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Bioavailability Section

Correcting endogenous concentrations of testosterone influences bioequivalence and shows the superiority of TDS®-testosterone versus Androgel®

Z. Chik, A. Johnston, A.T. Tucker, K. Kirby and C.A. Alam

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Volume 47 p. 262 - 268

Abstract

Z. Chik¹, A. Johnston², A.T. Tucker²,³, K. Kirby⁴ and C.A. Alam⁵

¹Department of Pharmacology, Faculty of Medicine, University of Malaya, Kuala Lumpur Malaysia, ²Clinical Pharmacology, ³The Ernest Cooke Clinical Microvascular Unit, St Bartholomew’s Hospital, Barts & The London NHS Trust, London, UK, ⁴Langford Institute, North Palm Beach, FL, USA, and, ⁵Bone and Joint Research Unit, William Harvey Research Institute, Barts and The London, Queen Mary’s School of Medicine and Dentistry, London, UK
Aim: Circulating concentrations of endogenous compounds such as testosterone, complicate the analysis of pharmacokinetic parameters when these compounds are administered exogenously. This study examines the influence of three correction methods of accounting for endogenous concentrations on the determination of bioequivalence between two testosterone formulations. Methods: 12 healthy males received 50 mg TDS^®-testosterone, TDS^®-placebo, and 50 mg Androgel^® in a randomized placebo controlled study. Three correction methods (1,2 and 3) to remove the influence of endogenous testosterone from the exogenous blood concentrations data were carried out before the calculation of the AUC and C_max. The relative bioavailabilities between two treatments were then performed for the AUC and C_max for all the corrected and uncorrected data. Correction 4 was performed on the AUC and the C_max values and the average values were calculated for both active treatments. Results: The relative bioavailability comparison of the AUC and C_max, showed that the TDS^®-testosterone and Androgel^® was bioequivalent by using uncorrected data (CI: 93 – 120%; AUC_0-12 and 88 – 117%; C_max). However, they were not bioequivalent when using all the corrections data ((Corr. 1; CI: 52 – 106%; AUC_0-12 and 50 – 258%; C_max), (Corr. 2; CI: 71 – 655%; AUC_0-12 and 87 – 286%; C_max), (Corr. 3; CI: 67 – 315%; AUC_0-12 and 88 – 157%; C_max)). TDS^®-testosterone also showed the higher AUC_0-12 and C_max compared to Androgel^® for uncorrected and all the Corrections 1, 2, 3 and 4. Conclusions: Different results obtained in the relative bioavailability between TDS^®-testosterone and Androgel^® for uncorrected data and corrected data, suggests that correcting endogenous concentrations is important for the proper determination of bioequivalent for endogenous compounds such as testosterone.Correspondence to:
Z. Chik, PhD; Department of Pharmacology, Faculty of Medicine, University of Malaya, 50603 Kuala Lumpur, Malysia
Email: [email protected]

Bioavailability Section

Comparative bioavailability study of two salbutamol tablets in healthy adult volunteers

Z. Chik, R.C. Basu, R. Pendek, T.C. Lee and Z. Mohamed

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42.00 $

Volume 47 p. 413 - 418

Abstract

Z. Chik¹, R.C. Basu¹, R. Pendek², T.C. Lee³ and Z. Mohamed¹

¹Department of Pharmacology, ²Department of Medicine, Faculty of Medicine, University of Malaya, Kuala Lumpur and ³Info Kinetic Sdn. Bhd., University Science Malaysia, Penang, Malaysia
This study was carried out to compare the rate and extent of absorption of a generic salbutamol in oral dosage form (Brethmol, 4mg) with the proprietary equivalent product (Ventolin^®, 4mg), in healthy adult subjects, under fasting conditions. The study was a single dose, randomized, two way crossover study with a four-week washout period. It involved 22 healthy volunteers who received a single dose (4mg) of the test and the reference products after an overnight fast of at least 10 hours. Blood samples were collected at pre-dose and a serial of 14 samples were collected from each of the subject from 1h until 48 h post-dose. Plasma concentrations of salbutamol were analyzed using GCMS method. The mean AUC_0-¥ values were 91.26 and 96.45 h.ng/ml for reference and test product, respectively. The mean C_max values were 12.26 and 12.38 ng/ml and the mean t_max values were 2.80 and 2.33 hours for reference and test product, respectively. Analysis of variance showed that the 90% confidence intervals on the relative difference of the ratio for the AUC_0-¥ and the C_max for the test and reference products were contained within the bioequivalence limit (80 – 125%) (C_max: 89.8 – 110.5% and AUC_0-¥: 91.6 – 121.5%). There was no statistically significant difference for the t_max between the test and reference formulations (p = 0.30). The test formulation was found to be bioequivalent to the reference formulation with regard to AUC_0-¥ and C_max. There was no statistically significant difference in Brethmol and Ventolin^® t_max. In conclusion, Brethmol and Ventolin^® are bioequivalent in healthy subjects.Correspondence to:
Z. Chik
Department of Pharmacology
Faculty of Medicine
University of Malaya
50603 Kuala Lumpur, Malaysia
Email: [email protected]

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