Compilation of Pharmacokinetic Parameters of Beta-Adrenergic Blocking Agents

After defining the drug class of β-adrenergic blocking agents, general aspects for clinical use of β-blockers are discussed, namely absorption, distribution, metabolism, elimination, correlation between clinical response and drug disposition, drug interactions, and influence of disease on drug response and disposition. Pharmacokinetic data for the following β-blockers were retrieved from the literature: acebutolol, alprenolol, atenolol, labetalol, metoprolol, nadolol oxprenolol, penbutolol, pindolol, practolol, propranolol sotalol, talinolol, timolol, and tolamalol. Those pharmacokinetic parameters which were not listed in the original literature were calculated. The use of pharmacokinetic parameters of β-blockers for clinical application is discussed.

Study on Bioavailability of Sulfadiazine Tablets in Man

Sulfadiazine Tablets USP, 500 mg, from 3 different manufacturers were tested in vitro and in vivo. Dissolution rate and disintegration time were measured in water, artificial gastric fluid, and artificial intestinal fluid. Disintegration and dissolution were fastest in artificial gastric fluid. Product I was superior in disintegration to the other two products, whereas product 2 was superior in dissolution. The in vivo study was designed as a Latin square so that each of the 3 treatments was given to each of the 3 subjects at each of the 3 time periods. Two-way analysis of variance was done using the cumulative urinary excretion of free and total sulfadiazine after 24 and 120 hours. Although the extent of bioavailability of product 1 and 2 was only 78 and 73 percent, respectively, statistically significant differences were found only at 24 hours. Judging from both rate and extent of bioavailability, product 3 was superior to products 1 and 2. The difference between in vitro and in vivo data is noted.

Pharmacokinetics of prednisolone in man during acute and chronic exposure to high altitude

INTRODUCTION

The exposure to high altitude (H) produces several physiologic alterations which may induce changes in the pharmacokinetics of drugs. This hypothesis has been confirmed in previous studies which suggest that drugs which are highly bound to plasma proteins are most likely to exhibit altered pharmacokinetics.

OBJECTIVES

To further elucidate the influence of H on pharmacokinetics, prednisolone was selected, since it is highly bound to plasma proteins, renally excreted and poorly bound to red blood cells.

SUBJECTS, MATERIALS AND METHODS

Prednisolone (80 mg) was given orally to three groups of young healthy volunteers. One group was residing at sea level (L): the same volunteers were studied again after 15 hours of exposure to high altitude (3600 m, HA group), and volunteers living at H for at least six months (group HC).

RESULTS

There were no statistically significant differences in the pharmacokinetic parameters calculated from plasma data in the three situations studied. When calculated from whole blood data, however, AUC and Cmax were increased and both volume of distribution and clearance diminished after exposure to H, either acute or chronically. Binding to proteins increased significantly after H exposure from 57% in group L to 75% and 94% in group H and HC, respectively. Binding to erythrocytes also increased with H exposure from 43.7% in group L to 50.6% and 61.6% in group HA and HC, respectively. The prednisolone/prednisone ratio in urine was 11.1 in group L, 7.3 in group HA and 45.6 in group HC.

CONCLUSION

Since prednisone has very little intrinsic glucocorticoid activity and has to be converted to prednisolone for therapeutic effect, the alteration of the prednisolone/prednisone ratio, as a result of high altitude exposure could be clinically relevant. Additional experiments are desirable to further evaluate this observation.

Effects of high altitude exposure on the pharmacokinetics of furosemide in healthy volunteers

INTRODUCTION

A cascade of pathophysiological events occurs with the ascension to high altitude (H). We have performed studies on the effects of exposure to H on the pharmacokinetics of drugs. The hypothesis behind these studies has been that the exposure to H, which produces marked physiological changes in the body, may alter pharmacokinetics, and consequently, pharmacodynamics. Our previous studies suggest that drugs highly bound to plasma proteins are most likely to exhibit altered disposition.

OBJECTIVE

In continuation of our research, we selected furosemide which is about 98% bound to plasma proteins, renally excreted and has low binding to red blood cells.

SUBJECTS, MATERIALS AND METHODS

Furosemide (40 mg) was administered orally to 3 groups of young healthy volunteers. One group who had been residing at sea level (group L), the same group after 15 hours of exposure to high altitude (3,600 m, group HA) and a group of volunteers living at H for at least 6 months (group HC).

RESULTS

Our results are in accordance with the most recent pharmacokinetic studies on furosemide in which a terminal half-life of approximately 20-30 h was reported. Total proteins were 9.3% and 12.7% higher in groups HA and HC, respectively, than in group L. Albumin in group HC was 8.2% higher than group L. Bilirubin increased 17.7% and 41.2% in groups HA and HC, respectively, in comparison with group L. A rapid disposition rate constant in groups HA and HC was the only pharmacokinetic parameter that was significantly different from those in group L. Concentration of furosemide in plasma water increased significantly after H exposure, thus, the binding diminished from 97.2% in group L to 95.1% and 91.1% in groups HA and HC, respectively.

CONCLUSION

Exposure to H produces an increase in the free fraction of furosemide in humans, which could be of therapeutic importance.

Pharmacokinetics of lithium in healthy volunteers after exposure to high altitude

INTRODUCTION

Exposure of the human body to high altitude causes a number of physiological changes. In previous studies, we observed that these changes may alter the pharmacokinetics of drugs. The number of erythrocytes/mm3 increases both, after acute exposure to high altitude (HA), i.e. within 12 - 24 h after reaching high altitude (H), as well as in chronic exposure (HC) (> 10 months) to H. Also binding of drugs to biologic material may change with exposure to HA and/or HC.

OBJECTIVE

Since lithium is transported into and out of erythrocytes and binds strongly to erythrocytes, but is not plasma protein-bound, we selected this drug as candidate for the present study.

SUBJECTS, MATERIAL AND METHODS

Lithium carbonate 300 mg were administered orally to young healthy volunteers. One group residing at low altitude (Santiago, Chile, 600 m, group L), these same volunteers after 15 hours of exposure to high altitude (4,360 m, group HA), and volunteers living at high altitude for at least 10 months (group HC).

RESULTS

We found a significant increase of both hematocrit and red blood cell count (RBC) after exposure to H, both, acute or chronic. Elimination half-life increased 64.1% in group HA and 111.4% in group HC in comparison to group L. We also found an increase in volume of distribution: + 18.9% in group HA, and + 35.8% in group HC when measured in plasma, and + 16.9% in group HA and + 18.8% in group HC when measured in whole blood. Lithium uptake by the erythrocytes increases: the value of 36.7 +/- 22.7% in Group L rose to 54.8 +/- 21.1% and to 54.6 +/- 24.2% in groups HA and HC, respectively. Total clearance decreases at high altitude, though the differences were significant only in group HC (37%).

CONCLUSION

Results indicate that exposure to H produces alterations in the pharmacokinetics of lithium and that these variations may be clinically relevant.

Pharmacokinetics of acetazolamide in healthy volunteers after short- and long-term exposure to high altitude

Exposure to high altitude results in significant physiologic changes and may precipitate mountain sickness, ranging from mild symptoms above 2,500 m to severe symptoms above 4,000 m. In a previous study, changes in the pharmacokinetics of meperidine were observed after exposure to high altitude. This study was conducted to investigate whether similar changes occur for acetazolamide, which is prescribed for prophylaxis of acute mountain sickness. Acetazolamide 250 mg was administered orally to young, healthy male volunteers in groups of 12 each: those residing at sea level (group L), these same volunteers on the day after arrival at high altitude (4,360 m, group HA), and volunteers living at high altitude for 10 months or longer (group HC). Serial blood samples were collected for 24 hours and acetazolamide concentrations were measured in whole blood, plasma, and plasma water. The elimination rate constant (lambda z) was significantly increased in group HA compared with group L. Clearance uncorrected for bioavailability (Cl/F) increased significantly in group HA compared with group L, and further increased in group HC. Apparent volume of distribution (Vz/F) was decreased by 17% in group HA compared with group L, and increased by 37% in group HC compared with group HA. Mean residence time (MRT) was significantly decreased in group HA compared with groups L and HC. Erythrocyte (RBC) uptake increased significantly after a significant increase in RBC count in group HC compared with group L. The extent of protein binding (EPB), however, was significantly decreased in group HA compared with groups L and HC. Free acetazolamide concentrations were significantly lower in group HC than in group L 12 hours after administration. Based on these observations, it is suggested that patients travelling to high altitude, especially altitudes above 4,000 m, should be closely monitored and acetazolamide dosage adjusted as necessary.

Urinary excretion of acetazolamide in healthy volunteers after short- and long-term exposure to high altitude

Acetazolamide is recommended for the prophylaxis of acute mountain sickness symptoms which sets in on climbing to high altitudes (H) above 2,500 m. It is primarily excreted unchanged in urine. In a previous study, we reported on the changes in urinary excretion of meperidine and its metabolite normeperidine on exposure to high altitude. In this study, we investigated the effect on urinary excretion of acetazolamide. The study was carried out in three groups of 12 healthy male volunteers each: at sea level (group L), these same volunteers the day after arrival at high altitude of 4,360 m (group HA), and subjects residing for approximately 10 months at high altitude (group HC). Urine was collected for the periods of 0-2, 2-4, 4-8, 8-12, 12-24 and 24-36 h after peroral administration of a single 250 mg dose. Urinary pH was measured and the concentrations of acetazolamide were determined. There were no significant changes observed in the amount of acetazolamide excreted in urine over 36 h. The urinary pH ranged from 4.5 to 7.8 for L, from 4.2 to 6.9 for HA and from 3.1 to 6.7 for HC. The Fel (fraction eliminated unchanged in urine) was calculated from the amount excreted in 36 h in urine and dose, assuming a bioavailability of 1 based on literature data. No significant changes in Fel were seen.

Animal models for transdermal drug delivery

The purpose of this investigation was to compare the permeation characteristics of two different compounds (extremely polar and nonpolar), i.e., tritium-labeled water (W) and 14C-labeled 7-hydroxycoumarin (7-OHC), among 16 different species, including human skin. Snake skin exhibited highest permeability for both W and 7-OHC. Permeability and lag time values of W and 7-OHC across Brattleboro rat and hairless guinea pig are very close to human skin. Skin thickness in micrometers (full thickness, epidermis and stratum corneum, and stratum corneum), and number of hair follicles present in each cm2 were determined for each species. There was no relationship between number of hair follicles and permeability values for both W and 7-OHC. The skin thickness (full) was related to the relative permeability values of W, whereas for 7-OHC it was not.

The effects of triethanolamine myristate, a fatty acid salt, on the availability of riboflavin in humans

A human study examined the effect of administering a triethanolamine myristate tablet 30 min prior to or concomitantly with a fast release riboflavin tablet and a slow release riboflavin tablet. There was no significant difference between any of the treatments although treatments with the slow release riboflavin resulted in greater urinary excretion of riboflavin. It is possible that a difference may only be seen within subjects because gastric emptying has a large intraindividual variation. When triethanolamine myristate is administered to delay gastric emptying, the inhibition may be affected by the individual's normal transit rate. Another reason-might be lack of sufficient bile salts in the fasting state, reducing chyme and micelle formation, or a higher dose of triethanolamine myristate may have been needed to detect a difference.

The effects of triethanolamine myristate, a fatty acid salt, on the bioavailability of riboflavin in dogs

A study in dogs was performed in which a physiologic approach to delaying gastric emptying was examined. Triethanolamine myristate (a fatty acid salt) was used to delay gastric emptying in hopes of increasing the bioavailability of riboflavin. A bilayer tablet consisting of triethanolamine myristate and riboflavin resulted in an absolute bioavailability of 2-3 times greater than the bioavailability of riboflavin alone. Increases in bioavailability although to a lesser extent, were also seen with the 30 min pretreatment with triethanolamine myristate. The results suggest that it was possible to delay gastric emptying.

Microemulsion technology in the reformulation of cyclosporine: the reason behind the pharmacokinetic properties of Neoral

Management of transplant patients receiving cyclosporine therapy is complicated by interpatient and intrapatient variability in pharmacokinetic parameters caused by the drug's unpredictable bioavailability. Cyclosporine, a highly lipophilic cyclic polypeptide, has recently been reformulated using a microemulsion delivery system to improve its bioavailability. This new orally administered formulation, Neoral (cyclosporine capsules and oral solution for microemulsion), has self-emulsifying properties and spontaneously forms a microemulsion (particle size < 0.15 microns) in the aqueous fluids of the gastrointestinal tract. Clinical trials in renal transplant recipients, liver transplant recipients with external biliary diversion, and healthy volunteers have demonstrated enhanced bioavailability and greatly improved dose linearity with the cyclosporine microemulsion compared with the original cyclosporine formulation, Sandimmune (cyclosporine). The rate and extent of absorption were greater with the cyclosporine microemulsion under both fasting and nonfasting conditions, and there was a more consistent relationship between the administered dose and area under the time-concentration curve. Early clinical efficacy trials in renal and liver transplant recipients have shown no difference in the incidence or severity of drug-related adverse events. Studies on the long-term efficacy and safety of the new microemulsion formulation are ongoing.

Pharmacokinetics of meperidine in healthy volunteers after short- and long-term exposure to high altitude

Increased numbers of erythrocytes have been shown ex vivo to increase meperidine uptake, and one of the major physiologic changes that occurs at high altitude is an increase in hematocrit and erythrocytes. A study was therefore conducted to evaluate the effects of high altitude on the pharmacokinetics of meperidine. Intramuscular doses (0.75 mg/kg) of meperidine were given to three groups of healthy volunteers (age range, 18-20 years): participants living at sea level (group L), those same participants the day after arrival at high altitude (4,360 m; group HA), and participants who had lived at high altitude for > or = 10 months (group HC). Blood samples were collected for 12 hours after drug administration. Meperidine was measured in whole blood, plasma, and plasma water. Elimination rate constant (lambda z) and clearance uncorrected for bioavailability (Cl/F) were significantly lower at high altitudes than at sea level in plasma (HA and HC) and in whole blood (HA only). Mean residence time (MRT) was significantly higher at high altitudes than at sea level in plasma (HA and HC) and in whole blood (HA only). Hematocrit was significantly increased at both time points at high altitude in comparison to values at sea level, and was also higher after a long-term stay at high altitude than after arrival at high altitude. Erythrocyte binding increased significantly from 41.3% at sea level to 43.8% at arrival at high altitude to 50.9% after a long-term stay at high altitude. The extent of protein binding tended to decrease with high altitude, but this decrease was not significant. Free concentrations of meperidine in plasma water measured 1, 2, and 4 hours after administration were significantly increased after 2 and 4 hours.

Pharmacokinetics of melatonin in human sexual maturation

To determine whether melatonin pharmacokinetics change during puberty, we infused melatonin iv in 9 prepubertal, 8 pubertal, and 16 adult subjects and measured melatonin in serum and saliva, and 6-hydroxymelatonin sulfate in urine. A pilot study of 3 adult males showed dose linearity, absence of saturation kinetics, and unaltered metabolism and urinary excretion for doses of 0.1, 0.5, and 5.0 micrograms/kg. All other subjects received 0.5 microgram/kg melatonin. The results of pharmacokinetic parameters calculated from serum melatonin showed no significant gender differences in adults. However, developmental differences were significant between prepubertal children and adults for terminal elimination rate constant (1.08 +/- 0.25 vs. 0.89 +/- 0.11 h-1), elimination half-life (0.67 +/- 0.12 vs. 0.79 +/- 0.10 h), and area under the concentration-time curve (250.9 +/- 91.8 vs. 376.9 +/- 154.3 (pg/mL).h, respectively). At all time points melatonin levels were higher in serum than in saliva, and the ratio between serum and salivary melatonin varied up to 55-fold within and between individuals. Results based on salivary melatonin showed significant differences between prepubertal children and adults for the terminal elimination rate constant (1.90 +/- 0.95 vs. 1.06 +/- 0.28 h-1). The described group differences in pharmacokinetic parameters suggest that prepubertal children metabolize melatonin faster than adults. The inconsistent ratio between serum and salivary melatonin calls for caution in the use of salivary melatonin for pharmacokinetic studies or to infer pineal function. The present findings, suggestive of faster melatonin metabolism in prepubertal children, combined with the known decline of serum melatonin with age and higher excretion rate of the metabolite in prepubertal children lead us to conclude that the prepubertal pineal gland has a higher melatonin secretion rate than the adult gland.

Urinary excretion of meperidine and normeperidine in man upon acute and chronic exposure to high altitude

The urinary excretion of unchanged meperidine (M) varies with change of pH and metabolism. Since exposure of man to high altitude (H) may cause significant physiologic changes, we investigated its effects on the urinary excretion of M. The study was carried out in 3 groups of healthy, male volunteers (ages 18-20 years): at sea level (L), at 4360 m the day after arrival at H (HA), and at 4360 m in subjects residing for > 10 months at H (HC). Urine was collected for the periods of 0-4, 4-8, 8-12 and 12-24 h. Urinary pH was measured and the concentrations of M and normeperidine (N) were determined. The 24 h excretion of M and N was significantly decreased for L vs. HA and L vs. HC. Significance was also seen for the periods 0-4, 4-8 and 8-12 h. The ratio of amount excreted M/N for the 24 h period was highly significant for L vs. HA and L vs. HC. The urinary pH ranged from 5.3-5.9 for L, 5.9-7.0 for HA, and 5.1-5.7 for HC. The Fel (fraction of M eliminated in the unchanged form in urine) significantly decreased from L to HA and HC.

Application of neural networks for the prediction of human pharmacokinetic parameters

Artificial neural network (ANN) is a method used in the prediction of response variables from a set of input and target parameters. The most commonly used network in the area of pattern recognition is the feed forward/back propagation (BPN) network. A method to predict human pharmacokinetic parameters has been proposed using BPN with a combination of physicochemical properties and animal pharmacokinetic parameters. The results were compared with in vitro estimation of the same pharmacokinetic parameters. Fourteen network models, using a variety of input variables, were developed. Protein binding, partition coefficients, dissociation constants, and the total clearance (Cltot) and volume of distribution (Vz) in rat and dog species of 41 drugs were evaluated for prediction of human total clearance and volume of distribution using the EDBD algorithm. The observations showed highest prediction for Cltot and Vz when rat and dog pharmacokinetics, combined with protein binding and partition coefficients of the drugs, were used as input parameters. Drugs with a partition coefficient (log P) < 1.17 showed predictability of 63.41% for Cltot and 48.78% for Vz. Drugs with low protein binding (approximately 20%) showed predictability of 19.51% for Cltot and 41.46% for Vz. Comparison with in vitro estimation showed no bias in the prediction of either clearance (p < 0.2) or volume of distribution (p < 0.5) by the two methods.

Meperidine uptake and binding to human blood ex vivo

Many drugs are bound to plasma proteins (PR) and/or to erythrocytes (RBC). The RBC count may change due to physiologic factors such as exposure to high altitude, or pathologic conditions such as anemia or as consequence of cancer treatment. The purpose of the investigation was to study the influence of 1) drug concentration, and 2) number of RBC on erythrocyte uptake or binding using meperidine as a model drug (M). Human RBC concentrated blood was used and blood chemistry determined. Using human plasma (P) dilutions were made containing 9.9, 7.62, 5.87 and 4.11 million RBC mm3. The whole blood (WB) samples were spiked with M to result in 10, 25, 50, or 75 micrograms/ml. Increasing concentrations of M within each group of same RBC count did not influence percentage of erythrocyte uptake/binding. Increase in RBC count from 4.11 to 9.9 million/mm3 resulted in significant increase in erythrocyte uptake from 77.1% to 94.7% and increase in PR binding from 37.2% to 87.4%.

A biopharmaceutic approach in designing a controlled release tablet of sodium monofluorophosphate: 1. In vitro and in vivo studies in beagle dogs

The purpose of this study was to develop a controlled release tablet (CRT) of sodium monofluorophosphate (NaMFP) based on biopharmaceutic and pharmacokinetic principles. NaMFP was introduced in the early eighties to treat osteoporosis. The required dose size (200 mg of NaMFP) and time of drug delivery (8.3 h) were theoretically determined based on the pharmacokinetic parameters of fluoride (F-). A CRT was formulated with ethyl cellulose (EC) by the direct compression method. The ratio of drug to polymer was adjusted 1:1, after studying the in vitro release profiles. The release mechanism from the developed dosage form followed the square root of time relationship. This dosage form was evaluated for its in vivo performance in dogs. The pharmacokinetics of F-, after the IV and PO administration of NaMFP, was determined to standardize the animal model. F- followed a two-compartment model and no significant differences were found between the two routes of administration. The bioavailability in dogs was only 60%. The reason for this poor bioavailability was postulated to be the delivery of drug extended beyond the principal sites of absorption of the gastrointestinal tract. Hence, we decided to characterize the absorption sites of NaMFP and to modify the CRT.

Biopharmaceutic approach in designing a controlled release tablet of sodium monofluoro phosphate. Characterization of absorption sites and evaluation of modified dosage form

Based on the results from in vivo study in dogs, it was decided to characterize the absorption sites of sodium monofluoro phosphate (NaMFP). It was hypothesized that bioavailability upon p.o. administration can be improved for controlled release dosage forms if the drug release is confined to segments of gastrointestinal tract responsible for absorption. To characterize the principal sites of absorption of NaMFP, in situ segmental absorption studies were carried out in rats. It was found that NaMFP is predominantly absorbed from the small intestine. The larger surface area and presence of alkaline phosphatase enzymes, are attributed to the higher absorption from the small intestine. Based on these results the delivery time was limited to 6 h to restrict the release of the drug within the principal sites of absorption. The dose was adjusted to 160 mg of NaMFP. After studying in vitro release profiles, the drug to polymer ratio was adjusted to 1: 1.1. The modified dosage form was finally subjected to bioavailability studies in humans. An immediate release dosage form was used to compare the efficacy in a two-period crossover study. The extent of bioavailability was 99% and the dosage form was effective in reducing the fluctuations.

Introduction to gene technology

The increased use of biotechnology for numerous categories of common products (pharmaceuticals, foods, agricultural chemicals, etc.) has an ever increasing impact on our society. In the medical/pharmaceutical field, biotechnology signifies a drastic change in the approach to drug discovery, research and development, diagnosis, and disease management. The basis of replication, transcription, translation, recombinant DNA technology, and production of altered genes are defined. Examples of biopharmaceuticals, i.e., enzymes or regulators of enzyme activity, hormones or hormone-like growth factors, cytokines, vaccines, monoclonal antibodies, and gene transfer in humans are discussed.

Development of an azopolymer based colonic release capsule for delivering proteins/macromolecules

The colon, high in microbial contents with degradation ability of azo bonds, seems to be suitable for site-specific delivery of drugs. The degradation of azoaromatic hydrogel depends on the degree of swelling. However, the degree of swelling of azopolymers and the ability of the azoaromatic polymers to protect peptide drugs against the action of digestive enzymes still remains to be established. An azopolymer was synthesized and membranes were cast to investigate the degree of swelling. An azopolymer-coated capsule suitable for delivering peptides/proteins to the colon was developed by in vitro evaluation using vitamin B12 as a model drug to screen various formulations. For in vitro dissolution the half-changed method was used to mimic the pH-time profile in the GI tract. It was shown that the release of vitamin B12 is dependent on the degree of swelling which increases as pH increases. An in vivo study was also performed with insulin in azopolymer-coated capsules in 6 normal beagle dogs. The results suggest that this azopolymer-coated capsule is capable of protecting peptide/macromolecules against digestive enzymes. However, to obtain a promising peroral insulin capsule, more formulation work is required to achieve better absorption availability.

Development and evaluation of a monolithic floating dosage form for furosemide

The poor bioavailability of orally dosed furosemide (60%), a weakly acidic drug, is due to the presence of a biological window comprised of the upper gastrointestinal tract. The purpose of the present study was to develop and optimize in vitro a monolithic modified-release dosage form (MMR) for furosemide with increased gastric residence time and to evaluate the in vivo performance of the dosage form. The principle of floatation was used to restrict the MMR to the stomach. A two-factor three-level full factorial experimental design was employed for formulation development. A flow-through cell was designed to evaluate in vitro dissolution parameters. Quadratic regression models indicated the polymer viscosity and polymer:drug ratio to be significant (p < 0.05) formulation factors in determining the duration of buoyancy and the release profile. Statistical optimization using response surface methodology with certain physiological constraints relating to gastric emptying time predicted an optimal MMR. In vivo evaluation of the optimized MMR in beagle dogs resulted in a significant increase (p < 0.05) in the absolute bioavailability for the MMR dosage form (42.9%) as compared to the commercially available tablet (33.4%) and enteric product (29.5%). Significant in vitro/in vivo correlations (p < 0.05) were obtained for the MMR using deconvolution analysis normalized for bioavailability. The floating dosage form was found to be a feasible approach in delivering furosemide to the upper gastrointestinal tract to maximize drug absorption.

Chronopharmacology: a review of drugs studied

The science dealing with the phenomenon of rhythmicity in living organisms is called chronobiology. The branch dealing with the pharmacologic aspects of chronobiology is termed chronopharmacology, which may be subdivided into chronotherapy, chronopharmacokinetics and chronotoxicity. After a short discussion of the terminology used in chronobiology, a survey of drugs studied with respect to chronopharmacology, particularly of chronopharmacokinetics in man, is given.

Gastrointestinal parameters that influence oral medications

The successful functioning of oral medication depends primarily on how the gastrointestinal (Gl) tract processes drugs and drug delivery systems. Parameters such as regional pH, motility (and hence residence time), and brush border and colonic microflora enzymatic activity play an important role in the performance of orally administered dosage forms. In addition, medications are required to treat disease states that alter normal functions of the body. This review (which summarizes the symposium of the same title undertaken in the 2nd Jerusalem Conference on Pharmaceutical Sciences and Clinical Pharmacology, Jerusalem, Israel, May 1992) focuses on two aspects: (1) how some physiological parameters of the intestine can be manipulated to achieve control over drug absorption (P. Bass: alteration of the paracellular space of enterocytes with glucose to modulate the passive movement of drugs; E. Ziv: intestinal absorption of insulin) and spatial placement of drugs (D.R. Friend: use of colonic beta-glucosidases to target glycoside prodrugs of steroids to the large bowel; A. Rubinstein: specific degradation of polysaccharide matrices by colonic bacteria); and (2) how abnormalities of the Gl tract affect drug performance (J.B. Dressman: physiological and pathophysiological changes in upper Gl tract pH may lead to alterations in drug bioavailability; W. A. Ritschel: influence of diseases on the pharmacokinetics of drugs).

Disposition characteristics of coumarin as a function of age in the beagle dog model

Coumarin (C, CAS 91-64-5) is a high extraction ratio drug, and its clearance reflects the liver blood flow. The purpose of this study was to investigate the alterations in the pharmacokinetics of C as a function of age, and to evaluate the suitability of beagle dog model to study age dependent changes in the hepatic function. In this longitudinal study, C was administered intravenously to male beagle dogs, ranging in age from < 1 to 15 years. The total clearance decreased significantly from 30.67 +/- 9.58 to 16.61 +/- 2.35 ml/min/kg and the ratio of AUC of glucuronide metabolite to parent drug decreased from 1.26 +/- 0.52 to 0.72 +/- 0.17 in old dogs. No significant changes were observed in apparent volume of distribution and elimination half-life. The changes in clearance of C parallels the observed reduction in the liver blood flow in man, suggesting that the beagle dog appears to be a good model for drug disposition studies in gerontokinetics.

Multiple-layer, direct-compression, controlled-release system: in vitro and in vivo evaluation

A new approach to achieve controlled drug delivery is demonstrated for a triple-layer tablet, which simultaneously combines the principles of diffusion and dissolution. Heckel's equation was used to characterize the compression behavior of formulation components. A balanced proportion of each component and a model drug (theophylline) were selected to avoid lamination after ejection and ensure coherent compaction. In vitro release profiles over a period of 10 h in different dissolution media and hydrodynamic conditions were similar and resulted in an n value of 0.786, signifying anomalous release kinetics. The n value is calculated from a curve fit to the empirical equation: Mt/Minfinity = Ktn, where Mt and Minfinity denote the amount of drug released at time t and at infinite time, respectively, K denotes the proportionality constant, and n characterizes the type of release mechanism operative during the dissolution process. In vivo study in human subjects after administration of the experimental triple-layer system exhibited a steady rise in plasma concentration up to 7 h. The actual amount of drug absorbed by the body was calculated by the Wagner-Nelson technique, and a linear relationship was observed between the percentage absorbed in vivo and the percentage dissolved in vitro. The proposed triple-layer model appears to provide good correlation between in vitro and in vivo results with maximum flexibility with respect of dose, duration range, and ease of production.

Standards of clinical investigations in the USA

The drug approval process in the USA is under constant surveillance, monitoring and evaluation. Several significant changes were made during the past few years and many others are under consideration. The FDA has undergone organizational changes, which together with the IND Rewrite and NDA Rewrite resulted in a shift of emphasis in clinical studies.

The allometric approach for interspecies scaling of pharmacokinetic parameters

A long standing problem in pharmacokinetics and toxicology is the extrapolation and correlation between results obtained in different animal species and man. Animal data may be scaled-up to predict PPs in man using the allometric approach. The allometric approach is empirical, but easy, and is based on the fact that the underlying physiological processes such as blood flow, heartbeat duration, breath duration etc. are essentially physical and related to B. This approach is generally applicable to compounds that are essentially renally excreted. For substances that are highly extracted by the liver, Cltot is a function of the LBF among various species. Based on the concept of neoteny, use of brain weight affords a more correct approach to the scaling of Cl(int) of low extraction ratio drugs. By using the invariant pharmacokinetic time, the superficial differences in concentration-time profiles due to chronological time among different species are removed. Finally, as Boxenbaum (1984) has said "parameters to be scaled, independent variables, and the mathematical relationships used in the scaling process are all at the discretion of the investigator. There are no proper or improper approaches; the only limitations are those imposed by the investigator."

Identification of populations at risk in drug testing and therapy: application to elderly patients

Risks associated with drug therapy are more prevalent with advancing age. In drug evaluation it is imperative to identify risk groups. Six strategies are discussed to identify risk groups: (a) from physico-chemical, preclinical drug data, and expected physiologic changes; (b) from animal and human phase I PK data and expected physiologic changes; (c) from epidemiologic data and expected physiological changes; (d) from animal/human toxicokinetic data and expected physiologic changes; (e) from retrospective patient monitoring; (f) from population kinetics using NONMEM; and (g) from pharmacokinetic screen approach.

Prediction of the volume of distribution of 7-hydroxycoumarin in man from in vitro and ex vivo data obtained in rat

The essential parameter to estimate the first dose size of a drug in man is the volume of distribution. For a drug that has never been used in man before, estimates of the volume of distribution can only be obtained from animals and in vitro data. The purpose of this study was to compare various approaches presented in the literature for predicting the volume of distribution at steady state (VSS) and the terminal phase volume of distribution (Vd beta) in man. A lipophilic active metabolite of coumarin, 7-hydroxycoumarin (7OHC), was selected for this investigation. This compound is extensively metabolized in both the central and peripheral compartments. Of the six methods evaluated, only an empirical allometric approach yielded a reasonable estimate of VSS. All methods underestimated VSS and none of the applicable methods were able to predict Vd beta. The reason for this discrepancy may be due to the fact that the calculation of VSS in man was done assuming elimination from the central compartment.

Pharmacokinetics and bioavailability of papaverine HCl after intravenous, intracorporeal and penis topical administration in beagle dogs

Bioavailability and pharmacokinetics of papaverine HCl was studied in beagle dogs following intravenous injection, intracorporeal injection and topically applied gel on the penis. Also the effect of the sorption promoter Labrafil M-1944 CS on the permeation of papaverine from two gel formulations (PT and PTL) containing the co-solvent Transcutol was evaluated. Blood samples were analyzed by high performance liquid chromatography (HPLC). The pharmacokinetic parameters were determined using either curve-fitting (RE-SID) or compartment model independent method (AUC-RPP). The plasma concentration-time profiles show that papaverine HCl pharmacokinetics is best described by an open two-compartment model. The absolute bioavailability of papaverine HCl was determined to be 102.4%, 9.1%, and 12.4%, respectively, following intracorporeal injection, gel PT and gel PTL administration.

Development of a colonic release capsule dosage form and the absorption of insulin

Since the colon is relatively low in peptidase activity and drainage into the lymphatics is maximized, a peroral dosage form was developed to deliver insulin to the colon. Microemulsions, used as a vehicle for insulin, were gelled using Cab-O-Sil, and filled into gelatin capsules pretreated with formaldehyde vapor. The capsules were coated with Eudragit NE 30 D, Eudragit S100 and cellulose acetate phthalate polymers of pH-dependent and time-controlled release mechanisms. In vitro dissolution profiles of the capsule coating, using sodium salicylate as the marker, show that dissolution of the capsule begins at 4 h, at pH 5.5, and is completed at 8 h, at pH 7.7, simulating the gastrointestinal transit and pH profile of the dog. An in vivo crossover study in beagle dogs was carried out employing the following treatments: i.v. insulin, p.o. insulin microemulsion and colonic release capsule dosage form without insulin (CRC), were used as controls, a colonic release capsule dosage form with insulin (CRI) and additionally with sodium laurylsulfate (CRIL) or aprotinin (CRIA) as sorption promoter and enzyme inhibitor, respectively. Evaluation was done by measuring the reduction in blood glucose concentration levels. The pharmacological availability (P.A.) is the ratio of the area under the baseline curve (AUC), expressed as percent glucose reduction from baseline vs time, of the p.o. dosage forms to i.v. insulin administration, corrected for body weight and dose size. The P.A. for the p.o. microemulsion, CRC, CRI, CRIL and CRIA were 2.1, 0.4, 5.0, 2.7 and 6.2%, respectively. Insulin release occurred throughout the GI tract, with the exception of the stomach. Tmax occurred at 6.4 h for CRIA; the majority of insulin is taken up after the colonic arrival time is reached in the dog (4-6 h). Duration of the reduction in blood glucose levels occurred for 14 h with the CRIA dosage form.