Displaying publications 41 - 60 of 99 in total

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  1. Yuen KH, Wong JW, Yap SP, Billa N
    Int J Clin Pharmacol Ther, 2001 Jan;39(1):37-40.
    PMID: 11204936
    OBJECTIVE: The aim of the present communication is to provide information regarding the intrasubject coefficent of variation obtained from 30 bioequivalence studies covering 16 drugs which can be used for estimation of sample size. Additionally, an attempt was also made to estimate the test power of each of the studies conducted.

    METHODS: The intrasubject coefficient of variation was estimated from the residual mean square error obtained from analysis of variance of the parameters AUC0-infinity, Cmax and Cmax/AUC0-infinity after logarithmic transformation. The test power in the analyses of the above parameters was subsequently estimated using nomograms provided by Diletti et al. [1991].

    RESULTS AND CONCLUSION: Thirty products covering 16 drugs were studied in which 22 were immediate-release (including one dispersible tablet) and 8 were sustained-release formulations. The intrasubject coefficient of variation for the parameter AUC0-infinity was smaller than Cmax, and hence considerably more studies were able to attain a power of greater than 80% using 12 volunteers for the AUC0-infinity, compared to the Cmax. However, the variability in the Cmax could be reduced by using the parameter Cmax/ AUC0-infinity, and thus, provide a more realistic estimation of sample size, since the latter reflects only the rate of absorption and not both the rate and extent as in the case of Cmax [Endrenyi et al. 1991].

  2. Yuen KH, Wong JW, Billa N, Choy WP, Julianto T
    Med J Malaysia, 1999 Dec;54(4):482-6.
    PMID: 11072466
    The bioavailability of a generic preparation of ketoconazole (Zorinax from Xepa-Soul Pattinson, Malaysia) was evaluated in comparison with the innovator product (Nizoral from Janssen Pharmaceutica, Switzerland). Eighteen healthy male volunteers participated in the study conducted according to a two-way crossover design. The bioavailability was compared using the parameters, total area under the plasma concentration-time curve (AUC0-infinity), peak plasma concentration (Cmax) and time to reach peak plasma concentration (Tmax). No statistically significant difference was observed between the values of the two products in all the three parameters. Moreover, the 90% confidence interval for the ratio of the logarithmic transformed AUC0-infinity and Cmax values of Zorinax over Nizoral was found to lie between 0.82-1.04 and 0.83-1.02, respectively, being within the acceptable equivalence limit of 0.80-1.25. These findings indicate that the two preparations are comparable in the extent and rate of absorption. In addition, the elimination rate constant (ke) and apparent volume of distribution (Vd) were calculated. For both parameters, there was no statistically significant difference between the values obtained from the data of the two preparations. Moreover, the values are comparable to those reported in the literature.
  3. Yuen KH, Wong JW, Billa N, Julianto T, Toh WT
    Int J Clin Pharmacol Ther, 1999 Jul;37(7):319-22.
    PMID: 10442505
    The bioavailability of a generic preparation of metformin (Diabetmin from Hovid Sdn Bhd) was evaluated in comparison with a proprietary product (Glucophage from Lipha Pharma Ltd., UK).
  4. Yap SP, Julianto T, Wong JW, Yuen KH
    J Chromatogr B Biomed Sci Appl, 1999 Dec 10;735(2):279-83.
    PMID: 10670741
    A simple high-performance liquid chromatographic method using fluorescence detection was developed for the determination of vitamin E especially delta-, gamma- and alpha-tocotrienols in human plasma. The method entailed direct injection of plasma sample after deproteinization using a 3:2 mixture of acetonitrile-tetrahydrofuran. The mobile phase comprised 0.5% (v/v) of distilled water in methanol. Analyses were run at a flow-rate of 1.5 ml/min with the detector operating at an excitation wavelength of 296 nm and emission wavelength of 330 nm. This method is specific and sensitive, with a quantification limit of approximately 40, 34 and 16 ng/ml for alpha-, gamma- and delta-tocotrienol, respectively. The mean absolute recovery values were about 98% while the within-day and between-day relative standard deviation and percent error values of the assay method were all less than 12.0% for alpha-, gamma- and delta-tocotrienol. The calibration curve was linear over a concentration range of 40-2500, 30-4000 and 16-1000 ng/ml for alpha-, gamma- and delta-tocotrienol, respectively. Application of the method in a bioavailability study for determination of the above compounds was also demonstrated.
  5. Lim R, Liong ML, Lau YK, Yuen KH
    Neurourol Urodyn, 2017 02;36(2):438-442.
    PMID: 26693962 DOI: 10.1002/nau.22950
    AIMS: To enable the use of the International Consultation on Incontinence Questionnaire-Urinary Incontinence Short Form (ICIQ-UI SF) and ICIQ-Lower Urinary Tract Symptoms Quality of Life (ICIQ-LUTSqol) in Southeast Asia, we translated and subsequently evaluated their validity (content and discriminant validity), reliability (internal consistency and test-retest reliability), and responsiveness in female patients with stress urinary incontinence.

    METHODS: Permission was obtained to translate the English versions into Malay and subsequently validate them, and to validate the existing Chinese versions. The translated questionnaires were taken for pilot testing. Validation was carried out for the face/content and discriminant validity. Reliability was assessed for test-retest and internal consistency using Cronbach's alpha and intraclass correlation coefficient respectively. The responsiveness was calculated via effect size and standardized response mean.

    RESULTS: Ten patients were recruited for the pilot testing. The English and Chinese versions had "substantial" or "almost perfect" agreement as measured by weighted Kappa. 284 participants (139 patients with stress urinary incontinence and 145 healthy volunteers) were included in the subsequent phases. The ICIQ-UI SF and ICIQ-LUTSqol had good discriminant validity. The ICIQ-UI SF had moderate internal consistency although the ICIQ-LUTSqol had good internal consistency. Both questionnaires had high test-retest reliability. Responsiveness was established with a moderate to large effect size and a standardized response mean.

    CONCLUSIONS: The English, Chinese, and Malay versions each proved to be valid and reliable in our Malaysian population, thereby enabling more cross-cultural research in this region. Neurourol. Neurourol. Urodynam. 36:438-442, 2017. © 2015 Wiley Periodicals, Inc.

  6. Ong SG, Ming LC, Lee KS, Yuen KH
    Pharmaceutics, 2016;8(3).
    PMID: 27571096 DOI: 10.3390/pharmaceutics8030025
    The objective of the present study was to investigate the influence of the encapsulation efficiency and size of liposome on the oral bioavailability of griseofulvin-loaded liposomes. Griseofulvin-loaded liposomes with desired characteristics were prepared from pro-liposome using various techniques. To study the effect of encapsulation efficiency, three preparations of griseofulvin, namely, griseofulvin aqueous suspension and two griseofulvin-loaded liposomes with different amounts of griseofulvin encapsulated [i.e., F1 (32%) and F2(98%)], were administered to rats. On the other hand, to study the effect of liposome size, the rats were given three different griseofulvin-loaded liposomes of various sizes, generated via different mechanical dispersion techniques [i.e., FTS (142 nm), MS (357 nm) and NS (813 nm)], but with essentially similar encapsulation efficiencies (about 93%). Results indicated that the extent of bioavailability of griseofulvin was improved 1.7-2.0 times when given in the form of liposomes (F1) compared to griseofulvin suspension. Besides that, there was an approximately two-fold enhancement of the extent of bioavailability following administration of griseofulvin-loaded liposomes with higher encapsulation efficiency (F2), compared to those of F1. Also, the results showed that the extent of bioavailability of liposomal formulations with smaller sizes were higher by approximately three times compared to liposomal formulation of a larger size. Nevertheless, a further size reduction of griseofulvin-loaded liposome (≤400 nm) did not promote the uptake or bioavailability of griseofulvin. In conclusion, high drug encapsulation efficiency and small liposome size could enhance the oral bioavailability of griseofulvin-loaded liposomes and therefore these two parameters deserve careful consideration during formulation.
  7. Lee EH, Lim SS, Yuen KH, Lee CY
    J Pharm Pharmacol, 2019 May;71(5):860-868.
    PMID: 30515807 DOI: 10.1111/jphp.13052
    OBJECTIVES: This study aims to investigate the blood-brain barrier (BBB) permeability of curcumin analogues with shortened linkers and their ability to protect against amyloid-beta toxicity in a whole organism model.

    METHOD: Four curcumin analogues were synthesized. These analogues and curcumin were evaluated for their BBB permeability in the parallel artificial membrane permeability assay. The transgenic Caenorhabditis elegansGMC101 that expresses human Aβ1-42 was treated with the compounds to evaluate their ability to delay Aβ-induced paralysis. Expression of skn-1mRNA was examined on nematodes treated with selected efficacious compounds. In vitro Aβ aggregation in the presence of the compounds was performed.

    KEY FINDINGS: The four analogues showed improved BBB permeability vs curcumin in the PAMPA with the hemi-analogue C4 having the highest permeability coefficient. At 100 μm, analogues C1 and C4 as well as curcumin significantly prolonged the survival of the nematodes protecting against Aβ toxicity. However, only curcumin and C4 showed protection at lower concentrations. skn-1mRNA was significantly elevated in nematodes treated with curcumin and C4 indicating SKN-1/Nrf activation as a possible mode of action.

    CONCLUSIONS: Analogue C4 provides a new lead for the development of a curcumin-based compound for protection against Aβ toxicity with an improved BBB permeability.

  8. Ling SS, Yuen KH, Magosso E, Barker SA
    J Pharm Pharmacol, 2009 Apr;61(4):445-9.
    PMID: 19298690 DOI: 10.1211/jpp/61.04.0005
    A liposome preparation that is amenable to receptor-mediated endocytosis has been developed to enhance the oral bioavailability of poorly absorbable peptidomimetic drugs by use of folic acid as the mediator of liposomal uptake.
  9. Rasool AH, Rahman AR, Yuen KH, Wong AR
    Arch Pharm Res, 2008 Sep;31(9):1212-7.
    PMID: 18806966 DOI: 10.1007/s12272-001-1291-5
    The tocotrienol vitamin E has potent antioxidant property, however absorption is low due to high lipid solubility. A self emulsifying preparation of tocotrienol rich vitamin E (SF-TRE) had been reported to increase their bioavailability. This randomized, placebo controlled, blinded end point clinical study aimed to determine the effects of 50, 100 and 200 mg daily of SF-TRE and placebo for two months on arterial compliance and vitamin E blood levels. Assessment of arterial compliance by carotid femoral pulse wave velocity (PWV) and augmentation index (AI), plasma vitamin E, serum total cholesterol and low density lipoprotein cholesterol were taken before and after 2 months' treatment in 36 healthy males. Un-supplemented tocotrienol levels were low, after treatment, all SF-TRE treated groups had significantly higher plasma alpha, delta and delta tocotrienol concentrations compared to placebo. Augmentation index change from baseline to end of treatment for groups placebo, 50, 100, and 200 mg were 2.22+/-1.54, -6.59+/-2.84, -8.72+/-3.77, and -6.27+/-2.67% respectively (p=0.049, 0.049, and 0.047 respectively). Groups 100 and 200 mg showed significant improvement after treatment with pulse wave velocity reductions of 0.77 m/s and 0.65 m/s respectively (p=0.007 and p=0.002). There was no effect of SF-TRE on serum lipids. We conclude that there was a trend towards improvement in arterial compliance with 2 months' of SF-TRE.
  10. Yuen KH, Peh KK, Billa N, Chan KL, Toh WT
    Drug Dev Ind Pharm, 1998 Feb;24(2):193-6.
    PMID: 15605452
    The bioavailability of a generic preparation of acyclovir (Avorax) was compared with the innovator product, Zovirax. Twelve healthy volunteers participated in the study, conducted according to a randomized, two-way crossover design. The preparations were compared using the parameters area under the plasma concentration time curve (AUC(0-infinity), peak plasma concentration (Cmax), and time to reach peak plasma concentration (Tmax). No statistically significant difference was observed between the Tmax or the logarithmic transformed AUC(0-infinity) and C(max) values of the two preparations. In addition, the 90% confidence interval for the ratio of the logarithmic transformed AUC(0-infinity) values of Avorax over those of Zovirax was found to lie between 0.85 and 1.06, while that of the logarithmic transformed Cmax values was between 0.95 and 1.25, being within the bioequivalence limit of 0.80-1.25. Moreover, the elimination rate constant (k(e)), elimination half-life (t(1/2)), and apparent volume of distribution (Vd) values obtained with the two preparations were comparable and not significantly different statistically.
  11. Yuen KH, Wong JW, Peh KK, Julianto T, Choy WP
    Drug Dev Ind Pharm, 2000 Jul;26(7):803-7.
    PMID: 10872103
    The bioavailability of a generic preparation of pentoxifylline sustained-release (SR) tablet was evaluated in comparison with a proprietary product (Trental 400). For the study, 12 healthy male volunteers participated; the study was conducted according to a randomized, two-way crossover design. The bioavailability was compared using the parameters total area under the plasma level-time curve AUC0-infinity, peak plasma concentration Cmax, and time to reach peak plasma concentration Tmax. No statistically significant difference was observed between the values of the two products in all three parameters. The 90% confidence interval for the ratio of the logarithmic transformed AUC0-infinity values of the generic pentoxifylline over those of Trental 400 was found to lie between 0.83 and 1.00, while that of the parameter Cmax was between 0.91 and 1.29. In addition, elimination half-life t1/2 and apparent volume of distribution Vd were calculated. There was no statistically significant difference between the t1/2 Vd values obtained from the data of the two preparations.
  12. Peh KK, Yuen KH, Wong JW, Toh WT
    Drug Dev Ind Pharm, 1999 Mar;25(3):357-60.
    PMID: 10071830
    A study was conducted to compare the bioavailability of a generic product of atenolol (Normaten FC) with the innovator product, Tenormin. Twelve healthy adult volunteers participated in the study conducted according to a randomized, two-way crossover design. The preparations were compared using area under the plasma concentration-time curve AUC0-infinity, peak plasma concentration Cmax, and time to reach peak plasma concentration Tmax. No statistically significant difference was obtained between the Tmax values and the logarithmic transformed AUC0-infinity and Cmax values of the two products. Moreover, the 90% confidence interval for the ratio of the logarithmically transformed AUC0-infinity values of Normaten FC over those of Tenormin was found to lie between 0.82 and 0.98, while that of the logarithmically transformed Cmax values was between 0.82 and 1.09, both being within the bioequivalence limit of 0.80-1.25. The values of elimination half-life t1/2 between the two products were also found comparable and not significantly different statistically. The t1/2 values obtained in our study were slightly longer than those reported in the literature for other population groups.
  13. Yuen KH, Peh KK, Chan KL, Toh WT
    Drug Dev Ind Pharm, 1998 Oct;24(10):955-9.
    PMID: 9876550
    A study was conducted to compare the in vivo bioavailability of a generic metoprolol tablet preparation (Metoprolol) with that of the innovator product, Betaloc. Both preparations have a labeled dose of 100 mg metoprolol tartrate. Twelve healthy adult male volunteers participated in the study, which was conducted according to a standard two-way crossover design with a washout period of 1 week. The bioavailability was compared using the total area under the plasma level versus time curve (AUC0-infinity), peak plasma concentration (Cmax), and time to reach peak plasma concentration (Tmax). No statistically significant difference was observed between the logarithmically transformed AUC0-infinity values or the logarithmically transformed Cmax values of the two preparations. However, a statistically significant difference was observed between the Tmax values, but may not be therapeutically significant or important. Moreover, the 90% confidence interval (CI) for the ratio of the logarithmically transformed AUC0-infinity values of Metoprolol over those of Betaloc was calculated to be between 0.94 and 1.02, while that of Cmax was between 0.98 and 1.01, both of which are within the acceptable limit of 0.80-1.25. From the data obtained, it was also observed that a high proportion of our volunteers of Asian origin appeared to be poor metabolizers of metoprolol, which was consistent with what had been observed in our previous study of another preparation of metoprolol.
  14. Chan KL, Yuen KH, Jinadasa S, Peh KK, Toh WT
    Planta Med, 1997 Feb;63(1):66-9.
    PMID: 9063097
    A high-performance liquid chromatography assay equipped with a glassy carbon electrode for electrochemical detection (HPLC-ECD) was developed at reductive mode for the analysis of artemisinin, the antimalarial drug from Artemisia annua (Asteraceae) in human plasma. This method was selective, sensitive, and produced satisfactory recovery, precision, and accuracy. Analysis of plasma samples from 8 male volunteers given 10 mg kg-1 of artemisinin orally as an aqueous suspension showed a mean peak plasma concentration (Cmax) of 580.89 ng ml-1 +/- 88.64 SD at 2.5 h +/- 0.5 SD after dosing, and the mean area under the plasma concentration-time curve (AUC0-infinity) was 2227.57 ng h ml-1 +/- 677.22 SD. In addition, the elimination rate constant (Ke), elimination half-life (t1/2), and apparent volume of distribution (Vd) were calculated to be 0.2971 h-1 +/- 0.0644 SD, 2.42 h +/- 0.46 SD, and 16.26 l kg-1 +/- 3.44 SD, respectively.
  15. Lim R, Liong ML, Lau YK, Yuen KH
    Eur J Obstet Gynecol Reprod Biol, 2018 Mar;222:109-112.
    PMID: 29408740 DOI: 10.1016/j.ejogrb.2018.01.024
    OBJECTIVE: In order for a measure to reliably evaluate treatment efficacy, it is important that the measure used has adequate responsiveness. However, the responsiveness of the Golombok Rust Inventory of Sexual Satisfaction (GRISS) questionnaire, a highly recommended questionnaire by the International Consultation of Incontinence to assess sexual function in patients with incontinence, has not been established. To enable the use of GRISS to measure change in sexual function following incontinence treatment, we evaluated the short- and long-term responsiveness of the GRISS in couples with female stress urinary incontinence partners.
    STUDY DESIGN: Forty-eight couples with female stress urinary incontinence partners were included in the study. The GRISS, a 28-item multidimensional measure, comprises two sets of questionnaires to assess sexual function in both male and female partners. Responsiveness was investigated using data from our recent randomized controlled trials evaluating efficacy of pulsed magnetic stimulation for treatment of female patients with stress urinary incontinence. Effect size index and standardized response mean were used to measure responsiveness of the English and Chinese versions of GRISS.
    RESULTS: For short-term responsiveness, the overall female and male GRISS scores had effect sizes and standardized response means ranging from 0.60 to 0.83 and 0.44 to 0.78 respectively. For long-term responsiveness, the overall female and male GRISS scores had effect sizes and standardized response means ranging from 0.59 to 0.77 and 0.48 to 0.79 respectively.
    CONCLUSION: In conclusion, the English and Chinese versions of GRISS had adequate responsiveness for use in couples with incontinent partners. The GRISS can be a useful measure to detect change in sexual function of couples following treatment of females with stress urinary incontinence.
    Study site: urology or gynecology clinics, hospitals, Pulau Pinang; general population
  16. Lim R, Liong ML, Leong WS, Yuen KH
    BJU Int, 2018 05;121(5):805-810.
    PMID: 29319927 DOI: 10.1111/bju.14121
    OBJECTIVE: To review measures used in recent randomised controlled trials (RCTs) evaluating stress urinary incontinence (SUI) treatments and to propose the most relevant outcome measure that should be included in future trials.

    MATERIALS AND METHODS: We identified RCTs for SUI interventions published between January 2015 and July 2017. We listed the objective and subjective outcome measures used in eligible trials in the literature search. Using data from our RCT conducted from 2013 to 2016 evaluating pulsed magnetic stimulation for SUI, we analysed the correlation between all measures.

    RESULTS: A total of 45 RCTs were included; 28 (62%) involved surgical interventions. The most frequently used objective and subjective measures were the cough stress test and International Consultation on Incontinence Questionnaire-Urinary Incontinence Short Form (ICIQ-UI SF), respectively. In all, 24 different validated questionnaires were administered in the 42 studies that used subjective outcome measure. Analyses of measures used in our trial showed that all measures were significantly correlated with each other except for pelvic floor muscle function. The ICIQ-UI SF showed the highest correlation coefficients (0.587-0.733) with all outcome measures.

    CONCLUSION: The outcome measures used in recent trials were inconsistent. The ICIQ-UI SF had the highest correlation with all measures in our trial; however, further studies evaluating correlation of measures in other patient cohorts are needed to corroborate our present results. We propose the use of ICIQ-UI SF, as the most relevant outcome measure, in future trials evaluating efficacy of SUI interventions.

  17. Loon YH, Wong JW, Yap SP, Yuen KH
    PMID: 15664346
    A simple liquid chromatographic method was developed for the simultaneous determination of flavonoids from Orthosiphon stamineus Benth, namely sinensitin, eupatorin and 3'-hydroxy-5,6,7,4'-tetramethoxyflavone, in plasma. Prior to analysis, the flavonoids and the internal standard (naproxen) were extracted from plasma samples using a 1:1 mixture of ethyl acetate and chloroform. The detection and quantification limits for the three flavonoids were similar being 3 and 5 ng/ml, respectively. The within-day and between-day accuracy values, expressed as percentage of true values, for the three flavonoids were between 95 and 107%, while the corresponding precision, expressed as coefficients of variation, for the three flavonoids were less than 14%. In addition, the mean recovery values of the extraction procedure for all the flavonoids were between 92 and 114%. The calibration curves were linear over a concentration range of 5-4000 ng/ml. The present method was applied to analyse plasma samples obtained from a pilot study using rats in which the mean absolute oral bioavailability values for sinensitin, eupatorin and 3'-hydroxy-5,6,7,4'-tetramethoxyflavone was 9.4, 1.0 and 1.5%, respectively.
  18. Ling SS, Yuen KH, Barker SA
    PMID: 12450550
    A high-performance liquid chromatographic method with ultraviolet (UV) detection was developed for measuring cefotaxime in rat and human plasma. The method used direct injection of the plasma supernatant after deproteinization with 70% perchloric acid. Degradation of cefotaxime in acidic medium was retarded by adding phosphate buffer before centrifuging the sample. The mobile phase was 0.05 M aqueous ammonium acetate-acetonitrile-tetrahydrofuran (87:11:2, v/v) adjusted to pH 5.5. Analysis was run at a flow-rate of 1.0 ml/min, and a detection wavelength of 254 nm was used. The method has a quantification limit of 0.20 microgram/ml. The within- and between-day coefficients of variation and accuracy values were less than 8% and +/-3%, respectively, while the recovery values were greater than 87% over the concentration range tested (0.20-50 microgram/ml). The speed, sensitivity, specificity and reproducibility of this method make it particularly suitable for the routine determination of cefotaxime in human plasma. Moreover, only a relatively small sample plasma volume (100 microliter) is required, allowing this method to be applied to samples taken from neonates.
  19. Chiong HS, Yong YK, Ahmad Z, Sulaiman MR, Zakaria ZA, Yuen KH, et al.
    Int J Nanomedicine, 2013;8:1245-55.
    PMID: 23569374 DOI: 10.2147/IJN.S42801
    Liposomal drug delivery systems, a promising lipid-based nanoparticle technology, have been known to play significant roles in improving the safety and efficacy of an encapsulated drug.
  20. Salman SA, Amrah S, Wahab MS, Ismail Z, Ismail R, Yuen KH, et al.
    J Clin Pharm Ther, 2010 Dec;35(6):691-6.
    PMID: 21054461 DOI: 10.1111/j.1365-2710.2009.01147.x
    Eurycoma longifolia (E. longifolia), a herb commonly consumed for its aphrodisiac properties, is widely used by Asian males. This may include hypertensive patients receiving propranolol which may cause sexual dysfunction as one of its side-effects. There is no published study of the potential pharmacokinetic interaction between propranolol and the herb.
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