Effect of serum separator blood collection tubes on drug concentrations

Using the EMIT assay, we tested clinical samples from patients receiving 12 commonly monitored drugs to evaluate the effect of serum separator gel contained in serum separator blood collection tubes (SST) (Becton-Dickinson). There were significant concentration decreases for lidocaine, pentobarbital, and phenytoin. In vitro experiments demonstrated that this effect on phenytoin was dependent on time of exposure to the gel and volume of whole blood, but was not dependent on the presence of red blood cells or initial concentration. Bias attributed to the use of SST could interfere with the usefulness of clinical results at the upper and lower limits of the therapeutic range. This problem can be minimized by processing samples of at least 2 ml within 1 h.

Metabolism of loprazolam in rat, dog and man in vivo

The metabolism of 14C-loprazolam has been studied in rat, dog and man in vivo. In rat, the major metabolic pathways were hydroxylation on the benzodiazepine ring, and reduction and acetylation of the nitro group. Both metabolites were identified by co-chromatography with standards, and were present in urine and bile conjugated with glucuronic acid. In both dog and human urine and bile significant amounts of the piperazine-N-oxide were found. This N-oxide was identified by co-chromatography with authentic compound and by mass spectroscopy. Both loprazolam and the dog biliary metabolites were hydrolysed spontaneously to polar material. Neither treatment with beta-glucuronidase nor incubation with gut microflora had any further effect. Only polar metabolites were found in dog and human faeces. The principal non-polar material found in rat plasma was the diazepine-hydroxy compound, and little loprazolam was present. Significant levels of loprazolam and lower levels of an unidentified metabolite were found in ether extracts of dog and human plasma. Both the piperazine-N-oxide and loprazolam were found in similar quantities in chloroform extracts of human plasma, and at two hours after dosage, the N-oxide and loprazolam accounted for greater than 90% of the radioactivity present in the plasma.

Conversion from intravenous aminophylline to sustained-release theophylline: computer simulation versus in vivo results

The accuracy of computer-predicted theophylline serum concentrations compared with actual serum concentrations in patients whose drug therapy was being converted from aminophylline infusions to an oral sustained-release theophylline product (Theo-Dur) was measured. The SIMKIN computer program was used to simulate theophylline serum-concentration curves in nine patients receiving an initial dose of sustained-release theophylline at the time their maintenance aminophylline infusions were discontinued. The sustained-release theophylline doses were calculated using individual patient theophylline clearance values to produce mean theophylline serum concentrations in the normal therapeutic range. Pharmacokinetic variables used in the SIMKIN program were derived from individual patients' serum concentrations and average literature values. Theophylline serum concentrations were measured before the initial dose of the sustained-release product and periodically for 12 hours. Mean SIMKIN-predicted serum theophylline concentrations were within 10% of actual measurements 39% of the time, but data from individual patients varied considerably. Two patients had prolonged absorption lag times that could not be explained. Computer-simulation programs using population-based pharmacokinetic variables to predict theophylline serum concentrations must be tested against in vivo measurements to verify their accuracy.

A model for the reaction pathways of the K+-dependent phosphatase activity of the (Na+ + K+)-dependent ATPase

(Na+ + K+)-dependent ATPase preparations from rat brain, dog kidney, and human red blood cells also catalyze a K+ -dependent phosphatase reaction. K+ activation and Na+ inhibition of this reaction are described quantitatively by a model featuring isomerization between E1 and E2 enzyme conformations with activity proportional to E2K concentration: (formula; see text) Differences between the three preparations in K0.5 for K+ activation can then be accounted for by differences in equilibria between E1K and E2K with dissociation constants identical. Similarly, reductions in K0.5 produced by dimethyl sulfoxide are attributable to shifts in equilibria toward E2 conformations. Na+ stimulation of K+ -dependent phosphatase activity of brain and red blood cell preparations, demonstrable with KCl under 1 mM, can be accounted for by including a supplementary pathway proportional to E1Na but dependent also on K+ activation through high-affinity sites. With inside-out red blood cell vesicles, K+ activation in the absence of Na+ is mediated through sites oriented toward the cytoplasm, while in the presence of Na+ high-affinity K+ -sites are oriented extracellularly, as are those of the (Na+ + K+)-dependent ATPase reaction. Dimethyl sulfoxide accentuated Na+ -stimulated K+ -dependent phosphatase activity in all three preparations, attributable to shifts from the E1P to E2P conformation, with the latter bearing the high-affinity, extracellularly oriented K+ -sites of the Na+ -stimulated pathway.

Determination of ideal body weight for drug dosage calculations

Formulas for ideal body weight (IBW) in men and women were derived from the Metropolitan Life Insurance Company height and weight tables. Regression determinations of median weight versus height were performed for men and women. A program for a minicomputer was developed to generate plots for small, medium, and large frame sizes and for subjects of all frame sizes. Equations for ideal body weight were derived from the resulting data. For men of all frame sizes, IBW = 51.65 kg + 1.85 kg/inch of height greater than 5 feet. For women of all frame sizes, IBW = 48.67 kg + 1.65 kg/inch of height greater than 5 feet. More accurate estimates of IBW by frame size can be obtained using equations derived from the plots for men and women of each frame size. Estimates of IBW obtained by the widely used empirical method probably contain only minor errors. However, formulas derived from actual height and weight data should be used in pharmacokinetic determination of dosage regimens for some drugs.

The effect of ibuprofen on serum digoxin concentrations

This study was undertaken to determine the effects of ibuprofen (Motrin), in daily doses of at least 1600 mg, on steady-state digoxin concentrations. A total of 12 ambulatory patients (10, female; 2, male), with a mean age of 66 years (38-81 yr), completed the study. An initial baseline serum digoxin level was obtained, with follow-up levels at 7 days and, whenever possible, 28 days after ibuprofen initiation. Serum creatinine concentrations were not significantly different from baseline to 7 or 28 days of ibuprofen therapy. Results show a statistically significant (p less than 0.05) increase in digoxin levels after seven days of ibuprofen. The mean increase was 59 percent (range, 10.7-325.4 percent), with 10 of the 12 patients displaying increased seven-day levels. Digoxin levels drawn 28 days after ibuprofen initiation were not statistically different from baseline or seven-day digoxin levels.

Pharmaceutical services in family practice medical residency training programs

The extent and nature of pharmacists' involvement in family practice medical residency training programs was assessed using a national survey. Department chairmen of all 386 approved family practice residency training programs in the United States were contacted and asked to provide the names and addresses of pharmacists in charge of pharmaceutical services in the centers. A 46-item, six-page questionnaire was mailed to each pharmacist with a follow-up mailing, then a telephone call, to nonresponders. Department chairmen of 68 (18%) of the programs reported having at least one pharmacist in the center. Responses to the questionnaire were obtained from 53 (78%) of the pharmacists, four of whom were no longer involved with family practice centers. Most of the remaining 49 pharmacists were men (76%) between 30 and 40 years old (59%) with an academic appointment (67%) and a doctor of pharmacy degree or some type of postgraduate training. Drug-distribution services were provided in 37% of the centers. All pharmacies offered clinical services. Almost all pharmacies (92%) offered educational services to both medical and nursing staffs, and pharmacists in 74% of the centers were involved in research. Few family practice medical residency training centers have pharmaceutical services conducted by a pharmacist; centers with pharmacists have a wide variety of distributive and clinical services.

Kinetic studies on the (Na+ + K+)-dependent ATPase evidence for coexisting sites for Na+, K+ and Mg2+

Na+-ATPase activity of a dog kidney (Na+ + K+)-ATPase enzyme preparation was inhibited by a high concentration of NaCl (100 mM) in the presence of 30 microM ATP and 50 microM MgCl2, but stimulated by 100 mM NaCl in the presence of 30 microM ATP and 3 mM MgCl2. The K0.5 for the effect of MgCl2 was near 0.5 mM. Treatment of the enzyme with the organic mercurial thimerosal had little effect on Na+ -ATPase activity with 10 mM NaCl but lessened inhibition by 100 mM NaCl in the presence of 50 microM MgCl2. Similar thimerosal treatment reduced (Na+ + K+)-ATPase activity by half but did not appreciably affect the K0.5 for activation by either Na+ or K+, although it reduced inhibition by high Na+ concentrations. These data are interpreted in terms of two classes of extracellularly-available low-affinity sites for Na+: Na+-discharge sites at which Na+-binding can drive E2-P back to E1-P, thereby inhibiting Na+-ATPase activity, and sites activating E2-P hydrolysis and thereby stimulating Na+-ATPase activity, corresponding to the K+-acceptance sites. Since these two classes of sites cannot be identical, the data favor co-existing Na+-discharge and K+-acceptance sites. Mg2+ may stimulate Na+-ATPase activity by favoring E2-P over E1-P, through occupying intracellular sites distinct from the phosphorylation site or Na+-acceptance sites, perhaps at a coexisting low-affinity substrate site. Among other effects, thimerosal treatment appears to stimulate the Na+-ATPase reaction and lessen Na+-inhibition of the (Na+ + K+)-ATPase reaction by increasing the efficacy of Na+ in activating E2-P hydrolysis.

EMIT theophylline assay at reduced cost

An experiment was designed to determine if a new EMIT theophylline method that reduces reagent costs can maintain the standard EMIT method's high degree of accuracy and precision. Eight known theophylline concentrations ranging from 1.5 to 75 micrograms/ml were analyzed by both methods. Two hundred five assays were performed on study patients using the new method. During 4 months of clinical service, 51 assays, ranging from 0 to 51 micrograms/ml, were performed by the standard method, and during the following 12 months 213 clinical service assays, ranging from 0 to 35.6 micrograms/ml, were performed by the new method. A strong correlation (r = 0.997) was demonstrated between the new and standard EMIT methods. Both methods had similar variance and curve stability. A 56% reduction in reagent expenses was realized with the new method over a 12-month period.

Prediction of serum concentrations of digoxin in a family practice center

Physicians and clinical pharmacists were compared in their ability to predict serum digoxin concentrations and to discriminate among patients who were subtherapeutic, therapeutic or toxic. Physicians correctly predicted patients having therapeutic serum digoxin concentrations 77 percent of the time, but they were unable to reliably identify subtherapeutic and toxic patients. By incorporating more compliance and pharmacokinetic data into their assessment, pharmacists proved to be more accurate than physicians both in the prediction of serum digoxin concentrations (P less than .01) and in therapeutic classifications (P less than .001). The clinical pharmacist can be a valuable aid to the physician in the prediction and interpretation of serum digoxin concentrations.

Tryptic digestion of the (Na + K)-ATPase is both sensitive to and modifies K+ interactions with the enzyme

Tryptic digestion of the (Na + K)-ATPase in the presence of choline chloride or NaCl ("Na-type") and in the presence of KCl ("K-type") produced distinct patterns of peptide fragments and losses of catalytic activity. The K0.5 for K+ to shift digestion from the Na-type, and its sensitivity to dimethyl sulfoxide and Triton X-100, were consistent with K+ acting at sites on the cytoplasmic face of the enzyme through which the K-phosphatase reaction also is activated. Reagents favoring the E1 conformational states, oligomycin, Triton, and ATP, shifted the pattern toward the Na-type, whereas those favoring E2 states, dimethyl sulfoxide, MgCl2, and MnCl2, shifted the pattern toward the K-type. Na-type digestion caused a greater loss of K-phosphatase than (Na + K)-ATPase activity, and the residual K-phosphatase activity was more sensitive to inhibition by Triton and ATP but stimulated more by dimethyl sulfoxide and inhibited less by Pi and MnCl2; all these effects are consistent with such digestion shifting equilibria toward E1 enzyme states. Accordingly, the K0.5 for K+ to activate the (Na + K)-ATPase was increased. However, the K0.5 for the K-phosphatase was unchanged; this observation requires revision of previous formulations, and bears on additional aspects of enzyme activity as well.

Substrate interactions with brain (Ca + Mg)-ATPase

ATP hydrolysis by a partially purified (Ca + Mg)-ATPase preparation from rat brain increased with substrate concentration in a biphasic fashion, with apparent Km values of 3 microM and 0.1 mM. Ca-dependent phosphorylation, however, had only a single Km value, 3 microM. KCl increased ATPase activity in both concentration ranges, but the K0.5 for KCl decreased from 7 mM to 0.3 mM as the ATP concentration was reduced from 1 mM to 10 microM. The K0.5 for MgCl2 decreased somewhat less, from 3 mM to 0.6 mM with ATP concentrations from 1 mM to 1 microM, but was far lower for steady-state phosphorylation, 0.03 mM. (Ca + Mg)-dependent hydrolysis was not demonstrable with other nucleotide triphosphates or p-nitrophenyl phosphate, and these substances, as well as a reaction product, Pi, were also inhibitors. On the other hand, ADP inhibited at both ATP concentration ranges, and also stimulated dephosphorylation. This pattern of responses to substrate and cations is reminiscent of that of well-characterized transport ATPases, suggesting similar roles and mechanisms.

Influence of cimetidine on oral diazepam elimination with measurement of subsequent cognitive change

In a double-blind crossover design, the effect of cimetidine on oral diazepam pharmacokinetics and an evaluation of cognitive function change was studied in seven healthy volunteers. Subjects randomly received placebo or cimetidine 300 mg orally every 6 h for a total of five doses prior to diazepam 10 mg. A significant increase in diazepam elimination half-life from (mean +/- s.e. mean) 66.9 +/- 21.4 to 89.6 +/- 22.5 h (P = 0.006) and area under the plasma concentration-time curve from 5.06 +/- 1.47 to 8.93 +/- 1.88 micrograms ml-1 h (P = 0.028) was observed indicating a probable cimetidine induced inhibition of diazepam hepatic metabolism. Digit symbol substitution and visual analogue scales were used to measure the effect of an alteration of diazepam kinetics on cognitive function. An enhancement of pharmacological effect as reflected in digit symbol substitution scores and visual analogue scale measurements was not observed.

Prediction of theophylline dosage regimens from limited serum sampling

Intravenous aminophylline was administered to 13 subjects (6 normal, 7 with chronic obstructive pulmonary disease), and multiple blood specimens were drawn over an 8-hour period for theophylline analysis. Half of the samples were obtained during the distribution phase of the drug and the remainder during the elimination phase. These data were entered into a computer program that both calculates and graphically displays individual two-compartment pharmacokinetic data, and recommends a dosing regimen. Analysis of these data demonstrates wide variability in the theophylline volume of distribution, half-life, and predicted dosage regimen. Dosage regimens can be individualized by obtaining two specimens for theophylline analysis during the elimination phase after intravenous administration of the drug; these regimens correlate extremely well (r2 = 0.95) with those designed using all the data points.

Optimal lidocaine dosing in patients with myocardial infarction

A decrease in hepatic clearance and volume of distribution in patients with congestive heart failure frequently leads to toxicity when drugs such as lidocaine are administered. To determine the effect of adjusted dosing of lidocaine in patients with myocardial infarction, we studied 32 patients receiving lidocaine either by a conventional method (control group: 1-2 mg/kg bolus, then 1 to 4 mg/min) or by an adjusted regimen based on the presence or absence of heart failure [experimental group: 1-2 mg/kg bolus; then, class I (no heart failure), 35 to 88 micrograms/kg/min; class II (heart failure), 12 to 35 micrograms/kg/min]. Plasma lidocaine levels were determined at 2 and 5 h of the infusion by enzyme multiplied immunoassay technique (EMIT) and gas liquid chromatography (GLC). Ten of 33 determinations in the control group were in the toxic range, i.e., greater than 6 micrograms/ml, and four others were subtherapeutic, i.e., less than 2 micrograms/ml. In contrast, 13 of 16 determinations in the experimental group were in the therapeutic range, and none were in the toxic range. These data show that administration of lidocaine by a conventional method may produce diverse plasma levels that may occasionally be in the toxic range. Modified dosing based on cardiac status may result in optimal levels in most patients.

Antibiotic prescribing in a family medicine residency program

A total of 227 ambulatory patients who received prescriptions for antibiotics in a family practice residency program was studied. The common infections treated were urinary tract infections, upper respiratory tract infections, impetigo, nonspecific vaginitis, and bronchitis. Cultures obtained in 21.1 percent of the patients were usually considered to be appropriate. Urinary tract infections were usually treated with co-trimoxazole or other drugs containing sulfonamides; upper respiratory tract infections with amoxicillin, ampicillin, or penicillin; impetigo with penicillin; nonspecific vaginitis with vaginal creams; and bronchitis with ampicillin or erythromycin. Most prescriptions (86 percent) were written generically at an approximate savings of $2 per prescription. A review panel audited the prescribing practices and often (32.2 percent) disagreed among themselves, yet they did determine 65.4 percent of the prescriptions to be appropriate. The rate of appropriate antibiotic prescribing practices among the residents was found to decrease as the level of supervision decreased (P less than 0.01).

Investigation of a dosage regimen for intravenous theophylline

A study was designed to evaluate the validity of the dosage guidelines for theophylline recommended by Hendeles and Weinberger. A total of seven asthmatic smokers and non-smokers were entered and studied. Theophylline serum concentrations were determined prior to the start of therapy and at intervals following initiation of an infusion. The mean theophylline concentration attained for all subjects was 10 micrograms/ml, however, five of the six patients completing the study did not achieve the predicted serum theophylline concentration. Further study of higher dosage designed to achieve a concentration of 12 micrograms/ml is suggested.

A comparison of various types of patient instruction in the proper administration of metered inhalers

The administration technique employed by 42 inpatients using metered inhalers were observed. Proper performance of the six steps recommended by the manufacturer provided the guidelines for correct administration. The degree of compliance with proper technique was defined as the number of steps correctly executed by the patient. The mean number of steps correctly performed was 2.9 out of the possible six (48.3 percent). Twenty-four patients were then randomized into one of three groups. Group I received the manufacturer's instruction sheet, Group 2 received counseling from a pharmacist, and Group 3 received both the manufacturer's instruction sheet and counseling from a pharmacist. There was a significant improvement in the postinstruction technique in Groups 2 and 3, while Groups 1 failed to demonstrate any significant improvement. Comparisons were then made among the three groups. No significant difference was found between Group 2 and Group 3. However, both Groups 2 and 3 were found to be significantly different (p less than 0.05) from Group 1. This study shows that pharmacist counseling can significantly improve the degree of patient compliance in the administration of metered inhalers.

A pharmacy student searches for psychological predictors of patient compliance

Pharmacists are becoming more involved in patient counseling and dosage regimen design in an attempt to improve patient compliance. A study was designed and implemented by an undergraduate pharmacy student in an attempt to gain experience in research methodology and to enhance individual clinical involvement. Forty patients, randomly selected at a community pharmacy and a family practice clinic, were administered a Myers-Briggs Type Indicator exam to assess the patient's degree of systematic preference. Refill dates for each patient's hypertensive medications were examined for six months in order to infer compliance. Results of the psychological exam did not accurately predict patient compliance or noncompliance. The student working with only minimal faculty guidance was able to design, implement, analyze, and describe the study. Colleges of pharmacy are encouraged to implement similar clinical research training projects for undergraduate students.