Abstract
Five absorption rate models have been compared for describing cefetamet data in 34 adults after oral administration of cefetamet pivoxil with food alone or in combination with either an antacid or an H2 antagonist. A sequential zero- then first-order input process provided the most flexible description of the absorption rate of cefetamet. If the first-order rate constant is linked to the zero- order input parameters the model can be interpreted as the consequence of solubility-limited absorption. While a sequential input is theoretically reasonable to assume, the first-order process appeared to be independent of the zero-order input. A population-based approach was applied to estimate the effect of dose and gastric pH increase on absorption and disposition. There appeared to be a dose-associated change in several parameters. The most marked change was an increase in volume of distribution of cefetamet. Treatments expected to increase gastric pH slowed the first-order component of the absorption process. Three models for estimating the extent of bioavailability have been compared using observations from 18 adults and 13 children receiving iv cefetamet and oral cefetamet pivoxil on two separate occasions. The most consistent estimates of the disposition parameters and the extent of bioavailability were achieved with the sequential zero- and first- order model under the assumption that steady slate volume of distribution and nonrenal clearance were the same after iv and oral treatment.
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Abbreviations
- ANOVA:
-
Analysis of variance
- ASC:
-
Ascending oral dose study
- CL :
-
Total body clearance
- CL NR :
-
Nonrenal clearance
- CL R :
-
Renal clearance
- C p :
-
Observed cefetamet plasma concentration
- CV :
-
Coefficient of variation
- Dose :
-
Dose of cefetamet
- F :
-
Unavailability
- FAD:
-
unavailability study in adults
- FCH:
-
Bioavailability study in children
- F K0 :
-
Fraction of the dose absorbed by a zero-order process
- fPH :
-
Factor describing the influence of antacid or H2-blocker comedication
- KA:
-
First-order absorption rate
- K0:
-
Zero-order absorption rate
- K0KA:
-
Sequential independent zero- and first-order absorption rate
- K0KA* :
-
Sequential linked zero- and first-order absorption rate
- k a :
-
Absorption rate constant when absorption is estimated by the sequential independent zero- and first-order absorption rate
- k *a :
-
Absorption rate constant when absorption is estimated by the sequential linked zero- and first-order absorption rate
- K m :
-
Michaelis-Menten constant
- LL :
-
Log Likelihood
- Λ1 :
-
Elimination rate constant for first exponential
- ΛZ :
-
Elimination rate constant for second exponential
- MM:
-
Saturable absorption rate
- pH:
-
−Log hydrogen ion concentration
- PH:
-
Interaction study with antacid and H2-blocker
- pwr :
-
Power function parameter
- SC :
-
Schwarz criterion
- SE :
-
Standard error
- SLOPEv SS :
-
Factor characterizing the influence on volume of distribution
- T :
-
Time after administration
- T 1/2 :
-
Half-life for terminal phase
- T K0 :
-
Period of time during which the absorption rate is zero-order (constant)
- T lag :
-
Lag time before absorption commences
- V 1 :
-
Volume of the central (first) compartment
- V max :
-
Maximum absorption rate
- Vss :
-
Volume of distribution at steady state
- Vss,pop :
-
Mean values forV ss in the population
- Vss,TV :
-
Typical value ofV ss predicted in the population
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Holford, N.H.G., Ambros, R.J. & Stoeckel, K. Models for describing absorption rate and estimating extent of bioavailability: Application to cefetamet pivoxil. Journal of Pharmacokinetics and Biopharmaceutics 20, 421–442 (1992). https://doi.org/10.1007/BF01061464
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DOI: https://doi.org/10.1007/BF01061464