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  • 1
    Electronic Resource
    Electronic Resource
    Evaluation of the absorption from some commercial sustained-release theophylline products (1980)
    Springer
    Journal of pharmacokinetics and pharmacodynamics 8 (1980), S. 131-149 
    Details
    ISSN: 1573-8744
    Keywords: theophylline ; absorption ; bioavailability ; sustained release ; tablets ; plasma concentrations ; mean plasma concentrations ; steady-state projections
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Absorption of theophylline from three commercial products labeled as sustained release was compared to the absorption from a standard uncoated tablet (Searle 200-mg aminophylline tablet) in a single-dose study. Aminodur tablets (Cooper) and Slophyllin Gyrocap capsules (Dooner) had bioavailability (100.2%±19.8% and 98.5%±13.8%) statistically indistinguishable from that of the standard but showed significantly slower absorption (peak times of 10,4±2.8 and 4.36±1.35 hr) and lower peak plasma concentrations (13.9±4.5 and 22.6±3.5gmg/ml/g dose) than the standard (t peak ,1.52±0.45 hr; Cpeak,28.l±6.2μg/ml/g dose). The time of the plasma concentration peak (2.47±1.38 hr) after a dose of Tedral S.A. (Warner/Chilcott) was not statistically different from that after the standard, but both the peak concentration (16.0±3.9 gmg/ml/g dose) and bioavailability (76.0±18.4%) were. Multiple-dose projections from single-dose data indicate that of the three test products only Aminodur maintains reasonably constant interdose plasma levels during 12 hourly dosing. With an 8 hourly dosing schedule Gyrocaps also might be satisfactory. Reasonable predictions of the plasma concentrations arising from Aminodur doses have been made using a single-compartment body model and assuming input from an outer followed by an inner layer of the tablet. Typically a single dose of a preparation designed for constant release of drug over 12 hr should not produce a plasma concentration plateau in subjects with an average 6.1-hr drug half-life. The apparent plateau in the mean plasma profile (i.e., concentrations at each sampling time averaged over all subjects) for Aminodur doses is evaluated. The interpretation commonly being implied in the publication of mean profiles from bioavailability studies is misleading, particularly when applied to sustained-release preparations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01065189
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  • 2
    Electronic Resource
    Electronic Resource
    Evaluation of the absorption from some commercial enteric-release theophylline products (1980)
    Springer
    Journal of pharmacokinetics and pharmacodynamics 8 (1980), S. 151-164 
    Details
    ISSN: 1573-8744
    Keywords: theophylline ; absorption ; bioavailability ; enteric release ; tablets ; plasma concentrations ; dissolution data
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract In a single-dose bioavailability study, Wales, Robinson, Columbia, and Choledyl (Warner/Chilcott) enteric-coated tablets all allowed a bioavailability of theophylline (99%±25%, 102%±23%,103%±18%, and 98%±15%;mean±SD, n=12) statistically indistinguishable from that of the standard uncoated tablet (Searle 200 mg aminophylline). Only the Wales and Choledyl tablets (7.6, 4.2 hr) could be shown (p〈0.05) to generate a peak plasma theophylline concentration later than the standard (1.4 hr). All tablet brands demonstrated a significant lag time before appearance of theophylline in the plasma, and both Wales and Choledyl tablets also had a (t peak -t tag )statistically different from that of the standard. Despite misleading indications from the mean plasma profile (plasma concentrations at each sampling time averaged over all subjects), plasma data from the individual participants and in vitrodissolution data show that, while release of theophylline from the Wales tablet might be inordinately slow, this is not a sustained-release preparation. Of the enteric-coated tablets only the Columbia product allowed significant levels in the first sample after dosage. Five of the 18 Columbia doses gave rise to 40–99%of the peak concentration in the 1- hr sample. In vitro,it takes 39±14 min for 40% of the theophylline content of Columbia tablets to dissolve in simulated intestinal fluid. Surprisingly rapid delivery of an entericcoated tablet to the duodenum would appear to be required to allow a significant percentage of theophylline to be dissolved and absorbed before 1 hr. None of 12 Columbia tablets tested in vitro,however, allowed dissolution of more than 0.2% of their theophylline content during 1 hr immersion in simulated gastric fluid. Since once in intestinal fluid Columbia tablets appear to dissolve more rapidly than the other enteric products, it is not clear whether the five Columbia tablets in question had imperfections or whether, in fact, this tablet brand more closely than the others represents the ideal of immediate release once in the duodenum. Plasma samples should be taken as early as 15 min after dosage when evaluating the bioavailability of enteric release products.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01065190
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  • 3
    Electronic Resource
    Electronic Resource
    Evaluation of the absorption from 15 commercial theophylline products indicating deficiencies in currently applied bioavailability criteria (1980)
    Springer
    Journal of pharmacokinetics and pharmacodynamics 8 (1980), S. 229-242 
    Details
    ISSN: 1573-8744
    Keywords: theophylline ; absorption ; tablets ; oral solution ; intravenous ; bioavailability criteria
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The biovailability of theophylline from alcoholic and aqueous oral solutions was compared to that from an intravenous dose in 12 normal adults. The alcoholic elixir surprisingly gave rise to a significantly greater (114 ±14%, mean±sd amount absorbed than did the intravenous dose. The aqueous solution (99±8%) and intravenous dose were statistically indistinguishable in this respect, and, furthermore, the extent of absorption from a 300-mg dose of the aqueous solution was 99±10% of that from a 500-mg dose, and not statistically different. The aqueous solution was thus employed in three subsequent studies as a standard with which to compare 13 different types of theophylline tablets, all marketed in the United States. Of the 13 tablets, eight showed bioavailability statistically distinguishable from that of the standard. Nevertheless, for only two tablets could it be claimed with 95% confidence that the bioavailability was less than 95%. For none can it be stated at this confidence level that the bioavailability is less than 90%. Bioavailability studies should include criteria of clinical significance in addition to criteria of statistical significance. Contrary to the usual rationale behind choice of a bioavailability standard, nine of the 12 uncoated tablets appeared to allow more rapid absorption of theophylline than did the standard oral solution, an aqueous syrup. Increasing the dose of syrup decreased the rate of theophylline absorption. Orally administered drug solutions may have properties more absorption rate limiting than the disintegration of many brands of tablet.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01059644
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  • 4
    Electronic Resource
    Electronic Resource
    Sumatriptan Absorption from Different Regions of the Human Gastrointestinal Tract (1995)
    Springer
    Pharmaceutical research 12 (1995), S. 138-143 
    Details
    ISSN: 1573-904X
    Keywords: sumatriptan ; gastrointestinal tract ; absorption ; metabolism ; pharmacokinetics
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Sumatriptan exhibits low oral bioavailability partly due to presystemic metabolism, which may vary with regional differences in metabolic activity throughout the gastrointestinal tract. This study evaluated sumatriptan absorption in humans after administration orally and by oroenteric tube into the jejunum and cecum. Because the site of cecal administration varied, pharmacokinetic parameters for sumatriptan and its major metabolite were compared statistically only after oral and jejunal administration. One-half of the oral dose was recovered in the urine as parent (3%) and metabolite (46%). Sumatriptan was absorbed throughout the gastrointestinal tract; absorption was similar after oral and jejunal administration, and less after cecal administration. The metabolite AUC and the AUC ratio (metabolite/parent) were significantly lower after jejunal compared to oral administration; the AUC ratio was two-fold lower after cecal administration. Results suggest that presystemic metabolism of sumatriptan varies throughout the gastrointestinal tract and/or regional differences exist in the absorption of metabolite formed within the gastrointestinal tract.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1016211409315
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  • 5
    Electronic Resource
    Electronic Resource
    Effect of Sodium Acid Pyrophosphate on Ranitidine Bioavailability and Gastrointestinal Transit Time (1993)
    Springer
    Pharmaceutical research 10 (1993), S. 1027-1030 
    Details
    ISSN: 1573-904X
    Keywords: ranitidine ; effervescent tablet ; absorption ; bioavailability ; bioequivalence ; sodium acid pyrophosphate ; gastrointestinal transit time
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract During development of a ranitidine effervescent oral solution dosage form, a marked decrease was observed in the extent of ranitidine absorption relative to the conventional oral tablet. Two studies were conducted in healthy volunteers to confirm the involvement of an excipient, SAPP (sodium acid pyrophosphate), and the mechanism of interaction, altered gastrointestinal transit. The first study (n = 12) involved single-dose crossover comparisons of (A) 150 mg ranitidine with 1132 mg SAPP versus (B) 150 mg ranitidine and (C) 150 mg ranitidine with all the effervescent tablet excipients except SAPP versus (D) a 150-mg ranitidine effervescent tablet, all administered as oral solutions. Serum ranitidine AUC, C max, and t max were compared using two one-sided t test 90% confidence intervals (CI). Comparing treatments A to B and D to C, all 90% CI were below the 80–120% range, indicating significantly less extensive ranitidine absorption (54% based on AUC) from the oral solutions containing SAPP. The second study (n = 12) was a single-dose crossover comparing 50 µCi 111InCl solutions with and without 1132 mg SAPP. Gastrointestinal transit times, determined by scintigraphic imaging, were compared between treatments. Gastric emptying time was unchanged, but small intestinal transit time was decreased to 56% in the presence of SAPP. More rapid small intestinal transit associated with an excipient of a solution dosage form apparently resulted in a decreased extent of ranitidine absorption. This observation contradicts the conventional wisdom that oral solutions are unlikely to fall short of bioequivalence relative to solid oral formulations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018918907670
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  • 6
    Electronic Resource
    Electronic Resource
    Intraindividual variability in theophylline pharmacokinetics: Statistical verification in 39 of 60 healthy young adults (1982)
    Springer
    Journal of pharmacokinetics and pharmacodynamics 10 (1982), S. 123-134 
    Details
    ISSN: 1573-8744
    Keywords: theophylline ; pharmacokinetics ; variability ; disposition rate constant ; man
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract After administering a single 300 mg dose of theophylline in oral solution to 12 healthy adults, the dose-normalized area under the plasma concentration-time curve was 97.2±20.1 % (mean±SD) of that after giving a 500 mg dose and statistically indistinguishable. Similarly, these areas multiplied by the individual's terminal disposition rate constant (β) were statistically indistinguishable between 300 and 500mg doses (99.1±10.3%), giving no evidence of dose-dependence for theophylline kinetics at the levels below 15 μg/ml observed in these individuals. After an intravenous dose, a shortlived distribution phase (t1/2α) is sometimes seen. An a phase, however, is hardly discernible in over 250 profiles arising from oral doses administered during five single dose bioavailability studies. Almost all such profiles appear to follow single-compartment model predictions. With precautions to avoid a potential a phase, a terminal log-linear slope can be fitted by least squares analysis with a relative standard error in the slope determination almost always less than 6%. Covariance analysis confirms statistically that 39 of the 60 participating individuals varied in their β on the different occasions each was required to take a dose during the course of a crossover bioavailability trial. In one study, even though each individual was observed on only two occasions, 9 out of 12 showed statistically identifiable variation in β. Fluctuations in β of 60% can be seen. Changes of 30% or greater are common and can occur within 3 or 4 days. Thus real, large, and potentially frequent changes in β of theophylline have been identified in a majority of normal subjects. These changes do not appear to be confined to either sex, to smokers or nonsmokers, or to heavier or lighter individuals. No chronological pattern has, as yet, been recognized in the intraindividual variability in β.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01062330
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