2012 white paper on recent issues in bioanalysis and alignment of multiple guidelines.

Over 400 professionals representing pharmaceutical companies, CROs, and multiple regulatory agencies participated in the 6th Workshop on Recent Issues in Bioanalysis (WRIB). Like the previous sessions, this event was in the format of a practical, focused, highly interactive and informative workshop aiming for high-quality, improved regulatory compliance and scientific excellence. Numerous 'hot' topics in bioanalysis of both small and large molecules were shared and discussed, leading to consensus and recommendations among panelists and attendees representing the bioanalytical community. The major outcome of this year's workshop was the noticeable alignment of multiple bioanalytical guidance/guidelines from different regulatory agencies. This represents a concrete step forward in the global harmonization of bioanalytical activities. The present 2012 White Paper acts as a practical and useful reference document that provides key information and solutions on several topics and issues in the constantly evolving world of bioanalysis.

Perspectives on microsampling: DBS.

The concept of microsampling and particularly the dried blood spot methodology has been widely known to the scientific community for considerable time. Yet, there is no formal standard approach available to date for the pharmaceutical community to benefit from, in its regulatory interactions. This article discusses the various aspects of these issues and provides a framework within which a standard set of procedures can be adopted.

US FDA/EMA harmonization of their bioanalytical guidance/guideline and activities of the Global Bioanalytical Consortium.

The 2011 annual conference of the American Association of Pharmaceutical Scientists, held in Washington DC, USA, hosted a roundtable entitled: 'Update of the US FDA/European Medicines Agency (EMA) harmonization of their bioanalytical guidance - Global Bioanalytical Consortium activity and impact on small and large molecules.' The roundtable was initiated with a presentation from CT Viswanathan on the history of the revision of the FDA guideline on bioanalytical method validation. It was followed by a presentation by Jan Welink who presented an update on the final European Medicines Agency guideline on bioanalytical method validation with relevance to ongoing harmonization efforts. The final presentation was by Fabio Garofolo on the progress of the Global Bioanalytical Consortium harmonization teams for small and large molecules. Brian Booth and Sam Haidar of the FDA updated the audience on the status of the revision of the FDA bioanalytical guidance. The roundtable was moderated by Stephen Lowes.

2011 White paper on recent issues in bioanalysis and regulatory findings from audits and inspections.

The 5th Workshop on Recent Issues in Bioanalysis (WRIB) was organized by the Calibration and Validation Group as a 2-day full immersion workshop for pharmaceutical companies, CROs and regulatory agencies to discuss, review, share perspectives, provide potential solutions and agree upon a consistent approach to recent issues in the bioanalysis of both small and large molecules. High quality, better compliance to regulations and scientific excellence are the foundation of this workshop. As in the previous editions of this significant event, recommendations were made and a consensus was reached among panelists and attendees, including industry leaders and regulatory experts representing the global bioanalytical community, on many 'hot' topics in bioanalysis. This 2011 White Paper is based on the conclusions from this workshop, and aims to provide a practical reference guide on those topics.

Regulatory observations in bioanalytical determinations.

The concept of measuring analytes in biological media is a long-established area of the quantitative sciences that is employed in many sectors. While academic research and R&D units of private firms have been in the forefront of developing complex methodologies, it is the regulatory environment that has brought the focus and rigor to the quality control of the quantitative determination of drug concentration in biological samples. In this article, the author examines the regulatory findings discovered during the course of several years of auditing bioanalytical work. The outcomes of these findings underscore the importance of quality method validation to ensure the reliability of the data generated. The failure to ensure the reliability of these data can lead to potential risks in the health management of millions of people in the USA.

Workshop report and follow-up--AAPS Workshop on current topics in GLP bioanalysis: Assay reproducibility for incurred samples--implications of Crystal City recommendations.

The Conference Report of the 3rd AAPS/FDA Bioanalytical Workshop (Crystal City III) endorsed the concept that assay methods supporting bioanalytical data in submissions must demonstrate assay reproducibility by using incurred samples. The present Workshop was convened to provide a forum for discussion and consensus building about incurred sample assay reproducibility for both nonclinical and clinical studies. Information about current regulatory perspectives on incurred sample reanalysis (ISR) was presented, implications of ISR for both large and small molecules were discussed, and the steering committee put forth recommendations for performing ISR. These recommendations from the Workshop, along with the subsequent evolution of approaches leading to a robust ISR program, may be used by scientists performing bioanalytical assays for regulated studies to provide additional confirmation of assay reproducibility for incurred samples.

Quantitative bioanalytical methods validation and implementation: best practices for chromatographic and ligand binding assays.

The Third AAPS/FDA Bioanalytical Workshop, entitled "Quantitative Bioanalytical Methods Validation and Implementation: Best Practices for Chromatographic and Ligand Binding Assays" was held on May 1-3, 2006 in Arlington, VA. The format of this workshop consisted of presentations on bioanalytical topics, followed by discussion sessions where these topics could be debated, with the goal of reaching consensus, or identifying subjects where addition input or clarification was required. The discussion also addressed bioanalytical validation requirements of regulatory agencies, with the purpose of clarifying expectations for regulatory submissions. The proceedings from each day were reviewed and summarized in the evening sessions among the speakers and moderators of the day. The consensus summary was presented back to the workshop on the last day and was further debated. This communication represents the distillate of the workshop proceedings and provides the summary of consensus reached and also contains the validation topics where no consensus was reached.

Effects of humidity and temperature on in vitro dissolution of carbamazepine tablets.

The rate and extent of dissolution of various approved marketed carbamazepine (CBZ) tablets exposed to 33, 52, 75, and 97% relative humidities at both room temperature and 40 degrees C, and saturated water vapor at room temperature were compared to fresh unstressed tablets. The dissolution data indicate that exposure of CBZ tablets to high humidity and temperature can have a profound effect on tablet disintegration and dissolution. The dissolution rates of some batches of CBZ products exposed to 97% humidity at 40 degrees C or saturated water vapor at room temperature were drastically reduced in only 6-7 days.

High performance liquid chromatographic analysis of six conjugated and unconjugated estrogens in serum.

Six estrogens-estrone, equilin, estradiol, sodium estrone sulphate, sodium equilin sulphate and sodium 17-alpha-dihydroequilin sulphate in dog serum were successfully separated and quantified by a high performance liquid chromatographic method developed in our laboratories. The mobile phase was optimized by studying the effects of an organic modifier (acetonitrile) and an ion pairing reagent (tetrabutylammonium hydroxide). The serum sample work-up procedure was designed to recover both conjugated and unconjugated estrogens. The optimum method involved acetonitrile to precipitate serum proteins/peptides and extract estrogens. Residues were reconstituted in 50% acetonitrile in water for injection. The detection limits for these six estrogens via UV detection ranged from 0.5 to 5 ng on-column with a signal-to-noise ratio (S/N) of 10 for a 20 microL injection and via fluorescence 0.1 ng on-column for 17-beta-estradiol. Validation data are included for all six estrogens.

Pharmacokinetic evaluation of drug interactions with anti-HIV drugs, II: Effect of 2',3'-dideoxyinosine (ddI) on zidovudine kinetics in monkeys.

The pharmacokinetic basis of a drug interaction between zidovudine (AZT) and 2',3'-dideoxyinosine (ddI) was investigated in normal monkeys. Five animals received 20 mg/kg of AZT intragastrically in the absence and presence of ddI. ddI was administered intravenously to produce steady-state ddI plasma concentrations for 30 min. Plasma and urine samples were analyzed for AZT, its major glucuronide metabolite, GAZT, and ddI by high-performance liquid chromatography (HPLC). Resultant AZT and GAZT concentration data were analyzed by noncompartmental methods. Statistical analysis indicated no differences in AZT's apparent total clearance, apparent volume of distribution at steady-state, and elimination half-life due to ddI, however, the mean apparent total clearance decreased from 2.92 to 1.67 L/h/kg, and the mean apparent volume of distribution at steady-state decreased from 5.79 to 3.43 L/kg in the presence of ddI. Incomplete urine collections in most animals prevented conclusions from being made about ddI's effect on renal elimination parameters. Nonetheless, the urinary GAZT/AZT ratio, a parameter not influenced by incomplete urine collection, was significantly reduced in the presence of ddI. Although additional studies will be useful to characterize the full importance of the interaction, there is evidence to suggest that both renal and metabolic elimination of AZT and renal elimination of GAZT may be inhibited by ddI.

Pharmacokinetic evaluation of drug interactions with zidovudine. I: Probenecid and zidovudine in monkeys.

Pharmacokinetic evaluation of a drug interaction between zidovudine (AZT) and probenecid was conducted in monkeys. Six animals received 20 mg/kg of AZT as single intragastric (ig) and iv doses in the absence and presence of 50 mg/kg of probenecid administered ig. Plasma concentrations of AZT and its 5'-glucuronide metabolite (AZTG) were quantitated for 12 h by HPLC. Amounts of AZT and AZTG in urine were also measured, as were probenecid plasma concentrations. Non-compartmental methods were used to obtain pharmacokinetic parameters for AZT and AZTG. In the presence of probenecid, the total clearance of AZT decreased by 50%, renal clearance decreased, and elimination half-life increased. The volume of distribution at steady-state and systemic bioavailability of AZT were not significantly altered by probenecid. The areas under the plasma concentration-time curves and terminal half-lives of AZTG were increased, and renal clearances of AZTG were decreased. The alterations in AZT and AZTG pharmacokinetic parameters are consistent with inhibition of metabolism and renal tubular secretion by probenecid. Since AZT was administered by both oral and iv routes, clearance, volume of distribution, and bioavailability parameters were independently determined. Based on data reported for humans on the zidovudine-probenecid interaction, monkeys appear to be appropriate animal models for the evaluation of zidovudine drug interactions.

Analytical methods validation: bioavailability, bioequivalence and pharmacokinetic studies. Conference report.

This is a summary report of the conference on Analytical Methods Validation: Bioavailability, Bioequivalence and Pharmacokinetic Studies. The conference was held from December 3 to 5, 1990 in the Washington, DC area and was sponsored by the American Association of Pharmaceutical Scientists, US Food and Drug Administration, Federation International Pharmaceutique, Health Protection Branch (Canada) and Association of Official Analytical Chemists. The purpose of the report is to represent our assessment of the major agreements and issues discussed at the conference. The report is also intended to provide guiding principles for validation of analytical methods employed in bioavailability, bioequivalence and pharmacokinetic studies in man and animals. The objectives of the conference were: 1. To reach a consensus on what should be required in analytical methods validation and the procedures to establish validation; 2. To determine processes of application of the validation procedures in the bioavailability, bioequivalence and pharmacokinetic studies; 3. To develop a report on analytical methods validation (which may be referred to in developing future formal guidelines). Acceptable standards for documenting and validating analytical methods with regard to processes, parameters or data treatments were discussed because of their importance in assessment of pharmacokinetic, bioavailability and bioequivalence studies. Other topics which were considered essential in the conduct of pharmacokinetic studies or in establishing bioequivalency criteria, including measurement of drug metabolites and stereoselective determinations, were also deliberated.

Pharmacokinetics of rifampin in children. II. Oral bioavailability.

The absolute bioavailability of oral rifampin was determined in 20 pediatric patients. Intravenous doses of rifampin (mean 287 mg/m2) were compared with p.o. doses (mean 324 mg/m2). Serum concentrations of rifampin, 25-O-desacetylrifampicin, and 3-formylrifamycin SV were determined by high performance liquid chromatography. Following a 1/2-h intravenous infusion, serum rifampin concentrations declined in a monoexponential fashion. Pharmacokinetic analysis of the rifampin serum concentration data indicated that only 50 +/- 22% of a freshly prepared p.o. suspension was absorbed. The rifampin elimination half-life following i.v. administration (2.25 +/- 0.64 h) was not different from that observed following p.o. dose administration (2.61 +/- 1.35 h). Peak rifampin concentrations were significantly higher following i.v. administration when corrected to a 300 mg/m2 dose (27.4 vs. 9.1 micrograms/ml, respectively, p less than 0.0001) than after p.o. administration. The peak concentration following a p.o. dose occurred at 2.0 +/- 0.9 h. The ratio of desacetylrifampicin to rifampin areas under the curves were similar for i.v. and p.o. routes of administration (0.23 vs. 0.19), suggesting linear metabolism of rifampin to this metabolite. 3-formylrifamycin SV concentrations were lower than those of desacetylrifampicin and were detectable in less than half of the patients. The results of this study indicate the need for larger p.o. doses when serum concentrations similar to those obtained following intravenous doses are desired.

Diurnal oscillations of CSF valproate in monkey.

Valproate (VPA) was administered to four rhesus monkeys by constant-rate intravenous infusion for two weeks under controlled conditions. Plasma and CSF samples were collected for a period of 27 hours at 3-hour intervals during steady-state and post-infusion periods. The mean correlation coefficient between total plasma and CSF VPA concentrations was found to be 0.78 +/- 0.09. The CSF VPA levels reflected the changes in free VPA in plasma but the two were not equivalent. Diurnal fluctuations in CSF VPA concentration were similar to those found in plasma but the inter-animal variation was greater in CSF than in plasma.

Bioavailability of regular and controlled-release chlorpheniramine products.

The bioavailability of chlorpheniramine regular-release versus controlled-release products was compared using 15 human subjects. The dosage forms evaluated were an 8-mg barrier coated-bead capsule, an 8-mg repeat action tablet, two 4-mg tablets, and 4- and 8-mg syrups. Single doses of each product were administered orally in a 5-way crossover study, plasma samples were collected at specific time intervals, and chlorpheniramine levels assayed by HPLC. Pharmacokinetic analysis was based on a two-compartment open model. The average plasma elimination half-life of chlorpheniramine was calculated to be approximately 18.3 hr. The controlled-release products gave a higher Cmax than the 4-mg syrup, but less than two 4-mg tablets. The controlled-release products also extended the time necessary to attain peak drug levels compared to the 4- and 8-mg syrups. The area under the curve (AUC) data for the controlled-release products was not equivalent to equal amounts of the regular-release products. The study indicated that while the controlled-release chlorpheniramine products were successful in prolonging the time course of absorption, this was at the expense of incomplete bioavailability of the drug.

Diurnal oscillations in plasma protein binding of valproic acid.

In view of the observed variation of valproic acid (VPA) free fraction (fp) during a dosing interval and the competitive binding effect of free fatty acids (FFA) in vitro, this study was designed to address the existence of diurnal variations in the fp of VPA. Six subjects were hospitalized at 7 a.m. for 25 h, and plasma samples were collected every 2 h. The protocol was repeated in 4 of the 6 subjects one week later. In vitro binding of VPA (100 micrograms/ml) was determined by equilibrium dialysis (14C-VPA), and FFAs were assayed colorimetrically. Phenytoin (PHT) binding was also determined for comparison. VPA fp ranged from 8.10 +/- 1.16 to 9.63 +/- 1.54. Intrasubject variability was also measured by the ratio of maximum to minimum fp values (fp max/fp min) over 24 h: This ratio ranged from 1.30 to 1.68 (mean +/- %SD = 1.51 +/- 7.7%, n = 10). For PHT, fp ranged from 10.88 +/- 0.50 to 12.39 +/- 1.07, and fp max/fp min from 1.09 to 1.31 (1.17 +/- 5.1%, n = 10). The fp max was observed between 2 and 6 a.m. in 7 out of 10 cases for VPA and 5 out of 10 cases for PHT. FFA levels, although in the normal range, varied two- to fourfold within 24 h. A significant correlation was observed between mean FFA levels at each sampling time and the corresponding fp values for VPA (p less than 0.001), but not for PHT.

Plasma protein binding interaction between valproic and salicylic acids in rhesus monkeys.

The effects of three levels of salicylic acid on the steady-state plasma concentrations of free and total valproic acid were examined in catheterized rhesus monkeys. Valproate was infused intravenously for a total of 41 hr, and salicylate was added after the first 8 hr. The three salicylate infusions were randomly assigned to each monkey. Valproate free fraction was determined by equilibrium dialysis. Statistically significant increases in valproate free fraction and total body clearance were observed after addition of salicylic acid. The increase in valproate clearance was positively correlated with the molar ratio of salicylate to valproate steady-state plasma concentrations. There was no significant change in valproate free concentration after salicylate treatment. The proposed mechanism of this in vivo interaction includes plasma protein binding displacement with no change in valproate intrinsic clearance.