Displaying publications 1 - 20 of 37 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. 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.
  5. Yuen KH, Peh KK, Billa N
    Drug Dev Ind Pharm, 1999 Mar;25(3):353-6.
    PMID: 10071829
    The bioavailability of a generic preparation of naltrexone (Narpan) was compared with the innovator product, Trexan. Twelve healthy volunteers participated in the study, conducted according to a completely randomized, two-way crossover design. The preparations were compared using the parameters 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 logarithmic transformed AUC0-infinity and the logarithmically transformed Cmax values of the two preparations. Also, no statistically significant difference was observed between the untransformed Tmax values. In addition, the 90% confidence interval for the ratio of the logarithmic transformed AUC0-infinity values of Narpan over those of Trexan was found to lie between 0.87 and 1.01, while that of the logarithmic transformed Cmax values was between 0.94 and 1.23, both being within the bioequivalence limit of 0.80-1.25. The numerical values of the elimination half-life (t1/2) obtained with the two preparations were also not significantly different and were comparable to those reported in the literature.
  6. Wen MM, El-Salamouni NS, El-Refaie WM, Hazzah HA, Ali MM, Tosi G, et al.
    J Control Release, 2017 01 10;245:95-107.
    PMID: 27889394 DOI: 10.1016/j.jconrel.2016.11.025
    Alzheimer's disease (AD) is a neurodegenerative disease with high prevalence in the rapidly growing elderly population in the developing world. The currently FDA approved drugs for the management of symptomatology of AD are marketed mainly as conventional oral medications. Due to their gastrointestinal side effects and lack of brain targeting, these drugs and dosage regiments hinder patient compliance and lead to treatment discontinuation. Nanotechnology-based drug delivery systems (NTDDS) administered by different routes can be considered as promising tools to improve patient compliance and achieve better therapeutic outcomes. Despite extensive research, literature screening revealed that clinical activities involving NTDDS application in research for AD are lagging compared to NTDDS for other diseases such as cancers. The industrial perspectives, processability, and cost/benefit ratio of using NTDDS for AD treatment are usually overlooked. Moreover, active and passive immunization against AD are by far the mostly studied alternative AD therapies because conventional oral drug therapy is not yielding satisfactorily results. NTDDS of approved drugs appear promising to transform this research from 'paper to clinic' and raise hope for AD sufferers and their caretakers. This review summarizes the recent studies conducted on NTDDS for AD treatment, with a primary focus on the industrial perspectives and processability. Additionally, it highlights the ongoing clinical trials for AD management.
  7. Tan SW, Billa N
    AAPS PharmSciTech, 2014 Apr;15(2):287-95.
    PMID: 24318197 DOI: 10.1208/s12249-013-0056-9
    We aimed to investigate the effects that natural lipids, theobroma oil (TO) and beeswax (BW), might have on the physical properties of formulated nanoparticles and also the degree of expulsion of encapsulated amphotericin B (AmB) from the nanoparticles during storage. Lecithin and sodium cholate were used as emulsifiers whilst oleic acid (OA) was used to study the influence of the state of orderliness/disorderliness within the matrices of the nanoparticles on the degree of AmB expulsion during storage. BW was found to effect larger z-average diameter compared with TO. Lecithin was found to augment the stability of the nanoparticles imparted by BW and TO during storage. An encapsulation efficiency (%EE) of 59% was recorded when TO was the sole lipid as against 42% from BW. In combination however, the %EE dropped to 39%. When used as sole lipid, TO or BW formed nanoparticles with comparatively higher enthalpies, 21.1 and 23.3 J/g respectively, which subsequently caused significantly higher degree of AmB expulsion, 81 and 83% respectively, whilst only 11.8% was expelled from a binary TO/BW mixture. A tertiary TO/BW/OA mixture registered the lowest enthalpy at 8.07 J/g and expelled 12.6% of AmB but encapsulated only 22% of AmB. In conclusion, nanoparticles made from equal concentrations of TO and BW produced the most desirable properties and worthy of further investigations.
  8. Tan SLJ, Billa N
    Pharmaceutics, 2021 Oct 31;13(11).
    PMID: 34834232 DOI: 10.3390/pharmaceutics13111817
    Gastrointestinal absorption remains indispensable in the systemic delivery of most drugs, even though it presents several challenges that, paradoxically, may also provide opportunities that can be exploited to achieve maximal bioavailability. Drug delivery systems made from nanoparticle carriers and especially, lipid carriers, have the potential to traverse gastrointestinal barriers and deploy in the lymphatic pathway, which aptly, is free from first pass via the liver. Several poorly soluble drugs have presented improved systemic bioavailability when couriered in lipid nanoparticle carriers. In this review, we propose an additional frontier to enhancing the bioavailability of poorly soluble drugs when encapsulated in lipid nano-carriers by imparting muco-adhesion to the particles through application of appropriate polymeric coating to the lipid carrier. The combined effect of gastrointestinal muco-adhesion followed by lymphatic absorption is a promising approach to improving systemic bioavailability of poorly soluble drugs following oral administration. Evidence to the potential of this approach is backed-up by recent studies within the review.
  9. Tan JSL, Roberts C, Billa N
    J Biomater Sci Polym Ed, 2020 02;31(2):141-154.
    PMID: 31612804 DOI: 10.1080/09205063.2019.1680926
    Oral delivery of amphotericin B (AmpB) is desirable because it provides a more patient-friendly mode of administration compared to the current delivery approach akin with the marketed AmpB formulations. The goal of the study was to investigate the pharmacokinetics and tissue distribution of orally administered chitosan-coated AmpB-loaded nanostructured lipid carriers (ChiAmpB NLC) administered to Sprague Dawley rats at a dose of 15 mg/kg. Orally administered ChiAmpB NLC resulted in a two-fold increase in the area under the curve (AUC0-∞) compared to the uncoated AmpB NLC and marketed Amphotret®. This enhanced bioavailability of AmpB suggests prolonged transit and retention of ChiAmpB NLC within the small intestine through mucoadhesion and subsequent absorption by the lymphatic pathway. The results show that mean absorption and residence times (MAT & MRT) were significantly higher from ChiAmpB NLC compared to the other two formulations, attesting to the mucoadhesive effect. The ChiAmpB NLC presented a lower nephrotic accumulation with preferential deposition in liver and spleen. Thus, the limitations of current marketed IV formulations of AmpB are potentially addressed with the ChiAmpB NLC in addition to utilizing this approach for targeting internal organs in visceral leishmaniasis.
  10. Tan CS, Billa N, Roberts CJ, Scurr DJ
    Nanomaterials (Basel), 2014 Dec 19;4(4):905-916.
    PMID: 28344257 DOI: 10.3390/nano4040905
    An amphotericin B-containing (AmB) solid lipid nanoparticulate drug delivery system intended for oral administration, comprised of bee's wax and theobroma oil as lipid components was formulated with the aim to ascertain the location of AmB within the lipid matrix: (a) a homogenous matrix; (b) a drug-enriched shell; or (c) a drug enriched core. Both the drug-loaded and drug-free nanoparticles were spherical with AmB contributing to an increase in both the z-average diameter (169 ± 1 to 222 ± 2 nm) and zeta potential (40.8 ± 0.9 to 50.3 ± 1.0 mV) of the nanoparticles. A maximum encapsulation efficiency of 21.4% ± 3.0%, corresponding to 10.7 ± 0.4 mg encapsulated AmB within the lipid matrix was observed. Surface analysis and electron microscopic imaging indicated that AmB was dispersed uniformly within the lipid matrix (option (a) above) and, therefore, this is the most suitable of the three models with regard to modeling the propensity for uptake by epithelia and release of AmB in lymph.
  11. Siddiqui NA, Billa N, Roberts CJ, Asantewaa Osei Y
    Pharmaceutics, 2016 Oct 08;8(4).
    PMID: 27740594
    Boronic acids have been widely investigated for their potential use as glucose sensors in glucose responsive polymeric insulin delivery systems. Interactions between cyclic diols and boronic acids, anchored to polymeric delivery systems, may result in swelling of the delivery system, releasing the drug. In this study, 4-formylphenylboronic acid conjugated chitosan was formulated into insulin containing nanoparticles via polyelectrolyte complexation. The nanoparticles had an average diameter of 140 ± 12.8 nm, polydispersity index of 0.17 ± 0.1, zeta potential of +19.1 ± 0.69 mV, encapsulation efficiency of 81% ± 1.2%, and an insulin loading capacity of 46% ± 1.8% w/w. Changes in size of the nanoparticles and release of insulin were type of sugar- and concentration-dependent. High concentration of diols resulted in a sustained release of insulin due to crosslink formation with boronic acid moieties within the nanoparticles. The formulation has potential to be developed into a self-regulated insulin delivery system for the treatment of diabetes.
  12. Siddiqui NA, Billa N, Roberts CJ
    J Biomater Sci Polym Ed, 2017 Jun;28(8):781-793.
    PMID: 28278045 DOI: 10.1080/09205063.2017.1301774
    The principal challenge for the use of boronic acids (BA) as glucose sensors is their lack of specificity for glucose. We examined the selectivity of and insulin release from two boronic acids- (2-formyl-3-thienylboronic acid (FTBA) and 4-formylphenylboronic acid (FPBA)) conjugated chitosan scaffolds to glucose and fructose. Adsorption of glucose to BA: chitosan conjugates was dose-dependent up to 1:1 at 35 and 42% for FPBA and FTBA respectively but the FTBA conjugates adsorbed more glucose and fructose at respective FPBA ratios. The affinity of both BA conjugates to glucose decreased with increase in BA ratio. On the other hand, the affinity of both BA conjugates for fructose decreased from ratio 1:1 to 2:1 then rose again at 3:1. Insulin release from FPBA nanoparticles (FPBAINP) and FTBA nanoparticles (FTBAINP) were both concentration-dependent within glyceamically relevant values (1-3 mg/ml glucose and 0.002 mg/ml fructose). Furthermore, the total amounts of insulin released from FPBAINP in both the media were higher than from FTBAINP. Both FPBAINP and FTBAINP have the potential for development as a glucose-selective insulin delivery system in physiological settings.
  13. Sabra R, Billa N, Roberts CJ
    Int J Pharm, 2019 Dec 15;572:118775.
    PMID: 31678385 DOI: 10.1016/j.ijpharm.2019.118775
    In the present study, we successfully developed a cetuximab-conjugated modified citrus pectin-chitosan nanoparticles for targeted delivery of curcumin (Cet-MCPCNPs) for the treatment of colorectal cancer. In vitro analyses revealed that nanoparticles were spherical with size of 249.33 ± 5.15 nm, a decent encapsulation efficiency (68.43 ± 2.4%) and a 'smart' drug release profile. 61.37 ± 0.70% of cetuximab was adsorbed to the surface of the nanoparticles. Cellular uptake studies displayed enhanced internalization of Cet-MCPCNPs in Caco-2 (EGFR +ve) cells, which ultimately resulted in a significant reduction in cancer cell propagation. The cell cycle analysis indicated that Cet- MCPCNPs induced cell death in enhanced percentage of Caco-2 cells by undergoing cell cycle arrest in the G2/M phase. These data suggest that Cet-MCPCNPs represent a new and promising targeting approach for the treatment of colorectal cancer.
  14. Peh KK, Billa N, Yuen KH
    J Chromatogr B Biomed Sci Appl, 1997 Nov 07;701(1):140-5.
    PMID: 9389350
    A simple liquid chromatographic method using amperometric detection was developed for the determination of naltrexone in human plasma. Prior to analysis, naltrexone and the internal standard (naloxone) were extracted from plasma samples using a 9:1 mixture of chloroform and isopropyl alcohol. The mobile phase comprised 0.1 M disodium hydrogen orthophosphate (pH 3.5) and acetonitrile (85.5:14.5, v/v). Analysis was run at a flow-rate of 0.8 ml/min with the detector operating under oxidative mode at an applied potential of +0.95 V. The method is specific and sensitive with a detection limit of approximately 1 ng/ml at a signal-to-noise ratio of 3:1. Mean recovery value of the extraction procedure was about 93%, while the within day and between day coefficient of variation and percent error values of the assay method were all less than 10%. The calibration curve was linear over a concentration range of 1.5-100 ng/ml.
  15. Nograles N, Abdullah S, Shamsudin MN, Billa N, Rosli R
    J Biosci Bioeng, 2012 Feb;113(2):133-40.
    PMID: 22093752 DOI: 10.1016/j.jbiosc.2011.10.003
    Alginate, a natural polysaccharide, was explored in this study as an oral delivery vehicle of a mammalian expression vector into the murine intestinal mucosa. Alginate microspheres were produced through water-in-oil (W/O) emulsification method. Average diameter sizes of microspheres were 46.88 μm±3.07 μm with significant size reduction upon utilization of 1.0% Span80. Plasmid DNA (pDNA) carrying green fluorescent protein reporter gene (GFP), pVAX-GFP, was encapsulated within microspheres at efficiencies of 72.9 to 74.4%, carrying maximum load of 6 μg pDNA. Alginate microspheres demonstrated shrinkage in pH 1.2 and swelling in pH 9.0 with pDNA release about twice the amount released in acidic environment. Oral delivery of pVAX-GFP loaded-microspheres, at 50 μg, 100 μg and 150 μg dose, was performed on BALB/c mice. Tissue biodistribution, investigated through flow cytometric analysis, demonstrated GFP positive intestinal cells (<1.0%) with 1.3-fold higher levels for the 100 μg dose; therefore suggesting feasibility of the approach for oral gene delivery and vaccination.
  16. Nair RS, Morris A, Billa N, Leong CO
    AAPS PharmSciTech, 2019 Jan 10;20(2):69.
    PMID: 30631984 DOI: 10.1208/s12249-018-1279-6
    Curcumin-loaded chitosan nanoparticles were synthesised and evaluated in vitro for enhanced transdermal delivery. Zetasizer® characterisation of three different formulations of curcumin nanoparticles (Cu-NPs) showed the size ranged from 167.3 ± 3.8 nm to 251.5 ± 5.8 nm, the polydispersity index (PDI) values were between 0.26 and 0.46 and the zeta potential values were positive (+ 18.1 to + 20.2 mV). Scanning electron microscopy (SEM) images supported this size data and confirmed the spherical shape of the nanoparticles. All the formulations showed excellent entrapment efficiency above 80%. FTIR results demonstrate the interaction between chitosan and sodium tripolyphosphate (TPP) and confirm the presence of curcumin in the nanoparticle. Differential scanning calorimetry (DSC) studies of Cu-NPs indicate the presence of curcumin in a disordered crystalline or amorphous state, suggesting the interaction between the drug and the polymer. Drug release studies showed an improved drug release at pH 5.0 than in pH 7.4 and followed a zero order kinetics. The in vitro permeation studies through Strat-M® membrane demonstrated an enhanced permeation of Cu-NPs compared to aqueous curcumin solution (p ˂ 0.05) having a flux of 0.54 ± 0.03 μg cm-2 h-1 and 0.44 ± 0.03 μg cm-2 h-1 corresponding to formulations 5:1 and 3:1, respectively. The cytotoxicity assay on human keratinocyte (HaCat) cells showed enhanced percentage cell viability of Cu-NPs compared to curcumin solution. Cu-NPs developed in this study exhibit superior drug release and enhanced transdermal permeation of curcumin and superior percentage cell viability. Further ex vivo and in vivo evaluations will be conducted to support these findings.
  17. Nair RS, Billa N, Leong CO, Morris AP
    Pharm Dev Technol, 2021 Feb;26(2):243-251.
    PMID: 33274672 DOI: 10.1080/10837450.2020.1860087
    Tocotrienol (TRF) ethosomes were developed and evaluated in vitro for potential transdermal delivery against melanoma. The optimised TRF ethosomal size ranged between 64.9 ± 2.2 nm to 79.6 ± 3.9 nm and zeta potential (ZP) between -53.3 mV to -62.0 ± 2.6 mV. Characterisation of the ethosomes by ATR-FTIR indicated the successful formation of TRF-ethosomes. Scanning electron microscopy (SEM) images demonstrated the spherical shape of ethosomes, and the entrapment efficiencies of all the formulations were above 66%. In vitro permeation studies using full-thickness human skin showed that the permeation of gamma-T3 from the TRF ethosomal formulations was significantly higher (p 
  18. Nair RS, Billa N, Mooi LY, Morris AP
    Pharm Dev Technol, 2022 Jan 06.
    PMID: 34957920 DOI: 10.1080/10837450.2021.2023568
    This study aimed at developing curcumin nanoethosomes (Cur-Ets) with superior skin permeation intended for melanoma treatment. Although curcumin is active against many types of skin cancers, a suitable topical formulation is still lacking due to its hydrophobicity and poor skin permeation. The formulation was characterized using Scanning Transmission Electron Microscopy (STEM), atomic force microscopy (AFM), ATR-FTIR, DSC and XRD. In vitro skin permeation was carried out using human skin, and the cytotoxicity of the formulation was evaluated on human melanoma cells (SK-MEL28). The vesicle size and zeta potential of the Cur-Ets were determined as 67 ± 1.6 nm and -87.3 ± 3.3 mV, respectively. STEM and AFM analysis further support the size and morphology of the formulation. Curcumin's compatibility with formulation additives was confirmed by ATR-FTIR analysis. In addition, DSC and XRD analyses showed successful drug encapsulation in nanoethosomes. The drug encapsulation efficiency was determined as 87 ± 0.9%. The skin permeation of curcumin from Cur-Ets showed a superior flux (0.14 ± 0.03 µg cm-2 h-1) compared to the control (p 
  19. Ling Tan JS, Roberts CJ, Billa N
    Pharm Dev Technol, 2019 Apr;24(4):504-512.
    PMID: 30132723 DOI: 10.1080/10837450.2018.1515225
    This study describes the properties of an amphotericin B-containing mucoadhesive nanostructured lipid carrier (NLC), with the intent to maximize uptake within the gastrointestinal tract. We have reported previously that lipid nanoparticles can significantly improve the oral bioavailability of amphotericin B (AmpB). On the other hand, the aggregation state of AmpB within the NLC has been ascribed to some of the side effects resulting from IV administration. In the undissolved state, AmpB (UAmpB) exhibited the safer monomeric conformation in contrast to AmpB in the dissolved state (DAmpB), which was aggregated. Chitosan-coated NLC (ChiAmpB NLC) presented a slightly slower AmpB release profile as compared to the uncoated formulation, achieving 26.1% release in 5 hours. Furthermore, the ChiAmpB NLC formulation appeared to prevent the expulsion of AmpB upon exposure to simulated gastrointestinal pH media, whereby up to 63.9% of AmpB was retained in the NLC compared to 56.1% in the uncoated formulation. The ChiAmpB NLC demonstrated mucoadhesive properties in pH 5.8 and 6.8. Thus, the ChiAmpB NLC formulation is well-primed for pharmacokinetic studies to investigate whether delayed gastrointestinal transit may be exploited to improve the systemic bioavailability of AmpB, whilst simultaneously addressing the side-effect concerns of AmpB.
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