Variability in the bioavailability of phenytoin capsules in males and females.

PURPOSE: To determine inter-lot and intra-subject variability in the bioavailability of the 100 mg extended phenytoin sodium capsules. In addition, to determine the effect of gender and menstrual cycle on phenytoin bioavailability. METHODS: Three different lots of extended phenytoin sodium capsules were given to 12 healthy male and 12 healthy female subjects in a crossover fashion. One of the lots was also given a second time to each subject. Plasma phenytoin was determined, using an HPLC assay, in samples collected over a 73-hr period after each dose. RESULTS: The mean Cmax for the four administrations ranged from 1.71-1.79 microg/ml and mean AUC(0-infinity) values from ranged 53.0-54.1 microg*hr/ml. The elimination half-life was 3 hr shorter, and the AUC(0-infinity) adjusted for the mg/kg dose was 30% lower for females. Average bioequivalence was demonstrated between the three lots for both Cmax and AUC(0-infinity) based on the BE limit of 80-125%. Further, all confidence intervals of AUC(0-infinity) fell within the limit of 90-111%. There were no differences in the confidence limits for Cmax and AUC(0-infinity) determined separately for males and females. Also, there was no difference in the mean Cmax or AUC(0-infinity) for females when analyzed as a function of the week of their menstrual cycle. Individual bioequivalence was demonstrated between three lots of phenytoin using the constant-scaled method, but not the reference-scaled method. CONCLUSIONS: There was very little difference in the bioavailability of the three lots of phenytoin. Females exhibited a lower AUC(0-infinity) than males after adjustment of dose for body weight, but their inclusion in the study did not affect the assessment of bioequivalence. When dose was not adjusted for body weight, no difference in AUC(0-infinity) was seen between males and females.

The effect of gelatin cross-linking on the bioequivalence of hard and soft gelatin acetaminophen capsules.

PURPOSE: To determine if changes in the in vitro dissolution of hard and soft gelatin acetaminophen capsules, which result from gelatin crosslinking, are predictive of changes in the bioavailability of the capsules in humans. METHODS: Both hard and soft gelatin capsules were "stressed" by a controlled exposure to formaldehyde, resulting in unstressed, moderately stressed and highly stressed capsules. In vitro dissolution studies were conducted using water or SGF with and without pepsin as the media. Separate 24-subject, 3-way crossover human bioequivalence studies were performed on the unstressed and stressed acetaminophen capsules. Plasma acetaminophen was determined by high performance liquid chromatography (HPLC) for 12 hr after each dose. RESULTS: The in vitro rate of dissolution of hard and soft gelatin capsules was decreased by crosslinking. The bioequivalence studies showed that both hard and soft gelatin capsules, which failed to meet the USP dissolution specification in water, but complied when tested in SGF containing pepsin, were bioequivalent to the unstressed control capsules. The capsules that were cross-linked to the greatest extent were not bioequivalent to the unstressed control capsules, based on Cmax. A trend toward an increase in Cmax with increased level of cross-linking was observed, but this was only significant for the severely stressed capsules. CONCLUSIONS: On the basis of this study a two-tier in vitro dissolution test was developed using enzymes to distinguish between bioequivalent and bioinequivalent gelatin capsules.

The relative bioavailability and in vivo-in vitro correlations for four marketed carbamazepine tablets.

PURPOSE: To determine if three marketed generic carbamazepine tablets were bioequivalent to the innovator formulation, as well as to each other. In addition, to examine in vivo-in vitro relationships among the four formulations. METHODS: Each formulation was given as a single dose to 18 healthy male and female subjects using a crossover design. Blood samples were collected for 169 hr. Carbamazepine was assayed by HPLC with UV detection. RESULTS: In vivo fraction absorbed plots indicated that the three generic formulations were absorbed more rapidly than the innovator product, and the mean time of maximum plasma concentration was 6-7 hr sooner for the generic formulations. The mean maximum plasma concentration ranged from 17-19 percent higher for the generic products compared to the innovator, and the 90% confidence limits for Cmax data ranged from 11 1% to 126%. The mean AUC(0-infinity) for the generic products ranged from 101-104% compared to the innovator, and the confidence limits for AUC ranged from 97-108%. CONCLUSIONS: The generic products were all more rapidly absorbed than the innovator, but simulations of steady-state concentrations indicated that it would be unlikely that these differences would have any significant clinical effect. An excellent association was seen between the Cmax and the percent of drug dissolved in vitro. The correlation was used to accurately predict the Cmax of four other 200 mg tablets evaluated in an earlier study.

Lack of in vivo/in vitro correlations for 50 mg and 250 mg primidone tablets.

PURPOSE: To determine if large differences in the in vitro dissolution profiles for primidone tablets would result in significant bioavailability differences. METHODS: Two separate bioavailability studies were conducted. The first study used 18 healthy subjects and compared the bioavailability of an old 50 mg tablet formulation, a new 50 mg tablet formulation, and a suspension containing 50 mg/ml of primidone. The second study enrolled 24 subjects who were to receive a new 250 mg tablet formulation, two lots of an old 250 mg tablet formulation and a 250 mg tablet from a second manufacturer. In vitro dissolution was conducted over 90 minutes, using USP 23 Apparatus 2 at 50 rpm, with 900 ml of water. RESULTS: Dissolution at 90 minutes for the old and new 50 mg tablets was approximately 20% and 100%, respectively. The dissolution of the four 250 mg tablets ranged from approximately 30% to 100%. The 50 mg tablet that dissolved slower had a longer Tmax and a 14% lower Cmax than the more rapidly dissolving tablet, but the AUC(0-infinity) values differed by only 3%. Only nine subjects completed the 250 mg study because of side effects. The differences in Cmax and AUC(0-infinity) among the four 250 mg tablets were less than 7%. CONCLUSIONS: Even though there were large differences in the in vitro dissolution of the 50 mg and the 250 mg primidone tablets, the two 50 mg tablets were shown to be bioequivalent, as were the four 250 mg tablets.

Interfacing gradient elution ion-exchange chromatography and low-angle laser light-scattering photometry for analysis of proteins.

Molecular weights (MWs) of different proteins were determined by interfacing gradient elution ion-exchange chromatography and low-angle laser light-scattering photometry (IEC-LALLS). A high-performance strong cation-exchange column was used to elute proteins using fast (5 min) and conventional (15-30 min) gradients. The eluted proteins were characterized on-line by determining their MWs using LALLS. The specific refractive index (RI) increment (dn/dc) and the RI of the solvent used over the gradient range were determined off-line and used to calculate the absolute weight-average MWs. Four proteins, ribonuclease A, alpha-chymotrypsinogen A, trypsinogen and beta-lactoglobulin A (beta-LACT) were studied. Accurate MWs were obtained for all the proteins using fast and conventional gradients, except for beta-LACT, which aggregated as a function of the gradient employed. The degree of aggregation of beta-LACT increased as the rapidity of the gradient was increased over a fixed gradient range. This study indicated that it is possible to separate and characterize proteins rapidly using IEC-LALLS.

Pharmacologic disposition of chlorozotocin in mice.

Cholorozotocin is a water-soluble chloroethylnitrosourea with the cytotoxic group attached to the C2 position of glucose. The distribution of the alkylating and carbamoylating moieties of the chlorozotocin molecule was determined in mice following the ip administration of an LD10 dose: 20 mg/kg. The half-life (T 0.5) for the plasma disappearance of intact drug was 5 minutes. The plasma disappearance of the ethyl-14C group was biphasic up to 120 minutes after administration; the T 0.5 of the initial phase was 17.5 minutes and the T 0.5 of the prolonged second phase was107 minutes. The disappearance of glucose-14C chlorozotocin followed kinetics similar to the chloroethyl-labeled compound. Fifteen minutes after administration, ethyl-14C drug concentrated maximally in the liver (194 nmols/g of tissue) and the kidney (131 nmols/g of tissue). Uptake into the bone marrow at 60 minutes after ip administration of the ethyl-labeled drug was 6.6 pmols of the ethyl-14C group covalently bound to proteins and nucleic acids per 10(7) nucleated cells. The concentration of ethyl-14C drug in the brain remained at 4 mnols/g of tissue up to 2 hours after administration, reflecting the water-soluble property of this new nitrosourea.