The effect of humidity on samples of microcrystalline cellulose taken from the extrusion/marumerization process

The purpose of this work was to examine the sorption and desorption of water by various samples of microcrystalline cellulose, MCC (Avicel PH-101), taken from the extrusion/marumerization process, and to provide data that may explain how water affects the MCC polymer matrix during the formation of beads. Two isopiestic (humidity) studies were conducted: the first used samples exposed directly to controlled humidity conditions, whereas the second used samples that were freeze-dried before being exposed to controlled humidity conditions. Water sorption and desorption were determined gravimetrically. When both sets of samples were initially exposed to low-humidity conditions, they reached equilibrium by desorbing water. When these samples were initially exposed to high-humidity conditions, the high moisture content samples desorbed water, whereas the low moisture content and the freeze-dried samples sorbed water to reach equilibrium. When the first set of samples was initially exposed to high- and then to low-humidity conditions, they reached the same water content achieved by being equilibrated directly at the low-humidity condition. However, samples that were initially exposed to low- and then to high-humidity conditions had equilibrium water contents that were lower than those achieved by being equilibrated directly at the high-humidity condition. The original MCC systems exhibit a hysteretic effect above 85%, whereas the freeze-dried systems have a broader range hysteretic effect starting at 20% relative humidity. The results suggest that the internal structure of the MCC polymer fibers must change with the sorption and desorption of water, supporting the autohesion theory.

Drug release from film-coated chlorpheniramine maleate nonpareil beads: water influx and development of a new drug release model

The purpose of this work was to investigate drug release from film-coated chlorpheniramine maleate (CPM) nonpareils (sugar spheres) and the effect of water influx on the drug release mechanism. The methods used in the study involved the layering of CPM onto nonpareil cores using a fluid-bed apparatus. These CPM cores were then coated with an aqueous ethylcellulose dispersion, which was blended with a solution of hydroxylpropylmethylcellulose (HPMC) at different concentrations. The net water influx was determined by measuring water uptake during dissolution. The film surface area was calculated from bead diameters measured with an optical microscope. Drug release profiles were measured using USP dissolution method I (basket). The results showed that significant water influx occurred, which produced an internal liquid phase ranging from 0 to 1.8 x 10(3) mm3/g of sample. As a result of the water uptake, an increase in bead size was observed. The bead surface area varied over the range of 40-80 x 10(3) mm2/g sample because of a combined effect of the water uptake and the release of the bead contents. A bead geometry parameter was proposed as the ratio of the bead surface area to the volume of the internal liquid phase. This bead geometry parameter was measured as a function of time and fit to an equation using a computer curve-fitting technique. This equation was substituted into an existing drug release model to give a more appropriate mathematical model describing drug release from this system. The conclusion drawn from these results is that the influx of water during drug dissolution creates a progressive increase in the liquid phase within the nonpareil bead; this causes a corresponding increase in the bead surface area which influences the drug release rate.

Oral contraceptive therapy in women: drug interactions and unwanted outcomes

Oral contraceptives are highly effective contraceptive agents used worldwide that have a relatively low incidence of adverse side effects. Drug interactions that decrease the efficacy of contraception or that limit the efficacy of concomitant medications can occur. The most frequent clinically encountered interactions involve antibiotics or anticonvulsants. The incidence of adverse thrombotic events is low and can be further minimized by the use of low estrogen doses; avoidance of smoking or not prescribing oral contraceptives in smokers; and avoidance of exposure in genotypes at high risk for thrombosis (Leiden Factor V mutation).

Gender differences in response to drugs: pain medications

Differences exist between men and women in both perception of and response to pain. Whereas gender-related differences in pharmacokinetics may have confounded earlier studies of pain responses, emerging scientific evidence suggests gender-related pharmacologic differences in central nervous system opioid mu-receptor binding and in responses to kappa-opioid pain medications. These differences suggest the importance of developing gender-specific strategies for pain relief and highlight the need for further investigation of gender-related pain treatment strategies.

In vivo comparison of putative probes of CYP3A4/5 activity: erythromycin, dextromethorphan, and verapamil

OBJECTIVES

Multiple in vivo CYP3A4/5 probes have been proposed. We compared verapamil clearance measures (CYP3A4/5 substrate) to the erythromycin breath test (ERBT) and the cumulative urinary dextromethorphan/3-methoxymorphinan test.

METHODS

Clearance of intravenous and oral racemic verapamil and the area under the plasma concentration versus time curve (AUC) ratio of norverapamil (N-demethylated metabolite) to verapamil after oral verapamil dosing, the ERBT, and the dextromethorphan urinary metabolite ratios were measured in 84 healthy nonsmoking subjects (42 men and 42 women; age, 47 +/- 23 (mean +/- SD) years; weight, 69 +/- 11 kg). Relationships between putative CYP3A4/5 probes were assessed by linear regression.

RESULTS

The strongest correlation was between intravenous and oral verapamil clearance (r2 = 0.26; P = .0001). Relationships between cumulative urinary dextromethorphan/3-methoxymorphinan and (1) intravenous verapamil clearance (r2 = 0.073; P = .024), (2) oral verapamil clearance (r2 = 0.144; P = .001), and (3) plasma AUC(norverapamil)/AUC(verapamil) after oral verapamil (r2 = 0.10; P = .01) were also detected. The ERBT and intravenous verapamil clearance were weakly related (r2 = 0.04; P = .067). No relationship was detected between ERBT and dextromethorphan/3-methoxymorphinan ratios (r2 = 0.00006; P = .945), oral verapamil clearance (r2 = 0.00006; P = .94), or plasma AUC(norverapamil)/AUC(verapamil) after oral verapamil (r2 = 0.0002; P = .9).

CONCLUSIONS

Intravenous and oral verapamil clearance values were significantly correlated, and cumulative dextromethorphan/3-methoxymorphinan urinary ratios correlated with both plasma AUC(norverapamil)/AUC(verapamil) after oral verapamil dosing and with oral and intravenous verapamil clearance. The ERBT correlated only weakly with intravenous verapamil clearance. Results with verapamil are comparable to results with other intravenous and oral CYP3A4/5 probes. Lack of correlation between putative CYP3A4/5 probe results may be attributable to the route of administration; probe characteristics; and intersubject, intrasubject, between-day, and testing measurement variability.

Cardiovascular pharmacology of aging

Despite the relative paucity of drug trials in the old and especially the very old (> 85 years), some general principles of pharmacology in the aging patient can be taken from available data and clinical experience. The pharmacokinetic changes most consistently seen with aging occur in the volume of distribution, clearance, and half-life of a drug. Renal drug clearance is consistently diminished with aging. Hepatic metabolism is more variably affected, and in contrast to renal clearance, no reliable formula exists to estimate hepatic drug clearance. Pharmacodynamic changes, although present, are less well studied or described in the elderly. Drug interactions and adverse drug reactions increase with increasing numbers of medications prescribed and represent a complex interplay of age, underlying disease, and number and types of medications. The clinical caveats that apply to drug prescription in the very old include reduced starting doses with slow incremental increases; elimination of unnecessary medications; and anticipating and monitoring for drug interactions and ADRs, especially when prescribing warfarin, digoxin, and amiodarone. Future studies that look at the aging patient in the presence of effects of age, physiology, gender, comorbid illness, and multiple drug therapies may help evolve a new set of paradigms for geriatric drug prescribing.

Microencapsulation of chlorpheniramine maleate-resin particles with crosslinked chitosan for sustained release

Formulation and preparation parameters of drug/ion-exchange particles microencapsulated in cross-linked chitosan were evaluated for controlled release of the water-soluble drug chlorpheniramine maleate (CPM) in a suspension. An emulsion solvent evaporation method was used to produce CPM-resinates embedded in glutaraldehyde (GTA) crosslinked chitosan microspheres (MCSs). Crosslinking extent in the chitosan was monitored by swelling measurements. Controlled release was evaluated by dissolution tests in simulated gastric fluid without enzyme (SGF) and in simulated intestinal fluid without enzyme (SIF). CPM-resinates contained 62% (w/w) of drug. MCSs were spherical, ranging from 82 to 420 microns in diameter, and contained multiple resinates. The sizes of MCSs prepared with safflower oil and Span 80 were controlled by surfactant concentration, stirring speed, and duration of stirring. Maximum crosslinking was produced with 240 mg GTA per 250 mg of chitosan. Maximum drug release from free CPM-resinates was about 60% by 1 hr in SGF, and was about 100% by 3 hr in SIF. CPM release was slower from MCSs crosslinked with 120 mg of GTA compared to 5 mg GTA in both media. By 8.3 hr, the more crosslinked MCSs released about 30% CPM in SGF, and about 60% in SIF. Because of the apparent ceiling on release in SGF, the final experiments were conducted in SIF. Increasing the weight ratio of the chitosan coating to CPM-resinate ratio from 1:1 to 4:1 moderately decreased release profiles carried out to 33 hr. Increasing MCS diameters from 82 to 163 microns moderately decreased release profiles. Microencapsulation of CPM-resinates with crosslinked chitosan demonstrated controlled release of CPM in SGF and SIF without enzymes. The retardation effect increased when the crosslinking extent and chitosan to resin ratio increased.

The ACC professional life survey: career decisions of women and men in cardiology. A report of the Committee on Women in Cardiology. American College of Cardiology

OBJECTIVES

This survey was conducted to learn how the career decisions of women and men in cardiology influenced their professional and personal lives.

BACKGROUND

Women represent only 5% of practicing adult cardiologists and 10% of trainees. Yet, women and men now enter medical school at nearly equal numbers. The factors that contribute to career satisfaction in cardiology should be identified to permit the development of future strategies to ensure that the best possible candidates are attracted to the profession.

METHODS

A questionnaire developed by the Ad Hoc Committee on Women in Cardiology of the American College of Cardiology (ACC) was mailed in March 1996 to all 964 female ACC members and an age-matched sample of 1,199 male members who had completed cardiovascular training.

RESULTS

Women were more likely to describe their primary or secondary role as a clinical/noninvasive than invasive cardiologist (p < 0.0001 women vs. men). Men and women both reported a high level of satisfaction with family life, but women were less satisfied with their work as cardiologists (88% vs. 92%, p < 0.01) and with their level of financial compensation. Compared with men, women expressed less overall satisfaction (69% vs. 84%) and more dissatisfaction with their ability to achieve professional goals (21% vs. 9%). These differences were most pronounced for women in academic practice. Women reported greater family responsibilities, which may limit their opportunities for career advancement. Women were more likely to alter training or practice focus to avoid radiation. A majority of women (71%) reported gender discrimination, whereas only 21% of men reported any discrimination, largely due to race, religion or foreign origin.

CONCLUSIONS

Women cardiologists report overall lower satisfaction with work and advancement, particularly within academic practice. They report more discrimination, more concerns about radiation and more limitations due to family responsibilities, which may ultimately explain the low percentage of women in cardiology. Attention to these issues may result in programs to improve professional satisfaction and attract the best candidates into cardiology in the future.

Introduction of dissolution error as a result of different openings in vessel covers

Vessel covers are required in dissolution studies to retard solvent evaporation. Sufficient openings on the cover are required by the current United States Pharmacopeia (USP) "to allow ready insertion of a thermometer and for withdrawal of specimens/samples." However, the area of the opening has not been regulated by the USP. The purpose of this work was to measure the loss of the dissolution solvent as a result of openings in vessel covers and to investigate errors caused by the solvent loss. The method used in the study involved measurements of the opening areas in three commercial vessel covers and determinations of solvent loss under a typical dissolution condition. The results showed that the openings in the three covers varied from 75 mm2 to 2285 mm2; this was 1-30% of the total vessel open area for a USP standard vessel. The volume of the dissolution solvent was reduced by 0.6-3.4% for an 8-hr dissolution study, and 1.7-9.7% for a 24-hr study when the three different vessel covers were used. The rate of solvent loss exhibited a linear relationship with the area of the opening in the covers. A slower rate of reduction was found for a smaller initial volume of the solvent. The conclusion was that higher dissolution results were produced if the solvent loss was not considered.

Age effects on interrelationships between lung volume and heart rate during standing

To determine the effects of aging and posture on the relationship between respiration and heart rate (HR), we collected 5 min of lung volume and R-R interval data from 7 young (27 +/- 3 yr, mean +/- SD) and 10 old (69 +/- 6 yr) healthy humans during spontaneous breathing while they were supine (SU) and standing (ST). Lung volume and HR power spectra and transfer functions between lung volume and HR were estimated. Age and position effects and age-position interactions were determined by analysis of variance for repeated measures. Older subjects had a lower and more variable respiration rate (P < 0.03, P < 0.04), but both age groups exhibited decreased rate of respiration and increased tidal volume with ST (P < 0.05, P < 0.005). ST decreased lung volume-to-HR transfer function magnitude in both groups (P < 0.07). The more marked age-related differences were in phase angle. Both SU and ST phase angles were greater in older subjects (P < 0.003). ST decreased phase angle in young but increased phase angle in older subjects (P < 0.001). In conclusion, respiration, and respiration-HR interrelationships are altered by aging, with increased time delays between lung volume and HR and altered relationships with ST.

Dopaminergic responses in the Fischer 344 rat heart: preserved chronotropic and dromotropic responses with aging

BACKGROUND

Marked decreases in cardiac responses to beta-adrenergic stimuli have been found in cellular, animal, and human models of physiologic aging. As another probe of receptor-regulated cardiovascular changes with aging, responses to dopamine were studied. Responses were studied with and without depletion of myocardial catecholamines to eliminate effects secondary to myocardial catecholamine release.

METHODS

Responses of heart rate (A-A intervals), atrioventricular conduction (AV intervals and AV Wenckebach block cycle length) to 0-50 microM dopamine were studied in Langendorff perfused hearts from 10 mature (6.2 +/- 0.8 mo, mean +/- SD) and 9 senescent (23.6 +/- 0.7 mo) Fischer 344 rats and in hearts from 10 mature (5.3 +/- 0.4 mo) and 8 senescent (23.9 +/- 0.8) Fischer 344 rats after myocardial catecholamine depletion by reserpine (0.25 mg/kg i.p. x 5 days).

RESULTS

Dopamine decreased A-A (p < .0001) and AV conduction intervals (p < .0001) and increased peak developed pressure (p < .0001) and dP/dt (p < .001) in hearts from nonreserpine treated mature and senescent rats. Greater decreases in A-A intervals and AV conduction were seen in senescent compared to mature hearts (p < .0001). Contractile responses were greater in mature hearts (p < .001). After reserpine, A-A interval and paced AV conduction dose vs response relationships shifted rightward (p < .0001), but peak responses and age-related differences in responses were not significantly affected. In contrast, increases in peak developed pressure were greatly reduced in mature hearts (p < .0001) and age-related differences in contractile responses to dopamine were eliminated in hearts from reserpine-treated rats.

CONCLUSIONS

(a) A-A interval and AV conduction responses to dopamine were greater in senescent hearts even after catecholamine depletion, suggesting age-related differences in sinus and AV nodal responses to direct dopaminergic stimuli exist. (b) Age-related differences in contractile responses to dopamine were eliminated by reserpine suggesting basal age-related differences in response were secondary to age-related differences in responses to myocardial catecholamine release.

Differences in the mechanical strength of dried microcrystalline cellulose pellets are not due to significant changes in the degree of hydrogen bonding

The mechanical strengths of oven-dried pellets of microcrystalline cellulose, MCC, prepared by extruder/marumerizer technology are weaker when ethanol/water mixtures are used as granulating solutions than when granulated with water. Previously, the difference in the strengths of these pellet systems were thought to be due to changes in the degree of hydrogen bonding within these systems. This work reports the results of studies using magic-angle-spin nuclear magnetic resonance (NMR), x-ray diffraction and degree of crystallinity, and oxygen combustion calorimetry studies of various MCC systems developed to test this hypothesis. Carbon-13 cross polarization magic-angle spin NMR studies of MCC pellets with and without 10% theophylline showed no differences in the spectra of these systems. X-ray diffraction studies and heats of combustion data obtained from oxygen combustion calorimetry of oven-dried pellets of MCC granulated with either water, deuterated water, or a 70/30 ethanol/water mixture were found to have no significant differences in their diffraction patterns, degree of crystallinity, or internal energies. None of these results provide any evidence that a significant net change in the degree of hydrogen bonding is responsible for the observed changes in the strengths of these systems. It is hypothesized that the strength of these dried pellets may, in part, be due to the conversion of some of the intramolecular hydrogen bonded amorphous fibrils at the surface of the MCC particles to intermolecular hydrogen bonded fibrils with other MCC particles.

Five modified numerical deconvolution methods for biopharmaceutics and pharmacokinetics studies

Four improved finite-difference numerical deconvolution methods and one nonlinear regression numerical deconvolution method are proposed and implemented using IMSL/IDLTM. These five numerical deconvolution methods are evaluated using simulated data generated with and without added noise under six different dosing cases. Comparisons between these methods are made in terms of the superimposability of the calculated cumulative amount of drug released or absorbed-time profiles with the theoretical data. The results indicate that the proposed fixed step number equal step length numerical deconvolution method is simple and accurate and therefore is appropriate for pharmacokinetic and biopharmaceutic studies. When an analytic function is legitimate to represent the drug input rate, the nonlinear regression numerical deconvolution method will yield enhanced numerical accuracy and stability.

Calcium antagonists in the elderly. A risk-benefit analysis

Calcium antagonists are effective in lowering blood pressure, relieving anginal symptoms and improving exercise tolerance in older and younger patients with coronary artery disease. Verapamil and diltiazem are effective in slowing ventricular response rates to supraventricular arrhythmias in both older and younger patients. Although they belong to at least 3 distinct chemical classes, a moderate decrease in the clearance of all calcium antagonists occurs with aging. Most clinical trials of these drugs have used the same dosages in older and younger patients, confounding analyses of sensitivity in older compared with younger patients. Greater reductions in blood pressure usually occur in older compared with younger patients receiving the same dosages of calcium antagonists; similarly, the dosage required to reduce blood pressure to a certain level is usually lower in older compared with younger patients. Drug acquisition costs are generally higher for calcium antagonists than for beta-blockers or diuretics. Compared with younger patients, greater heart rate suppression may be seen in older patients treated with verapamil and diltiazem; conversely, heart rate increases are usually seen with dihydropyridines. Calcium antagonists have not been shown to provide long-term benefits or decreased morbidity or mortality in elderly patients with hypertension. Verapamil, but not dihydropyridines, decreases mortality after myocardial infarction in patients without congestive heart failure. Calcium antagonists have not been shown to be beneficial in the treatment of acute stroke. Adverse effects, such as a postural hypotension, may be more frequent in elderly compared with younger patients. In addition, the elderly are at greater risk for drug interactions with calcium antagonists due to the higher likelihood that they are receiving other drugs.

Age and autonomic effects on interrelationships between lung volume and heart rate

To determine effects of aging and autonomic input on interrelationships between respiratory and heart rate variability, we collected 5 min of lung volume of R-R interval data from 7 young [27 +/- 3(SD) yr] and 10 older (69 +/- 6 yr) healthy supine humans before and after double pharmacological autonomic blockade with propranolol (0.2 mg/kg iv) and atropine (0.04 mg/kg iv). Estimates of respiratory and heart rate power spectra and linear transfer functions between the two groups were generated by Fourier analysis. Age, double blockade effects, the age-drug interactions were determined by analysis of variance for repeated measures. Basal R-R intervals were unaffected by age. Double blockade decreased R-R intervals and variability in both age groups (P < 0.0001), but R-R intervals decreased less in older than in young subjects (P < 0.0001). In contrast, basal respiratory intervals and standard deviation were greater in older subjects (P = 0.05) and were unaffected by double blockade in young and older subjects. Lung volume-to-heart rate spectral coherence was highest at frequencies associated with respiration and greater in young than in older subjects (P < 0.07). Double blockade decreased lung volume-to-heart rate variability transfer function magnitude (P < 0.007) and increased phase angle (P < 0.02) without age effects or age-drug interactions. In conclusion, heart rate, respiration, and respiration-heart rate interrelations are altered by aging, and double autonomic pharmacological blockade does not eliminate all age-related differences.

Theophylline controlled-release formulations: in vivo-in vitro correlations

Four experimental controlled-release oral solid dosage formulations were developed and the in vitro dissolution characteristics of theophylline from these formulations were studied in USP apparatus I. Pharmacokinetic evaluation of these formulations was carried out in eight beagle dogs under fasting conditions. Theophylline in a 5% dextrose injection USP, oral solution, and Slo-Phyllin were used as controls to estimate the in vivo dissolution of these four formulations in the GI tract. The percentage cumulative amounts of drug absorbed and the percentage cumulative amounts of drug released into the GI tract from these four controlled-release formulations were obtained by numerical deconvolution methods. The in vivo and in vitro dissolution data demonstrated good correlation indicating that in vitro dissolution tests can be used to optimize the further design of controlled drug release oral solid dosage formulations for theophylline.

Drug release from a multiparticulate pellet system

Multiparticulate pellet systems are used as both immediate and modified release dosage forms. Previous work has classified uncoated pellet systems prepared from microcrystalline cellulose as an inert matrix. The Higuchi square root of time equation, derived to describe drug release from a single planar system, is the accepted method to evaluate drug release from both planar and spherical heterogeneous inert granular matrices. A second equation of interest, the Higuchi cubic equation, was derived to describe drug release from a spherical pellet. Both equations predict a linear relationship between drug release and the square root of time or time. The purpose of the present study was to evaluate drug release from a multiparticulate pellet system using both equations and to study any differences when both equations are used to describe the same drug release data. By evaluating dissolution data from various pellet mesh cuts representing different bead radii and surface areas, changes in the slopes of both plots would be expected. Pellets were manufactured using extrusion/spheronization technology and consisted of 90% microcrystalline cellulose and 10% acetaminophen. Statistical comparison indicates that the Higuchi cubic equation seems to be more sensitive to changes in pellet size. While the square root of time equation describes the drug release data from granular, inert, spherical pellets, it may be better to utilize the Higuchi cubic equation because it is more sensitive to changes in particle size.

Responses to calcium and binding of 3H-nimodipine in the atrioventricular node, atria, and ventricles of mature and old male Fischer 344 rats

To determine whether aging alters cardiac calcium dose responses or dihydropyridine receptor density or affinity, we performed (a) calcium (Ca2+) dose-response studies (3-5 mM) in Langendorff perfused hearts from 12 mature (4-7 month) and 12 old (23-27 month) Fischer 344 rats, and (b) quantitative autoradiography experiments with 3H-nimodipine (50-3,000 pM) in 20-microns tissue sections containing the compact AV node from hearts of eight mature and eight old F344 rats. Baseline AA interval, AV conduction time, AV Wenckebach block cycle length, and QRS duration were prolonged in isolated hearts from old compared with mature rats. In contrast, neither left ventricular developed pressure nor peak dP/dt was altered by age. Perfusion with increasing concentrations of Ca2+ produced decreased coronary perfusion (p < 0.001) without age-related alterations in AA intervals, AV conduction times, dP/dt, or left ventricular developed pressure. No age-related differences in AV node 3H-nimodipine binding (Bmax: mature, 1.35 +/- 0.41 fmol/mm2; old, 1.33 +/- 0.43 fmol/mm2) or affinity (Kd: mature, 915 +/- 375 pM; old, 973 +/- 369 pM) were detected. Similarly, no age-related differences in 3H-nimodipine receptor number or affinity were detected in left and right ventricular or atrial tissue. Total protein in atrial and ventricular tissue was unchanged with age. However, left atrial and left ventricular isolated membrane protein was significantly lower in senescent compared with mature rat hearts (left ventricle: mature, 49.4 +/- 8.7 mg/g; old, 40.9 +/- 3.5 mg/g; p < 0.05; left atria: mature, 36 +/- 9 mg/g; old, 28 +/- 3 mg/g; p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)