Displaying publications 1 - 20 of 32 in total

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  1. Tan YT, Peh KK, Al-Hanba O
    J Pharm Pharm Sci, 2001 Jan-Apr;4(1):7-14.
    PMID: 11302785
    To investigate the interpolymer complexation between Carbopol 934P (CP) and various grades of polyvinylpyrrolidone (PVP) (K90, K32, C15, and VA/S-630).
  2. Tan YT, Peh KK, Al-Hanbali O
    AAPS PharmSciTech, 2000;1(3):E24.
    PMID: 14727910
    This study examined the mechanical (hardness, compressibility, adhesiveness, and cohesiveness) and rheological (zero-rate viscosity and thixotropy) properties of polyethylene glycol (PEG) gels that contain different ratios of Carbopol 934P (CP) and polyvinylpyrrolidone K90 (PVP). Mechanical properties were examined using a texture analyzer (TA-XT2), and rheological properties were examined using a rheometer (Rheomat 115A). In addition, lidocaine release from gels was evaluated using a release apparatus simulating the buccal condition. The results indicated that an increase in CP concentration significantly increased gel compressibility, hardness, and adhesiveness, factors that affect ease of gel removal from container, ease of gel application onto mucosal membrane, and gel bioadhesion. However, CP concentration was negatively correlated with gel cohesiveness, a factor representing structural reformation. In contrast, PVP concentration was negatively correlated with gel hardness and compressibility, but positively correlated with gel cohesiveness. All PEG gels exhibited pseudoplastic flow with thixotropy, indicating a general loss of consistency with increased shearing stress. Drug release T50% was affected by the flow rate of the simulated saliva solution. A reduction in the flow rate caused a slower drug release and hence a higher T50% value. In addition, drug release was significantly reduced as the concentrations of CP and PVP increased because of the increase in zero-rate viscosity of the gels. Response surfaces and contour plots of the dependent variables further substantiated that various combinations of CP and PVP in the PEG gels offered a wide range of mechanical, rheological, and drug-release characteristics. A combination of CP and PVP with complementary physical properties resulted in a prolonged buccal drug delivery.
  3. Tan YT, Ngoh GC, Chua ASM
    Bioresour Technol, 2019 Jun;281:359-366.
    PMID: 30831515 DOI: 10.1016/j.biortech.2019.02.010
    In this study, acidic deep eutectic solvents (DES) synthesized from various organic carboxylic acid hydrogen bond donors were applied to lignocellulosic oil palm empty fruit bunch (EFB) pretreatment. The influence of functional group types on acid and their molar ratios with hydrogen bond acceptor on lignin extraction were evaluated. The result showed presence of hydroxyl group and short alkyl chain enhanced biomass fractionation and lignin extraction. Choline chloride:lactic acid (CC-LA) with the ratio of 1:15 and choline chloride:formic acid (CC-FA) with 1:2 ratio extracted more than 60 wt% of lignin. CC-LA DES-extracted lignin (DEEL) exhibited comparable reactivity with technical and commercial lignin based on its phenolic hydroxyl content (3.33-3.72 mmol/glignin). Also, the DES-pretreated EFB comprised of enriched glucan content after biopolymer fractionation. Both DES-pretreated EFB and DEEL can be potential feedstock for subsequent conversion processes. This study presented DES as an effective and facile pretreatment method for reactive lignin extraction.
  4. Liew KB, Peh KK, Fung Tan YT
    Pak J Pharm Sci, 2014 Sep;27(5):1303-7.
    PMID: 25176366
    The effect of deprotenizing agents on recovery of donepezil hydrochloride in the development of a simple, rapid, selective and sensitive high performance liquid chromatography method for quantification of donepezil hydrochloride in human plasma was described. The deprotenizing agents were comprised of, perchloric acid, methanol, acetonitrile, chloroform and their mixtures. The chromatographic separation was carried out using reversed phase C18 column (Agilent Eclipse Plus C18) with UV detection at 268 nm. The mobile phase was comprised of 0.01 M potassium dihydrogen phosphate buffer, methanol and acetronitrile (50:30:20, v/v) adjusted to pH 2.7 with phosphoric acid (80%). A combination of perchloric acid and methanol gave a cleaner sample with a good recovery of donepezil hydrochloride of above 96%. The method showed intraday precision and accuracy in the range of 6.82% to 1.5% and 3.13% to 1.12% respectively, while interday precision and accuracy ranged between 1.06% to 4.71% and 13.01% to 6.43% respectively. The standard calibration curve was linear from 30ng/mL to 4000ng/mL, with a correlation coefficient of 0.9965±0.0034. The retention time of donepezil was 5.9 min with a run time of 7.0 min. The method can be applied to analyze large batch plasma samples in pharmacokinetic studies.
  5. Liew KB, Peh KK, Fung Tan YT
    Pak J Pharm Sci, 2013 Sep;26(5):961-6.
    PMID: 24035953
    An easy, fast and validated RV-HPLC method was invented to quantify donepezil hydrochloride in drug solution and orally disintegrating tablet. The separation was carried out using reversed phase C-18 column (Agilent Eclipse Plus C-18) with UV detection at 268 nm. Method optimization was tested using various composition of organic solvent. The mobile phase comprised of phosphate buffer (0.01M), methanol and acetonitrile (50:30:20, v/v) adjusted to pH 2.7 with phosphoric acid (80%) was found as the optimum mobile phase. The method showed intraday precision and accuracy in the range of 0.24% to -1.83% and -1.83% to 1.99% respectively, while interday precision and accuracy ranged between 1.41% to 1.81% and 0.11% to 1.90% respectively. The standard calibration curve was linear from 0.125 μg/mL to 16 μg/mL, with correlation coefficient of 0.9997±0.00016. The drug solution was stable under room temperature at least for 6 hours. System suitability studies were done. The average plate count was > 2000, tailing factor <1, and capacity factor of 3.30. The retention time was 5.6 min. The HPLC method was used to assay donepezil hydrochloride in tablet and dissolution study of in-house manufactured donepezil orally disintegrating tablet and original Aricept.
  6. Tan YT, Azanan MS, Hng SY, Eg KP, Jalaludin MY, Thong MK, et al.
    J Clin Sleep Med, 2024 Apr 03.
    PMID: 38557309 DOI: 10.5664/jcsm.11140
    STUDY OBJECTIVES: The effect of recombinant human growth hormone (rhGH) on sleep-disordered breathing (SDB) in Malaysian children with Prader-Willi syndrome (PWS) is under-investigated. We determined (a) the short- and long-term effects of rhGH and (b) factors associated with worsening SDB, in children with PWS on rhGH.

    METHODS: This retrospective study included children with PWS (with and without rhGH) who had at least one polysomnography (PSG). Outcomes measured were the presence of SDB: before and after starting rhGH and the progress of SDB with and without rhGH. Serial insulin-like growth factor-1 (IGF-1) measurements were recorded.

    RESULTS: One-hundred and thirteen PSGs were analyzed. The majority (92.3%) of initial PSGs had SDB with AHI median (IQR) 5.0 (2.6,16.3) events/h. The age for receiving rhGH was median (IQR) 1.9 (0.7, 3.4) years old. A third (36.8%) had worsening SDB after initiating rhGH, which was associated with higher IGF-1 levels post-rhGH (p=0.007). After a median of 5 years of rhGH, 73.6% maintained or reduced their positive airway pressure (PAP) settings. Without rhGH, 80% had increased their PAP settings. Worsening SDB while on rhGH was associated with higher BMI, lower rhGH dose, higher IGF-1 levels and non-15q deletion.

    CONCLUSIONS: Majority of Malaysian children with PWS had SDB. At initiation rhGH, one-third of patients had worsening SDB, associated with increased IGF-1 levels. Stabilization of SDB was more frequently seen in those on long-term rhGH. Worsening SDB while on rhGH was associated with a higher BMI, on a lower dose of rhGH, higher IGF-1 levels and non-15q deletion.

  7. Cheah JS, Yeo PP, Lui KF, Tan BY, Tan YT, Ng YK
    Med J Malaysia, 1982 Jun;37(2):141-9.
    PMID: 7132833
    A country-wide diabetic survey of the population (age 15 years and above) of Singapore shows that the prevalence of diabetes mellitus in Singapore is 1.99 percent. It is commoner in males (2.36 percent) than in females (1.64 percent). The prevalence of diabetes in the age group 15-39 years is only 0.40 percent and in the age group 40 years and older it is 5.08 percent. The prevalence of diabetes in Indians (6.07 percent) is significantly higher than that in Malays (2.43 percent) and Chinese (1.55 percent). Indian diabetics have an insignifi"cantly higher incidence of positive family of diabetes (12.7 percent) than Malays (10.9 percent) and Chinese (6.5 percent). Obesity was commoner in Malay diabetics (67.4 percent) than in Chinese diabetics (41.6 percent) and Indian diabetics (35.7 percent). The survey shows that 40.4 percent of the diabetics are known while 59.6 percent of the diabetics are newly diagnosed. The majority of the diabetics are treated with oral hypoglycaemic drugs (71.5 percent) and only 4.8 percent are receiving insulin injections. A mong the female diabetics, 63.0 percent have 4 or more pregnancies and large babies at birth are recorded in 12.3 percent. In the newly diagnosed diabetics, 64.3 percent have no symptoms. The complications of the diabetics are hypertension (26.8 percent), nephropathy (9.8 percent), retinopathy (8.5 percent), coronary heart disease (6.1 percent), skin infection (4.6 percent) and neuropathy (3.3 percent). The high prevalence of diabetes among the Indians is likely to be due to a genetic predisposition coupled with an environmental factor (obesity), although this hypothesis is not conclusively demonstrated by the present study.
  8. Tan YT, Chua ASM, Ngoh GC
    Bioresour Technol, 2020 Feb;297:122522.
    PMID: 31818720 DOI: 10.1016/j.biortech.2019.122522
    Since the introduction of deep eutectic solvent (DES) in biomass processing field, the efficiency of DES in lignocellulosic biopolymer model compounds' (cellulose, hemicellulose and lignin) solubilisation and conversion was widely recognized. Nevertheless, DES's potential for biorefinery application can be reflected more accurately through their performance in raw lignocellulosic biomass processing rather than model compound conversion. Therefore, this review examines the studies on raw lignocellulosic biomass fractionation using DES and the subsequent conversion of DES-fractionated products into bio-based products. The review stresses on three key parts: performance of varying types of DESs and pretreatment schemes for biopolymer fractionation, properties and conversion of fractionated saccharides as well as DES-extracted lignin. The prospects and challenges of DES implementation in biomass processing will also be discussed. This review provides a front-to-end view on the DES's performance, starting from pretreatment to DES-fractionated products conversion, which would be helpful in devising a comprehensive biomass utilization process.
  9. Liew KB, Loh GO, Tan YT, Peh KK
    Biomed Chromatogr, 2015 Jun;29(6):953-60.
    PMID: 25400284 DOI: 10.1002/bmc.3378
    A simple, rapid, specific and reliable UFLC coupled with ESI-MSMS assay method to simultaneously quantify sildenafil and N-desmethyl sildenafil, with loperamide as internal standard, was developed. Chromatographic separation was performed on a Thermo Scientific Accucore C18 column with an isocratic mobile phase composed of 0.1% v/v formic acid in purified water-methanol (20:80, v/v), at a flow rate of 0.3 mL/min. Sildenafil, N-desmethyl sildenafil and loperamide were detected with proton adducts at m/z 475.4 > 58.2, 461.3 > 85.2 and 477.0 > 266.1 in multiple reaction monitoring positive mode, respectively. Both analytes and internal standard were extracted by diethyl ether. The method was validated over a linear concentration range of 10-800 ng/mL for sildenafil and 10-600 ng/mL for N-desmethyl sildenafil with correlation coefficient (r(2) ) ≥0.9976 for sildenafil and (r(2) ) ≥0.9992 for N-desmethyl sildenafil. The method was precise, accurate and stable. The proposed method was applied to study the bioequivalence between a 100 mg dose of two pharmaceutical products: Viagra (original) and Edyfil (generic) products. AUC0-t , Cmax and Tmax were 2285.79 ng h/mL, 726.10 ng/mL and 0.94 h for Viagra and 2363.25 ng h/mL, 713.91 ng/mL and 0.83 hour for Edyfil. The 90% confidence interval of these parameters of this study fall within the regulatory range of 80-125%, hence they are considered as bioequivalent.
  10. Liew KB, Loh GO, Tan YT, Peh KK
    Biomed Chromatogr, 2014 Sep;28(9):1246-53.
    PMID: 24585432 DOI: 10.1002/bmc.3153
    The objectives of this study were to develop a new deproteinization method to extract amoxicillin from human plasma and evaluate the inter-ethnic variation of amoxicillin pharmacokinetics in healthy Malay volunteers. A single-dose, randomized, fasting, two-period, two-treatment, two-sequence crossover, open-label bioequivalence study was conducted in 18 healthy Malay adult male volunteers, with one week washout period. The drug concentration in the sample was analyzed using high-performance liquid chromatography (UV-vis HPLC). The mean (standard deviation) pharmacokinetic parameter results of Moxilen® were: peak concentration (Cmax ), 6.72 (1.56) µg/mL; area under the concentration-time graph (AUC0-8 ), 17.79 (4.29) µg/mL h; AUC0-∞ , 18.84 (4.62) µg/mL h. Those of YSP Amoxicillin® capsule were: Cmax , 6.69 (1.44) µg/mL; AUC0-8 , 18.69 (3.78) µg/mL h; AUC00-∞ , 19.95 (3.81) µg/mL h. The 90% confidence intervals for the logarithmic transformed Cmax , AUC0-8 and AUC0-∞ of Moxilen® vs YSP Amoxicillin® capsule was between 0.80 and 1.25. Both Cmax and AUC met the predetermined criteria for assuming bioequivalence. Both formulations were well tolerated. The results showed significant inter-ethnicity variation in pharmacokinetics of amoxicillin. The Cmax and AUC of amoxicillin in Malay population were slightly lower compared with other populations.
  11. Liew KB, Loh GO, Tan YT, Peh KK
    Biomed Chromatogr, 2014 Dec;28(12):1782-8.
    PMID: 24788875 DOI: 10.1002/bmc.3221
    A simple, rapid, specific and reliable high-performance liquid chromatographic assay of meloxicam in human plasma has been developed using a C18 reversed-phase analytical column. Reversed-phase chromatography was conducted using a mobile phase of 0.02 potassium dihydrogen phosphate (adjusted to pH 2.7 with phosphoric acid)-acetonitrile-triethylamine (35:65:0.05, v/v) with UV detection at 354 nm. The drug in human plasma was deproteinized using a combination of methanol and chloroform. This method is simple, rapid and consistent with a high recovery of meloxicam in human plasma ranging from 93.29 to 111.09%. Regression analysis for the calibration plot for plasma standards obtained for the drug concentrations between (25-4000) ng/mL indicated excellent linearity (r ≥ 0.9997). The proposed method was applied to study the bioequivalence between Mobic (original) and Melocam (generic) products. The study was conducted on using two tablets (4 × 7.5 mg) of each of the commercial product and the reference standard in a two-way open randomized crossover design involving 20 volunteers. Area under the concentration-time curve, peak concentration (C(max)) and time to reach C(max) were 72,868.61 ng h/mL, 2133.93 ng/mL and 4.06 h for Mobic, and 78,352.52 ng h/mL, 2525.18 ng/mL and 3.61 h for Melocam. Two C(max) were discovered in the pharmacokinetic profiles which confirm enterohepatic recirculation.
  12. Loh GO, Tan YT, Peh KK
    Carbohydr Polym, 2014 Jan 30;101:505-10.
    PMID: 24299805 DOI: 10.1016/j.carbpol.2013.09.084
    The effect of hydroxypropyl methylcellulose (HPMC) concentration on β-cyclodextrin (β-CD) solubilization of norfloxacin was examined. The solubility and dissolution of norfloxacin/β-CD and norfloxacin/β-CD/HPMC inclusion complexes were studied. The presence of β-CD increased significantly the solubility and dissolution of norfloxacin. The addition of HPMC until 5% (w/w) improved the solubilization of norfloxacin but further addition above 5% (w/w), decreased norfloxacin solubilization. Fourier transformed Infra-red (FTIR) showed that norfloxacin was successfully included into β-CD. Differential scanning calorimetry (DSC) showed that the norfloxacin endothermic peak shifted to a lower temperature with reduced intensity indicating the formation of inclusion complex. The addition of HPMC reduced further the intensity of norfloxacin endothermic peak. Most of the sharp and intense peaks of norfloxacin disappeared with the addition of HPMC. In conclusion, the concentration of hydrophilic polymer used to enhance β-CD solubilization of poorly soluble drugs is very critical.
  13. Aziz HA, Tan YT, Peh KK
    AAPS PharmSciTech, 2012 Mar;13(1):35-45.
    PMID: 22101965 DOI: 10.1208/s12249-011-9707-x
    Microencapsulation of water-soluble drugs using coacervation-phase separation method is very challenging, as these drugs partitioned into the aqueous polymeric solution, resulting in poor drug entrapment. For evaluating the effect of ovalbumin on the microencapsulation of drugs with different solubility, pseudoephedrine HCl, verapamil HCl, propranolol HCl, paracetamol, and curcuminoid were used. In addition, drug mixtures comprising of paracetamol and pseudoephedrine HCl were also studied. The morphology, encapsulation efficiency, particle size, and in vitro release profile were investigated. The results showed that the solubility of the drug determined the ratio of ovalbumin to be used for successful microencapsulation. The optimum ratios of drug, ovalbumin, and gelatin for water-soluble (pseudoephedrine HCl, verapamil HCl, and propranolol HCl), sparingly water-soluble (paracetamol), and water-insoluble (curcuminoid) drugs were found to be 1:1:2, 2:3:5, and 1:3:4. As for the drug mixture, the optimum ratio of drug, ovalbumin, and gelatin was 2:3:5. Encapsulated particles prepared at the optimum ratios showed high yield, drug loading, entrapment efficiency, and sustained release profiles. The solubility of drug affected the particle size of the encapsulated particle. Highly soluble drugs resulted in smaller particle size. In conclusion, addition of ovalbumin circumvented the partitioning effect, leading to the successful microencapsulation of water-soluble drugs.
  14. Liew KB, Tan YT, Peh KK
    AAPS PharmSciTech, 2012 Mar;13(1):134-42.
    PMID: 22167416 DOI: 10.1208/s12249-011-9729-4
    The aim of this study was to develop a taste-masked oral disintegrating film (ODF) containing donepezil, with fast disintegration time and suitable mechanical strength, for the treatment of Alzheimer's disease. Hydroxypropyl methylcellulose, corn starch, polyethylene glycol, lactose monohydrate and crosspovidone served as the hydrophilic polymeric bases of the ODF. The uniformity, in vitro disintegration time, drug release and the folding endurance of the ODF were examined. The in vitro results showed that 80% of donepezil hydrochloride was released within 5 minutes with mean disintegration time of 44 seconds. The result of the film flexibility test showed that the number of folding time to crack the film was 40 times, an indication of sufficient mechanical property for patient use. A single-dose, fasting, four-period, eight-treatment, double-blind study involving 16 healthy adult volunteers was performed to evaluate the in situ disintegration time and palatability of ODF. Five parameters, namely taste, aftertaste, mouthfeel, ease of handling and acceptance were evaluated. The mean in situ disintegration time of ODF was 49 seconds. ODF containing 7 mg of sucralose were more superior than saccharin and aspartame in terms of taste, aftertaste, mouthfeel and acceptance. Furthermore, the ODF was stable for at least 6 months when stored at 40°C and 75% relative humidity.
  15. Kit Loh GO, Ling Wong EY, Fung Tan YT, Lee YL, Chew CK, Mohd Sali ND, et al.
    Bioanalysis, 2021 Nov 08.
    PMID: 34743613 DOI: 10.4155/bio-2021-0185
    Aim: To develop an LC-MS/MS method for simultaneous determination of duloxetine and its metabolite, 4-hydroxy duloxetine glucuronide (4HDG) in human plasma and to investigate the potential back-conversion of 4HDG to duloxetine using stability study. Materials & methods: The LC-MS/MS method was validated according to the EMA and USFDA Bioanalytical Method Validation Guidelines and applied to pilot bioequivalence study. Results & conclusion: The method validation results were within the acceptance limits. The stability study and incurred sample reanalysis results ruled out the occurrence of back-conversion. The study highlighted the conduct of back-conversion test and the advantages of LC-MS/MS method in terms of sensitivity, specificity and low consumption of organic solvents.
  16. Liew KB, Tan YT, Peh KK
    Drug Dev Ind Pharm, 2015 Apr;41(4):583-93.
    PMID: 24495273 DOI: 10.3109/03639045.2014.884130
    Manufacturing process and superdisintegrants used in orally disintegrating tablet (ODT) formulation are often time discussed. However, the effect of suitable filler for ODT formulation is not explored thoroughly.
  17. Liew KB, Tan YT, Peh KK
    Drug Dev Ind Pharm, 2014 Jan;40(1):110-9.
    PMID: 23311593 DOI: 10.3109/03639045.2012.749889
    Difficulty in swallowing tablets or capsules has been identified as one of the contributing factors to non-compliance of geriatric patients. Although orally disintegrating tablet was designed for fast disintegration in mouth, the fear of taking solid tablets and the risk of choking for certain patient populations still exist.
  18. Cheah JS, Yeo PP, Thai AC, Lui KF, Wang KW, Tan YT, et al.
    Ann Acad Med Singap, 1985 Apr;14(2):232-9.
    PMID: 4037681
    Singapore is a tropical island city-state with a population of 2.4178 million consisting of Chinese (76.7%), Malays (14.7%), Indians (6.4%) and other races (2.2%). A diabetic survey of the adult population, aged 15 years and above, carried out in 1975, shows that the prevalence of diabetes is 1.99%; it is higher in males (2.36%) than in females (1.64%). It occurs mainly in the age group 40 years and above (5.08%) and is uncommon in the age group 15-39 years (0.40%). In males, the highest prevalence of diabetes (7.0%) is in the age group 45-49 years while in females the highest prevalence (7.2%) is in the age group 55-59 years. 43.3% of the diabetics are of normal weight while 44.3% are overweight and 12.4% are underweight. 59.6% of the diabetics are newly diagnosed while 40.4% are known diabetics; 64.3% of the newly diagnosed diabetics have no symptoms. The prevalence of diabetes among the Indians (6.07%) is significantly higher than that in Malays (2.43%) and Chinese (1.55%). Indian diabetics have a slightly higher positive family history of diabetes (12.7%) than Malays (10.9%) and Chinese (6.5%). Obesity is commoner in Malay diabetics (64.7%) than in Chinese (41.6%) and Indians (35.7%). The possible factors leading to the significantly higher prevalence of diabetes among the Indians compared to the other ethnic groups in Singapore are discussed. It is suggested that the Indian gene is susceptible to diabetes (diabetic genotype) and increased food consumption, altered lifestyle and greater obesity leads to the expression of diabetes.(ABSTRACT TRUNCATED AT 250 WORDS)
  19. Lee WW, Ooi BC, Thai AC, Loke KY, Tan YT, Rajan U, et al.
    Singapore Med J, 1998 Aug;39(8):359-62.
    PMID: 9844497
    To determine the incidence of insulin dependent diabetes mellitus (IDDM) in children 0-12 years of age in Singapore, which has a population of 2.9 million.
  20. Sahib MN, Abdulameer SA, Darwis Y, Peh KK, Tan YT
    Drug Des Devel Ther, 2012;6:29-42.
    PMID: 22393583
    The local treatment of lung disorders such as asthma and chronic obstructive pulmonary disease via pulmonary drug delivery offers many advantages over oral or intravenous routes of administration. This is because direct deposition of a drug at the diseased site increases local drug concentrations, which improves the pulmonary receptor occupancy and reduces the overall dose required, therefore reducing the side effects that result from high drug doses. From a clinical point of view, although jet nebulizers have been used for aerosol delivery of water-soluble compounds and micronized suspensions, their use with hydrophobic drugs has been inadequate.
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