different between young and elderly subjects (range 10.9-16.0 h) there was a trend towards somewhat longer half-lives in the elderly. Furthermore, there was a small but significant increase in the half-life of the N-oxide metabolite in the elderly after the 1 mg dose from 11.7 h to 16.7 h. 6. The areas under the plasma concentration time curves for both loprazolam and its N-oxide were greater in the elderly being some 50-68% (mean 132.0 and 111.5 ng/ml h) above those found in young subjects (mean 89.8 and 66.0 ng/ml h).(ABSTRACT TRUNCATED AT 250 WORDS)

Modified sheath introducer for reduced arterial damage

An introducer-sheath dilator is described, which was modified to protect the leading lip of the sheath during insertion, thus reducing arterial damage. The new sheath and a standard sheath were inserted into the femoral arteries of six dogs. Subsequent histologic examination of the arteries proved the new sheath to be both safe and effective.

Pharmacokinetic monitoring in the community health-care setting

Ambulatory care pharmacokinetic profiling has been utilized with increasing frequency over the last decade. The demonstration of need is the first step in initiating outpatient pharmacokinetic service. This article identifies methods used in demonstrating a need and discusses the normal daily activities of an ambulatory pharmacokinetic service located in a university-based family medicine clinic. The reader will also learn of trends that ambulatory care pharmacokinetic programs will become involved with in the near future.

Buffer, pH, and ionic strength effects on the (Na+ + K+)-ATPase

A dog kidney (Na+ + K+)-ATPase preparation also catalyzes K+-independent and K+-activated phosphatase reactions with p-nitrophenyl phosphate as substrate. K+-independent activity increases with declining pH over the range 7.5 to 5.8, whereas the other two activities decrease. The increased K+-independent activity is similar with imidazole, histidine, and several Good buffers, and is thus attributable to free H+, probably by affecting enzyme conformations rather than by changing affinity for Mg2+ or substrate or by H+ occupying specific K+-sites. The decrease in K+-phosphatase and (Na+ + K+)-ATPase activities with pH also occurs similarly with those buffers, and is not due to changes in apparent affinity for substrate or for cation activators. However, the Good buffers Pipes and ADA inhibit the K+-independent phosphatase reaction strongly, the K+-activated reaction moderately, and the (Na+ + K+)-ATPase reaction little; both contain two acidic groups, unlike the other buffers tested. Inhibition of the phosphatase reaction by Pipes is associated with a decreased apparent affinity for K+ and an increased sensitivity to inhibition by Na+ and ADP, consistent with Pipes hindering conformational transitions to the E2 enzyme forms required for phosphatase hydrolytic activity.

New heavy-duty exchange guide wire

A major drawback of currently used exchange guide wires is insufficient stiffness, causing them to buckle or dislodge when used during catheter exchanges. A new heavy-duty exchange guide wire is described that facilitates catheter exchanges around sharp corners, such as those encountered during various cardiac interventional procedures. The wire was successfully used in experimental valvuloplasty and experimental dilation of the ductus arteriosus.

Effect of thioridazine on phenytoin serum concentration: a retrospective study

Serum phenytoin concentrations before and after the addition of thioridazine were retrospectively compared in 27 adults to determine if an interaction occurred between these two drugs. A change in the serum phenytoin concentration of +/- 4 micrograms/ml was considered clinically significant; by this definition four patients (14.8 percent) had an increase, two (7.4 percent) had a decrease, and most (77.8 percent) demonstrated no change. The mean difference was 0.8 microgram/ml +/- 3.7 micrograms/ml and was not found to be statistically significant (p less than 0.1). Clinically important alterations in phenytoin serum concentration as caused by thioridazine appear to be infrequent.

Fluoride and beryllium interact with the (Na + K)-dependent ATPase as analogs of phosphate

Fluoride irreversibly inhibits the (Na + K)-ATPase, and this inactivation requires divalent cations (Mg2+, Mn2+, or Ca2+), is augmented by K+, but is diminished by Na+ and by ATP. Prior incubation with the aluminum chelator deferoxamine markedly slows inactivation, whereas adding 1 microM AlCl3 speeds it, consistent with AlF-4 being the active species. Prior incubation of the enzyme with vanadate also blocks inactivation by fluoride added subsequently. Fluoride stimulates ouabain binding to the enzyme, and thus the analogy between AlF-4 and both orthophosphate and orthovanadate is reflected not only in the similar dependence on specific ligands for their enzyme interactions and their apparent competition for the same sites, but also in their common ability to promote ouabain binding. Beryllium also irreversibly inhibits the enzyme, and this inactivation again requires divalent cations, is augmented by K+, but is diminished by Na+ and by ATP. Similarly, prior incubation of the enzyme with vanadate blocks inactivation by beryllium added subsequently. Inactivation by beryllium, however, does not require a halide, and, unlike inactivation by fluoride, increases at basic pHs. These observations suggest that beryllium, as beryllium hydroxide complexes, acts as a phosphate analog, similar to AlF-4 and vanadate.

Reaction sequences for (Na+ + K+)-dependent ATPase hydrolytic activities: new quantitative kinetic models

To delineate better the reaction sequence of the (Na+ + K+)-ATPase and illuminate properties of the active site, kinetic data were fitted to specific quantitative models. For the (Na+ + K+)-ATPase reaction, double-reciprocal plots of velocity against ATP (in the millimolar range), with a series of fixed KCl concentrations, are nearly parallel, in accord with the ping pong kinetics of ATP binding at the low-affinity sites only after Pi release. However, contrary to requirements of usual formulations, Pi is not a competitor toward ATP. A new steady-state kinetic model accommodates these data quantitatively, requiring that under usual assay conditions most of the enzyme activity follows a sequence in which ATP adds after Pi release, but also requiring a minor alternative pathway with ATP adding after K+ binds but before Pi release. The fit to the data also reveals that Pi binds nearly as rapidly to E2 X K X ATP as to E2 X K, whereas ATP binds quite slowly to E2 X P X K: the site resembles a cul-de-sac with distal ATP and proximal Pi sites. For the K+-nitrophenyl phosphatase reaction also catalyzed by this enzyme, the apparent affinities for both substrate and Pi (as inhibitor) decrease with higher KCl concentrations, and both Pi and TNP-ATP appear to be competitive inhibitors toward substrate with 10 mM KCl but noncompetitive inhibitors with 1 mM KCl. These data are accommodated quantitatively by a steady-state model allowing cyclic hydrolytic activity without obligatory release of K+, and with exclusive binding of substrate vs. either Pi or TNP-ATP. The greater sensitivity of the phosphatase reaction to both Pi and arsenate is attributable to the weaker binding by the occluded-K+ enzyme form occurring in the (Na+ + K+)-ATPase reaction sequence. The steady-state models are consistent with cyclical interconversion of high- and low-affinity substrate sites accompanying E1/E2 transitions, with distortion to low-affinity sites altering not only affinity and route of access but also separating the adenine- and phosphate-binding regions, the latter serving in the E2 conformation as the active site for the phosphatase reaction.

Cation sites, spermine, and the reaction sequence of the (Na+ + K+)-dependent ATPase

Spermine, at 0.3 mM, inhibits the K+-nitrophenyl phosphatase activity of a dog kidney (Na+ + K+)-ATPase preparation, increasing the K0.5 for K+, reducing the Km for substrate, and affecting little the inhibition by Na+. These actions can be attributed, in a model of the phosphatase reaction, to parallel decreases in affinity for K+ and Na+ at their cytoplasmically accessible sites. In the (Na+ + K+)-ATPase reaction, spermine increases the K0.5 for Na+ and, to a lesser degree, the K0.5 for K+ as activators. With spermine, the double-reciprocal plots of velocity vs. ATP concentration (in the range 0.3-3 mM), at fixed levels of K+ (from 1 to 10 mM), remain parallel but are rotated clockwise and spread somewhat, reflecting stimulation at low ATP concentrations and inhibition at high ATP but low KCl concentrations. These actions can be attributed, in a steady-state ping-pong model of the ATPase reaction, solely to decreased rates of binding of Na+ and K+ to their sites, with major effects at the cytoplasmically accessible sites for Na+ (acceptance) and K+ (discharge), and with a lesser effect at the extracellularly accessible sites for K+ (acceptance). On these grounds, spermine is a highly specific and potentially valuable reagent for studying the reaction. Furthermore, the model for K+-ATP interactions not only supports a specific reaction sequence (K+ addition, Pi release, ATP addition, K+ release) but also argues against the availability of low-affinity substrate sites except during sharply restricted segments of the reaction sequence, thereby favoring proposals that the low-affinity substrate sites are transformed into high-affinity substrate sites with the E2 to E1 conformational change.

The pharmacokinetics of glibenclamide: a single dose comparison of four preparations in human volunteers

The pharmacokinetic properties of two new HB 420 glibenclamide preparations, Semi-Euglucon N 1.75 mg and Daonil N 1.75 mg, and of two older HB 419 glibenclamide preparations, Semi-Euglucon 2.5 mg and Daonil 2.5 mg, were compared in a randomized cross-over study in eight healthy volunteers. The HB 420 glibenclamide preparations induced peak plasma glibenclamide concentrations up to about 90 ng/ml at 1.3 to 1.4 hours after ingestion. Administration of the HB 419 preparations induced significantly lower peak plasma glibenclamide concentrations at 1.8 to 2.3 hours after ingestion. Glibenclamide was absorbed and eliminated more rapidly after administration of both HB 420 preparations than after administration of the HB 419 preparations. The mean elimination half-life of glibenclamide was 1.3 +/- 0.1 hours in the case of both HB 420 preparations and 2.0 to 2.5 +/- 0.2 hours in the case of HB 419 preparations. Although the HB 420 preparations contained lower doses of glibenclamide than the HB 419 preparations, the AUC values after administration of the former were similar to the AUC value obtained after administration of one of the HB 419 preparations, indicating improved absorption of glibenclamide from the newly developed preparations. However, the other HB 419 preparation was associated with the greatest AUC value of all, suggesting that glibenclamide was absorbed from this preparation almost as completely as from the HB 420 preparations.

Computer prediction of serum theophylline concentrations in ambulatory patients

This study assessed the ability of a computer program Simulated Kinetics (SIMKIN) to predict serum theophylline concentrations in ambulatory patients receiving oral theophylline. Data were collected by retrospective review of prospectively obtained data. A total of only 20 measured serum theophylline concentrations could be included in the study, although records of 195 patients were reviewed. An estimated patient compliance of 90-110% was required and was computed using prescription refill information. Predicted serum theophylline concentrations were generated for each patient by entering into the SIMKIN program the characteristics pertinent to theophylline disposition and the patient's theophylline dosing regimen. Actual and SIMKIN-predicted theophylline concentrations were compared by using simple linear regression and by constructing a 95% confidence interval around the mean prediction error and root mean squared error. The ability of SIMKIN to predict therapeutic category, i.e., subtherapeutic, therapeutic, or toxic, was assessed using Fisher's exact test. SIMKIN predictions of individual theophylline concentration were insufficiently accurate to replace confirmatory followup monitoring of actual levels. However, SIMKIN was able to predict the therapeutic category with 70% accuracy. We conclude that SIMKIN may be useful for categorizing a dose regimen of theophylline as therapeutic, but that it is of little use in predicting individual concentrations in outpatients when literature-averaged pharmacokinetic parameters are the sole criteria for prediction, and compliance cannot be accurately assessed.

Comparison of eight phenytoin dosing methods in institutionalized patients

Until now, no evaluation of phenytoin dosing methods has been undertaken in a large group of patients, to our knowledge. The goal of this study was to determine which of eight different dosing methods most accurately predicts a phenytoin steady-state concentration. Seventy-six patients were chosen, retrospectively, from a state-funded institution for the mentally retarded. Eligibility criteria included two or more different doses of phenytoin and corresponding plasma concentrations. Relative predictive performance was determined by comparing results of simple linear regression. Also, relative bias and precision were determined by comparing mean prediction errors, root mean squared errors, and respective 95% confidence intervals. Of the methods requiring one dose-concentration pair, Rambeck's nomogram was the best predictor of phenytoin concentrations. The methods requiring two known doses and plasma concentrations were more accurate. Their predictive performance was equivalent, although use of the Tozer equation might be preferred for its convenience. None of the methods tested were sufficiently precise to substitute for confirmatory serum phenytoin concentrations.

Pharmacists' views on mandatory patient counseling

A questionnaire was sent to a randomly selected sample of Florida pharmacists to obtain information on the acceptability of mandatory patient counseling. The results of the questionnaire demonstrated that most Florida pharmacists who responded to the survey do not favor a patient counseling regulation. Factors that correlated with a desire for mandatory counseling include: an institutional practice site; assistant director and staff pharmacist position; and a perceived higher income for the patients served by pharmacists. These data indicated that if the mandatory method is selected to stimulate pharmacist-patient interaction, the interrelated issues of reimbursement, facility changes, technician support, patient profiles, continuing education programs, and pharmacists' attitudes toward regulated practice will need to be addressed.

How to establish a pharmacokinetics consulting service for ambulatory patients

Guidelines on establishing a pharmacokinetics consultation service are presented with emphasis on outpatient services. Need for the service must first be demonstrated, using the literature and local data on frequency of serum drug concentration monitoring for particular drugs and patient subgroups. Physician interest in the program must be determined. The pharmacist intervention may be restricted to technical interpretation of serum drug concentration data, or it can include advice based on the patient's disease process, drug effects, and the interaction between the two. In the service described, a patient interview, a chart review, drug analysis, and a written consultation were provided. A flow chart showing movement of the patient through the service was used, and the pharmacist documented the consultation in the patient's medical record, including recommendations for dosage change and follow-up. Cost items to consider in establishing the service include equipment and supplies, space, and personnel. Staff members who are responsible for serum drug analyses must meet state-specific requirements. In estimating revenues, the current number of requests for serum drug concentrations should be doubled and the institution's estimated rate of collection should be used. After the service is established, the cost of a computerized system for pharmacokinetic predictions may be justified by the increased efficiency of such a system.

Accuracy of serum gentamicin concentration predictions generated by a personal-computer software system

Predictions of serum gentamicin concentration and half-life, using a personal-computer software system (SIMKIN [simulated kinetics]), were compared for accuracy as increasing amounts of patient-specific data were supplied to the computer. Data for a two-year period were collected for patients of a hospital's pharmacokinetic consultation service; the study group included adults who had at least one serum concentration for which time of last gentamicin dose was recorded. Input variables were age, weight, height, sex, serum creatinine concentration, concomitant drugs and diseases, gentamicin dosage, time of infusion, dosing interval, number of doses on each regimen, and time and reported value of all serum gentamicin concentrations. Individualized dosing regimens were calculated on the basis of literature estimates, and half-life and serum concentrations were then estimated for these regimens and compared with actual values. One or two measured serum concentrations were then added to the input data. The computer-estimated half-lives (obtained from single-point or two-point analysis in different dosage intervals) were compared with the half-lives determined from actual serum concentration data. Gentamicin serum concentrations were similarly compared. The computer's ability to predict subsequent serum concentrations improved in sequence for literature-averaged prediction and single-point and multipoint analysis. Accuracy of predicting whether peak concentrations were therapeutic or subtherapeutic and whether trough concentrations were toxic also improved as more patient-specific data were input. SIMKIN appropriately evaluated demographic and laboratory data and adequately predicted gentamicin half-lives and serum concentrations.

The oral contraceptive PPI: its effect on patient knowledge, feelings, and behavior

The distribution of the PPI by pharmacists is at best controversial. Although most health professionals agree that the patient has a right to receive information about drugs, they disagree on the best way to provide that information. Since the oral contraceptive PPI has been in routine use for approximately 10 years, a large data base exists that can be used to determine not only patient acceptance of the PPI, but also knowledge, feelings, and behavior secondary to the PPI. In this study, 50 women of childbearing age completed a questionnaire, and it was learned that 84 percent had taken or were currently taking oral contraceptives, and 90 percent of those received a PPI; however, only 61 percent of these women read all of it. The women performed poorly on the knowledge exam (mean +/- SD, 44.5 +/- 21.2, range, 0-83 percent); those who read all of the PPI or who were white had higher scores (p less than 0.02 and p less than 0.001, respectively). Thirty-eight percent of the women thought that the PPI information was inadequate, suggesting that it needs to be rewritten and/or supplemented with information from pharmacists. After reading the PPI, 12 percent contacted their pharmacist for additional information. Pharmacists are in a unique position to provide oral contraceptive information that enables women to make informed judgments regarding benefit:risk ratios on a personal basis.

Effects of pyridoxal phosphate treatment on the (Na + K)-ATPase

Reaction of a dog kidney (Na + K)-ATPase with pyridoxal phosphate, followed by borohydride reduction, reduced the catalytic activity when measured subsequently. The time course of inactivation did not follow a first-order process, and certain characteristics of the residual enzymatic activity were modified. Moreover, various catalytic activities were diminished differently: Na-ATPase activity was largely spared, K-phosphatase activity was diminished only by half that of the (Na + K)-ATPase, whereas (Na + K)-CTPase and Na-CTPase activities were diminished more. ATP, ADP, CTP, nitrophenyl phosphate, and Pi all protected against inactivation. Increasing salt concentrations increased inactivation, but KCl slowed and NaCl hastened inactivation when compared with choline chloride. Occupancy of certain substrate or cation sites seemed more crucial than selection of conformational states. For the residual (Na + K)-ATPase activity the K0.5 for K+ was lower and the K0.5 for Na+ higher, while the sensitivities to ouabain, oligomycin, and dimethylsulfoxide were diminished; for the residual K-phosphatase activity the K0.5 for K+ was unchanged, the sensitivity to ouabain and oligomycin diminished, but the stimulation by dimethylsulfoxide increased. These properties cannot be wholly accommodated by assuming merely shifts toward either of the two major enzyme conformations.

Effects of oligomycin and quercetin on the hydrolytic activities of the (Na+ +K+)-dependent ATPase

Quercetin inhibited a dog kidney (Na+ + K+)-ATPase preparation without affecting Km for ATP or K0.5 for cation activators, attributable to the slowly-reversible nature of its inhibition. Dimethyl sulfoxide, a selector of E2 enzyme conformations, blocked this inhibition, while the K+-phosphatase activity was at least as sensitive to quercetin as the (Na+ + K+)-ATPase activity, all consistent with quercetin favoring E1 conformations of the enzyme. Oligomycin, a rapidly-reversible inhibitor, decreased the Km for ATP and the K0.5 for cation activators, and its inhibition was also diminished by dimethyl sulfoxide. Although oligomycin did not inhibit the K+-phosphatase activity under standard assay conditions, a reaction presumably catalyzed by E2 conformations, its effects are nevertheless accommodated by a quantitative model for that reaction depicting oligomycin as favoring E1 conformations. The model also accounts quantitatively for effects of both dimethyl sulfoxide and oligomycin on Vmax, Km for substrate, and K0.5 for K+, as well as for stimulation of phosphatase activity by both these reagents at low K+ but high Na+ concentrations.

Comparison of standard and modified enzyme immunoassay of phenytoin

A modified method for the enzyme immunoassay (EMIT, Syva Company) of phenytoin is presented and compared with the standard method. Serum samples from 14 patients were analyzed for phenytoin content using both methods. All assays were performed by the same individual. Within-day and between-day variations of the modified method were determined. A carry-over study was done to determine if a sample with a high phenytoin concentration might contaminate subsequent samples with lower concentrations or whether samples with low concentrations could dilute subsequent samples with higher concentrations. Within-day and between-day variations of the modified method were 7.5% and 9.9%, respectively. These values are less than the 10% coefficient of variation limit claimed by the manufacturer of the standard method. The carry-over study revealed no significant carry-over with the modified method. An excellent correlation was observed between the values obtained from the two methods. The modified method can reduce assay costs by up to 40%. The modified method was found to provide accuracy and precision equivalent to the standard EMIT method at a substantial cost savings.

The absorption of intramuscular chlordiazepoxide (Librium) in patients with severe alcoholic liver disease

Intramuscular chlordiazepoxide (CDX) is commonly administered to alcoholic liver disease (ALD) patients requiring prompt management of alcohol agitation, anxiety, and delirium tremors. Sedative action is associated with plasma levels of approximately 2.0 mcg/ml, however, intramuscular CDX has been shown to produce peak concentrations consistently below 2.0 mcg/ml in normal subjects. The present study was designed to define the absorption characteristics of intramuscular 25 mg CDX in males with ALD. Five normal males had mean CDX absorption half-lives of 3.0 h and peaked at 0.8 mcg/ml in 7.2 h, while 11 males with ALD had mean absorption half-lives of 9.0 h, and peaked at 0.7 mcg/ml in 19.1 h when they received the drug dissolved in normal saline. Four other males with ALD who received CDX dissolved in the manufacturer's diluent had significantly slower mean absorption half-lives of 16.1 h which peaked at 0.3 mcg/ml in 35.2 h. Significant linear correlations were found with age (r = 0.60, p less than 0.01), body weight (r = 0.55, p less than 0.01), and serum albumin (r = 0.60, p less than 0.01). Because of the extremely slow intramuscular absorption of CDX dissolved in normal saline or the manufacturer's diluent in males with ALD, we do not recommend this route of administration in this population.