Aim:Testosterone undecanoate (TU) is metabolized by nonspecific esterases in blood to testosterone (T). Typical clinical practice has been to analyze testosterone in human serum. The degradation of TU to testosterone was evaluated in conditions typically used in clinical studies.Methods & Results:Freshly collected whole blood was fortified with TU at known concentration. Serum was prepared and T concentration was determined by LC–MS/MS. It was observed that TU degrades extensively to T in human blood under conditions typical of harvesting serum causing overestimation of T concentration of up to 243%. These results were confirmed in a clinical study in which serum and plasma samples were compared.Conclusion:It was demonstrated that T must be analyzed in enzyme-inhibited plasma when TU is the administered medication.

No abstract

Clopidogrel, a thienopyridine derivative, is a potent antiplatelet drug that inhibits adenosine diphosphate (ADP)-mediated platelet activation and aggregation by selectively and irreversibly binding to platelet P2Y 12 purinergic receptor (1). Results of a large clinical trial have demonstrated an overall benefit of clopidogrel over aspirin in the prevention of vascular ischemic events (myocardial infarction, stroke, vascular death) in patients with a history of symptomatic atherosclerotic disease (2). However, platelet inhibition by clopidogrel is highly variable, and patients with reduced platelet inhibition have an increased risk of major cardiovascular events (3, 4). Two randomized, single dose, 2-period, 2-sequence crossover studies were conducted to evaluate the comparative bioavailability of two clopidogrel formulations under fasting and fed conditions. Assessment of bioequivalence was based upon measurement of plasma concentrations of the parent drug, clopidogrel, and its major (inactive) metabolite, clopidogrel carboxylic acid, using improved methanol-free extraction. Bioequivalence of Krka's formulation to the innovator's formulation was demonstrated under both fasting and fed conditions on 205 volunteers. Confidence intervals for AUC 0-t , AUC 0-inf and C max of clopidogrel and its main metabolite were well within the acceptance range of 80.00 to 125.00 %. Food substantially increased the bioavailability of clopidogrel from both formulations, while no effect of food on the extent and rate of exposure to the metabolite was observed. The effect of food was comparable between the two formulations, as indicated by the same direction and rank of food impact on the bioavailability of both formulations.

The high throughput is routinely used for the first steps of drug development such as drug discovery screening and toxicity. However, for PK analysis of regulated studies, the requirements and difficulties to achieve high-throughput analysis are more demanding due to regulatory guidelines that are not needed for early steps of drug discovery. High-throughput analysis can be required for any drug type from small molecules to larger ones. Contract research organizations must be prepared to deliver the results associated to these studies in a fast turnaround. Herein, we will describe the challenges encountered by a laboratory in order to go from low- to high-throughput analysis.

Incurred sample reanalysis (ISR) is now commonly practiced in regulated bioanalytical laboratories. With an average ISR success rate of 95% or higher and an increasing number of ISR tests being conducted, more and more situations deserve scientific evaluation or investigation for the unmatched reassay results revealed in ISR tests even though they meet the acceptance criteria. First, should an investigation be initiated when an ISR test is acceptable? How large a discrepancy or what situation would warrant an investigation? What would be the impact on a study? How would investigations regarding unmatched reassay results be conducted? What are the main root causes identified? Can normal random errors cause a large discrepancy in unfavorable combinations? How could the timeline and cost be affected? All these questions are addressed in this paper with five real case examples.