The use of imaging in the early development of neuropharmacological drugs: a survey of approved NDAs.

The aim of the study was to evaluate the use of imaging in the development of neuropharmacological drugs. All New Drug Applications (NDAs) approved from 1995 through 2004 in the Division of Neuropharmacological Drug Products at the Food and Drug Administration were surveyed for imaging studies. Imaging literature was also reviewed with respect to antipsychotics and antidepressants. One hundred and six NDAs (35 new molecular entities (NMEs)) were approved; 15 of these NDAs (10 NMEs) had imaging studies. The primary imaging modality was positron emission tomography. Imaging was primarily conducted for drugs used in schizophrenia, depression, multiple sclerosis, and migraine. The majority evaluated receptor occupancy or proof of concept. Examples (including literature) are discussed as pertinent to dosage, efficacy, safety, or further development of a drug or class of drugs. Imaging contributes to optimal clinical development of central nervous system (CNS)-active drugs. Opportunities are available for its broader use, contributing to improved understanding of the clinical pharmacology of CNS-active drugs.

The antioxidant system beta-D(+) glucose-glucose oxidase-catalase: tests for pyrogenicity and antigenicity.

PURPOSE: beta-D(+) glucose-glucose oxidase (E.C.# 1.1.3.4)-catalase (E.C.# 1.11.1.6) (GO-CAT) is being investigated as a new antioxidant system for use in pharmaceutical solutions. This study reports the results of tests for pyrogenicity and antigenicity of GO-CAT derived from Aspergillus niger when used parenterally in autoclaved preparations. METHODS: The Limulus amebocyte lysate (LAL) method was used to test the pyrogenicity of native GO-CAT. Pyrogenicity/antigenicity was evaluated in vivo by injecting autoclaved GO-CAT into New Zealand white rabbits. Antigenicity was also evaluated by Ouchterlony and Western blotting. RESULTS: None of the native GO-CAT concentrations tested (up to 30.83 u/ml) produced a positive gel clot in the LAL test, thereby suggesting its non-pyrogenicity. The rabbits, which received seven injections of autoclaved GO-CAT over a period of eleven weeks, remained healthy during and after the GO-CAT injections. All Ouchterlony and Western blot assays using sera from rabbits injected with autoclaved GO-CAT were negative. Furthermore, autoclaved GO-CAT could not be detected in Ouchterlony assays using a mouse monoclonal antibody (GO40 mAb) to native A. niger glucose oxidase. Control samples containing native GO-CAT produced an antigen-antibody complex reaction in Ouchterlony assays against the GO40 mAb. Antigen-antibody complexes could be detected by non-denaturing PAGE in samples containing native GO-CAT/GO40 and boiled GO-CAT/GO40, but not in samples containing autoclaved GO-CAT/GO40. These results indicate autoclaved GO-CAT is neither pyrogenic nor antigenic. CONCLUSIONS: Based on these results, there is potential for the use of beta-D(+) glucose-glucose oxidase-catalase as an antioxidant system in pharmaceutical solutions, particularly in terminally autoclaved aqueous formulations for parenteral use.

In vivo drug-drug interaction studies--a survey of all new molecular entities approved from 1987 to 1997.

Ninety-eight new molecular entities applications approved between 1987 to 1991 (period I) and 193 applications for new molecular entities between 1992 to 1997 (period II) were surveyed for drug-drug interaction studies. In period I (used as a comparator), 32 applications contained drug-drug interaction studies for a total of 117 studies. In period II, 106 applications reported drug-drug interaction studies, and the number of studies per new molecular entity ranged from 0 to 15. Most studies (77%) were performed in healthy subjects, with 44% using crossover designs, 7% using parallel designs, and the remaining using fixed sequence designs. The most common dosing scheme for new molecular entities/interacting drug was multiple dose (47%), whereas single dose/multiple dose was used in 31% of studies, and single dose/single dose was used in 18% of studies. Of the 540 drug-drug interaction studies submitted in period II, 80 (15%) resulted in clinically significant labeling statements. Submissions for new molecular entities to the Center for Drug Evaluation and Research divisions most likely to include drug-drug interaction studies were neuropharmacology, cardiorenal, antiviral, and antiinfective drugs. Some drug classes such as oncology drug products and radioimaging products were least likely to include drug-drug interaction studies in their submissions. We conclude that the use of drug-drug interaction studies in the drug development process has increased between the two periods.

Evaluation of "external" predictability of an in vitro-in vivo correlation for an extended-release formulation containing metoprolol tartrate.

The purpose of this study was to examine the external predictability of an in vitro-in vivo correlation (IVIVC) for a metoprolol hydrophilic matrix extended-release formulation, with an acceptable internal predictability, in the presence of a range of formulation/manufacturing changes. In addition, this report evaluated the predictability of the IVIVC for another formulation of metoprolol tartrate differing in its release mechanism. Study 1 examined the scale up of a matrix extended-release tablet from a 3-kg small batch (I) to a 50-kg large batch (II). The second study examined the influence of scale and processing changes [3-kg small batch with fluid bed granulation and drying (III); 80-kg large batch with high shear granulation and microwave drying (IV), and a formulation with an alternate release mechanism formulated as a multiparticulate capsule (V)]. In vitro dissolution of all formulations (I-V) was conducted with a USP apparatus I at pH 6.8 and 150 rpm. Subjects received the metoprolol formulations, and serial blood samples were collected over 48 h and analyzed by a validated HPLC assay using fluorescence detection. A previously developed IVIVC was used to predict plasma profiles. Prediction errors (PE) were <10% for C(max) and area under the curve (AUC) of concentration versus time for I, II, and IV. The C(max) for III was slightly underestimated (11.7%); however, the PE of the AUC was <10%. Formulation V displayed a PE for C(max) > 20% and an AUC within 5% of observed values. The low PEs for C(max) and AUC observed for I-IV strongly suggest that the metoprolol IVIVC is externally valid, predictive of alternate processing methods (IV), scale-up (II, III), and allows the in vitro dissolution data to be used as a surrogate for validation studies. However, the lack of predictability for V supports the contention that IVIVCs are formulation specific.

In vitro metabolic interaction studies: experience of the Food and Drug Administration.

A total of 194 new molecular entities approved by the Food and Drug Administration between 1992 and 1997 were surveyed to determine the role of in vitro metabolic interactions in the conduct of drug-drug interaction studies and to examine the methods used in these studies. Approximately 30% of the submissions were found to have in vitro metabolism-based interaction studies, most of which were inhibitory in nature. Chemical inhibition was the most commonly used approach in studying drug interactions in vitro. In this article, an attempt to assess the quality of the chemical inhibition approach was made. Four areas were found to be often overlooked: (1) incubation time and concentrations of the drug, (2) the difference between inhibition constant (k(i)) and 50% inhibitory concentration (IC50) values, (3) the substrate-dependent inhibition potential, and (4) the metabolic genotype or phenotype of the liver donor. We discuss the pitfalls in estimating drug interactions when these four areas are overlooked.

Development and internal validation of an in vitro-in vivo correlation for a hydrophilic metoprolol tartrate extended release tablet formulation.

PURPOSE: To develop and validate internally an in vitro-in vivo correlation (IVIVC) for a hydrophilic matrix extended release metoprolol tablet. METHODS: In vitro dissolution of the metoprolol tablets was examined using the following methods: Apparatus II, pH 1.2 & 6.8 at 50 rpm and Apparatus I, pH 6.8, at 100 and 150 rpm. Seven healthy subjects received three metoprolol formulations (100 mg): slow, moderate, fast releasing and an oral solution (50 mg). Serial blood samples were collected over 48 hours and analyzed by a validated HPLC assay using fluorescence detection. The f2 metric (similarity factor) was used to analyze the dissolution data. Correlation models were developed using pooled fraction dissolved (FRD) and fraction absorbed (FRA) data from various combinations of the formulations. Predicted metoprolol concentrations were obtained by convolution of the in vivo dissolution rates. Prediction errors were estimated for Cmax and AUC to determine the validity of the correlation. RESULTS: Apparatus I operated at 150 rpm, and pH of 6.8 was found to be the most discriminating dissolution method. There was a significant linear relationship between FRD and FRA when using either two or three of the formulations. An average percent prediction error for Cmax and AUC for all formulations of less than 10% was found for all IVIVC models. CONCLUSIONS: The relatively low prediction errors for Cmax and AUC observed strongly suggest that the metoprolol IVIVC models are valid. The average percent prediction error of less than 10% indicates that the correlation is predictive and allows the associated dissolution data to be used as a surrogate for bioavailability studies.

beta-D(+) glucose-glucose oxidase-catalase for use as an antioxidant system.

The purpose of this study was to investigate the use of beta-D(+) glucose-glucose oxidase (EC 1.1.3.4)-catalase (EC 1.11.1.6) (BDG-GO-CAT) as a new antioxidant system in solutions. A novel method for estimation of activity of the system was developed using a dissolved oxygen (DO) meter and an oxygen probe. The method can be used to determine the enzymatic activity of the system at GO concentrations of 0.005 to 0.030 unit/ml, with an r2 of 0.995 for the linearity of the standard curve, and can be adapted for analysis in any solution. At room temperature of 23.0 degrees +/- 2.0 degrees C, the maximum activity of the BDG-GO-CAT system was found to occur at pH 5.40. The half-life values for the stability of GO-CAT in 0.10 M phosphate buffer solutions of pH 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, and 10.0 were 9.78, 49.43, 53.46, 36.51, 12.68, 1.84, and 0.80 weeks, respectively. Dextrose was used in place of beta-D(+) glucose for cost-saving purposes, and a standard curve for the activity of GO-CAT was obtained using 20 mg/ml dextrose. The BDG-GO-CAT was effective as a DO-scavenger in closed containers, when the containers were opened and exposed to atmosphere for 2 days between tests, and upon reclosing them. Pharmaceutical excipients such as ethanol, glycerin, propylene glycol, methylparaben, propylparaben, artificial strawberry flavor, and sodium benzoate did not show any adverse effect on the activity of BDG-GO-CAT. Sorbitol, high-fructose corn syrup, sucrose, and polyethylene glycol 3350 increased the rate of DO removal. Sodium carboxymethyl-cellulose (CMC) at 2.0% w/v decreased the rate of DO removal. These studies indicate that the BDG(dextrose)-GO-CAT system warrants serious consideration for use an antioxidant system in aqueous formulations.