Lynda S. Welage

Comparison of Human Duodenum and Caco-2 Gene Expression Profiles for 12,000 Gene Sequences Tags and Correlation with Permeability of 26 Drugs

AbstractPurpose. To compare gene expression profiles and drug permeability differences in Caco-2 cell culture and human duodenum. Methods. Gene expression profiles in Caco-2 cells and human duodenum were determined by GeneChip® analysis. In vivo drug permeability measurements were obtained through single-pass intestinal perfusion in human subjects, and correlated with in vitro Caco-2 transport permeability. Results. GeneChip® analysis determined that 37, 47, and 44 percent of the 12,559 gene sequences were expressed in 4-day and16-day Caco-2 cells and human duodenum, respectively. Comparing human duodenum with Caco-2 cells, more than 1000 sequences were determined to have at least a 5-fold difference in expression. There were 26, 38, and 44 percent of the 443 transporters, channels, and metabolizing enzymes detected in 4-day, 16-day Caco-2 cells, and human duodenum, respectively. More than 70 transporters and metabolizing enzymes exhibited at least a 3-fold difference. The overall coefficient of variability of the 10 human duodenal samples for all expressed sequences was 31% (range 3% to 294%) while that of the expressed transporters and metabolizing enzymes was 33% (range 3% to 87%). The in vivo / in vitro drug permeability measurements correlated well for passively absorbed drugs (R2 = 85%). The permeability correlation for carrier-mediated drugs showed 3- 35-fold higher in human above the correlation of passively absorbed drugs. The 2- 595-fold differences in gene expression levels between the Caco-2 cells and human duodenum correlated with the observed 3- 35-fold difference in permeability correlation between carrier-mediated drugs and passively absorbed drugs. Conclusions. Significant differences in gene expression levels in Caco-2 cells and human duodenum were observed. The observed differences of gene expression levels were consistent with observed differences in carrier mediated drug permeabilities. Gene expression profiling is a valuable new tool for investigating in vitro and in vivo permeability correlation.

Prevention of stress ulceration: current trends in critical care.

Objective:To identify the level of current intensivist’s knowledge regarding risk assessment and intensive care unit (ICU) clinical practice pertaining to stress-related mucosal bleeding, including pharmacologic approaches for stress ulcer prevention. Design:A nationwide survey of critical care physicians. Study Population:Two thousand random physician members of the Society of Critical Care Medicine. Measurements and Main Results:The response rate was 519 (26%) of 2000, with data analysis from 501 (25.1%) usable surveys. Respondents were affiliated with internal medicine (44.3%), surgery (42.3%), and anesthesiology (12.6%). Gut ischemia was indicated as the perceived major cause of stress ulceration (59.7%). The estimated incidence of clinically important bleeding was 2% or less by 62% of respondents; however, 28.6% of physicians surveyed initiate stress ulcer prophylaxis in all ICU patients, regardless of bleeding risk. Respiratory failure was most frequently indicated as a reason for stress ulcer prophylaxis (68.6%), followed by shock/hypotension (49.4%), sepsis (39.4%), and head injury/major neurologic insult (35.2%). The first-line agents selected for stress ulcer prophylaxis include histamine-2 receptor antagonists (63.9%), followed by proton pump inhibitors (23.1%), and sucralfate (12.2%). Concern for nosocomial pneumonia was regarded as more prevalent with antisecretory therapies in those who chose sucralfate (61%) as initial therapy compared with overall respondents (26.9%) (p < .001). Conclusions:The majority of intensivists surveyed recognize stress-related mucosal bleeding as a relatively infrequent event; however, implementation of a stress ulcer prophylaxis risk stratification scheme for ICU patients is necessary. Histamine-2 receptor antagonists are consistently perceived as appropriate initial agents, although proton pump inhibitors have become first-line therapy in an increasing percentage of critical care patients, despite limited data regarding their use in this population.

Human jejunal permeability of cyclosporin A: Influence of surfactants on P-glycoprotein efflux in Caco-2 cells

AbstractPurpose. The purpose of this work was to determine the jejunal permeability of cyclosporin A (CsA) in humans and whether formulation variables modulate the effects of P-glycoprotein (P-gp) on the permeability of CsA in Caco-2 cells. Methods. A solution containing CsA, phenylalanine, propranolol, polyethyleneglycol (PEG) 400, and PEG 4000 was perfused through a 10-cm jejunal segment in 12 subjects. Caco-2 transport studies were performed using previously reported methodology. Results. The mean Peff (±SD) of CsA in humans was 1.65 (0.53). The mean permeabilities for phenylalanine, propranolol, and PEG 400 were 4.54 (2.39), 2.90 (1.28), and 0.83 (0.51) × 10-4 cm/s, respectively. The presence of surfactants significantly decreased the permeabilities of CsA in both directions in Caco-2 cells. Conclusions. The results suggest that the effects of surfactants via micellar solubilization and inhibition of P-gp efflux on CsA transport in Caco-2 cells are significant. CsA can rightly be classified as a low solubility-high permeability Class II BCS drug and its highly variable absorption from Sandimmune® oral formulations is the result of poor dissolution characteristics.

Understanding the scientific issues embedded in the generic drug approval process.

OBJECTIVE To review the major scientific issues embedded in the generic drug approval process. DATA SOURCES Articles indexed initially under terms such as generic medications, generic drugs, bioequivalence, and bioinequivalence. These terms were used to search indexing services such as MEDLINE, International Pharmaceutical Abstracts, CINAHL (a database of nursing and allied health literature), and Science Citation Index. Additional data sources included the Code of Federal Regulations and regulatory guidances from the Food and Drug Administration (FDA) Center for Drug Evaluation and Research. STUDY SELECTION Performed by the authors. DATA EXTRACTION Not applicable. DATA SYNTHESIS Despite the fact that regulations regarding bioequivalence have been in place for more than 20 years, controversies over bioequivalence continue to arise. Consensus on many of these issues is driving the development of new FDA guidances regarding bioequivalence. Still, despite the issuance of new guidance and consensus building among scientists, many clinicians and consumers remain uninformed regarding the scientific basis for establishing bioequivalence and the generic drug approval process in general. Although some have suggested that the generic drug approval process is flawed, overall, it appears that the process works. CONCLUSION Understanding the generic drug approval process and the issues surrounding bioequivalence is of paramount importance to both clinicians and scientists.

Human jejunal permeability of two polar drugs: cimetidine and ranitidine.

AbstractPurpose. To determine the human jejunal permeability of cimetidine and ranitidine using a regional jejunal perfusion approach, and to integrate such determinations with previous efforts to establish a baseline correlation between permeability and fraction dose absorbed in humans for soluble drugs. Methods. A sterile multi-channel perfusion tube, Loc-I-Gut®, was inserted orally and positioned in the proximal region of the jejunum. A solution containing cimetidine or ranitidine and phenylalanine, propranolol, PEG 400, and PEG 4000 was perfused through a 10 cm jejunal segment in 6 and 8 subjects, respectively. Results. The mean Peff (± se) of cimetidine and ranitidine averaged over both phases were 0.30 (0.045) and 0.27 (0.062) × 10−4cm/s, respectively, and the differences between the two were found to be statistically insignificant. The mean permeabilities for propranolol, phenylalanine, and PEG 400 averaged over both phases and studies were 3.88 (0.72), 3.36 (0.50), and 0.56 (0.08) × 10−4 cm/s, respectively. The differences in permeability for a given marker were not significant between phases or between the two studies. Conclusions. The 10-fold lower permeabilities found for cimetidine and ranitidine in this study, compared to propranolol and phenylalanine, appear to be consistent with their less than complete absorption in humans.

Pharmacologic properties of proton pump inhibitors.

Since their introduction into clinical practice in the 1980s, proton pump inhibitors (PPIs) have proved to be of enormous value in the management of acid peptic disorders. They have become the treatment of choice for most, if not all, acid‐related gastrointestinal disorders, including gastroesophageal reflux disease, peptic ulcer, and Zollinger‐Ellison syndrome. With approval of an intravenous formulation, the benefits of PPIs are extended to critically ill patients for whom oral drug administration is often unsuitable. Five PPIs are approved for clinical use in the United States. Although they share a common core structure and mechanism of action, it is important to understand the general pharmacology of these agents and how they differ from histamine2‐receptor antagonists in order to optimize PPI therapy.

Human Intestinal Permeability of Piroxicam, Propranolol, Phenylalanine, and PEG 400 Determined by Jejunal Perfusion

AbstractPurpose. To determine the human jejunal permeabilities of compounds utilizing different transport mechanisms using a regional perfusion approach and to establish a standard procedure for determining drug permeability class to be used for the establishment of drug product bioequivalence standards. Methods. Six healthy male volunteers participated in this study. A multi-lumen perfusion tube was inserted orally and positioned in the proximal region of the jejunum. A solution containing piroxicam, phenylalanine, propranolol, PEG 400 and PEG 4000 was perfused through the intestinal segment at a rate of 3.0 ml/min. Perfusate samples were quantitatively collected every 10 minutes for two 100 minute periods with an intermediate wash out period to determine intra and intersubject variation. Results. The mean Peff (±SD) of piroxicam, phenylalanine, propranolol, and PEG 400 were 10.40 ± 5.93, 6.67 ± 3.42, 3.59 ± 1.60, 0.80 ± 0.46 × 10−4 cm/sec, respectively. The coefficient of variation for the intersubject variability, first and second perfusion periods were: piroxicam, 60.5% and 57.1%; phenylalanine, 52.8% and 57.8%: propranolol, 62.1 % and 44.6%; and PEG 400, 81.7% and 42.3%, indicating a slightly lower CV for the second perfusion period in the same subject. The intrasubject CVs between the two perfusion periods were: 19.4%, 21.3%, 23.6% and 41.0% respectively, indicating a smaller intraindividual variation for all compounds studied. Conclusions. Piroxicam, a nonpolar drug exhibited the highest permeability of the compounds studied. The intrasubject CV was lower than the intersubject CV, indicating consistent permeability estimation within subjects. The methodology is useful for permeability estimation regardless of absorption mechanism and can be used to establish a consistent data base of human permeabilities for estimation of human drug absorption and for establishing the biopharmaceutic permeability class of drugs.

Pharmacokinetics of ceftazidime in patients with renal insufficiency.

The pharmacokinetics of ceftazidime were studied in 14 adult volunteers with different degrees of renal function. The elimination of ceftazidime was totally dependent on renal excretion. The clearance of ceftazidime ranged from 7.5 to 145.1 ml/min and correlated with both renal ceftazidime clearance and creatinine clearance (ClCR). It is recommended that 0.5 to 2.0 g of ceftazidime be given in extended dosages, with intervals dependent on the renal function of the patient. Patients with a ClCR of greater than 50 ml/min should be given ceftazidime every 8 h, those with a ClCR of 30 to 50 ml/min should be given the drug every 12 h, those with a ClCR of 15 to 30 ml/min should be given the drug once a day, and individuals with a ClCR of less than 15 ml/min should be given the drug on a day, and individuals with a ClCR of less than 15 ml/min should be given the drug on a 36- to 48-h regimen.

Variability in cimetidine absorption and plasma double peaks following oral administration in the fasted state in humans: correlation with antral gastric motility

The role of gastrointestinal motility and pH in determining cimetidine bioavailability as well as double peaks in plasma profiles following oral administration, in the quiescent or active phase of antral motility, to humans in the fasted state was examined. Plasma cimetidine-time curves did not show the presence of double peaks in any subject following intravenous administration. The incidence of double peaks was 73% following oral administration and was independent of antral migrating motility complex phase. Further, it was found that oral administration of cimetidine in the quiescent phase resulted in significantly higher bioavailability and in other pharmacokinetic parameters compared to that obtained following administration in the active phase. Excellent linearity in plots of motility peaks vs. plasma peaks with slopes close to unity were evident for both quiescent (r(2)=0.93) and active phase (r(2)=0.97) administration. A total of 14 peaks out of 22 (10 subjects, 64%) and 20 out of 27 peaks (11 subjects, 74%), were accounted for in quiescent and active phase oral administration, respectively. The proximal occurrence of plasma peaks to antral motility peaks typical of phase III contractions strongly implies that motility patterns may be responsible for secondary maxima following oral cimetidine administration in the fasted state.

Comment: Proton Pump Inhibitor Formulary Considerations in the Acutely Ill. Part 1: Pharmacology, Pharmacodynamics, and Available Formulations

Objective: To review important proton pump inhibitor (PPI) pharmacologic, pharmacokinetic, and pharmacodynamic principles in acutely ill patients, compare PPI formulation options for patients unable to swallow a tablet or capsule, and provide clinicians with guidance when making hospital formulary decisions with this class of agents. Data Sources: MEDLINE (1966–May 2005) and the Cochrane Library databases were searched using the key words proton pump inhibitor, acid suppression, peptic ulcer disease, gastrointestinal bleeding, stress ulcer prophylaxis, and critical illness. Bibliographies of cited references were reviewed, and a manual search of abstracts from recent gastroenterology, critical care, and surgery scientific meetings was completed. Study Selection and Data Extraction: All articles identified from the data sources were evaluated, and all information deemed relevant was included for this review. Data Synthesis: PPIs have become a mainstay for acute acid suppression in hospitalized patients over other therapeutic options. Various commercially available PPI products are available for administration, either enterally or parenterally, to patients unable to swallow a tablet or capsule. Newer oral PPI formulations offer numerous advantages over older products. The results of studies comparing the pharmacokinetics and pharmacodynamics of different PPI dosage forms and routes of administration are among the factors to consider when making formulary decisions. CONCLUSIONS: While the introduction of new PPI products has expanded the therapeutic options for acid suppression in acutely ill patients, a number of unresolved questions remain surrounding the interchangeability of these products, the clinical significance of one PPI formulation over the other, and how oral/enteral PPI therapy should be used as step-down therapy after parenteral PPI therapy.