Formulation and Evaluation of Arbutin Emulgel: A Novel Approach to Combat Hyperpigmentation

 Corresponding author: Vaishnavi Dnyaneshwar Langhe. Copyright © 2025 Author(s) retain the copyright of this article. This article is published under the terms of the Creative Commons Attribution License 4.0. Formulation and Evaluation of Arbutin Emulgel: A Novel Approach to Combat Hyperpigmentation Vaishnavi Dnyaneshwar Langhe *, Reema Chandrakant Londhe, Shubham Chandrakant Gadge, Prachi Nandkumar Padwal and Pooja Sampat Lamkhade Student, Samarth Institute of Pharmacy, Belhe, Pune, Maharashtra, India. World Journal of Biology Pharmacy and Health Sciences, 2025, 24(01), 448-454 Publication history: Received on 10 September 2025; revised on 26 October 2025; accepted on 29 October 2025 Article DOI: https://doi.org/10.30574/wjbphs.2025.24.1.0908 Abstract Hyperpigmentation, a prevalent dermatological concern characterized by localized or generalized darkening of the skin, significantly impacts an individual's aesthetic appearance and psychological well-being. Current therapeutic strategies often present limitations such as side effects, poor efficacy, or stability issues. Arbutin, a natural hydroquinone derivative, is recognized for its potent tyrosinase inhibitory activity, making it a promising depigmenting agent. However, its poor skin penetration and stability in conventional topical formulations hinder its therapeutic potential. This review article explores the rationale behind developing arbutin emulgel as a novel approach to overcome these challenges. Emulgels , hybrid systems combining the advantages of emulsions and gels, offer enhanced drug permeation, controlled release, and improved patient compliance due to their non-greasy and easily spreadable nature. This article delves into the mechanism of arbutin's action, factors influencing hyperpigmentation treatment, detailed profiles of key ingredients, comprehensive methodology for emulgel preparation, and critical evaluation parameters including physicochemical, in vitro, ex vivo, and in vivo assessments. The aim is to highlight the potential of arbutin emulgel as an effective, stable, and patient-friendly topical delivery system for combating hyperpigmentation. Keywords: Arbutin; Emulgel; Hyperpigmentation; Tyrosinase inhibitor; Topical drug delivery; Skin lightening; Formulation; Evaluation 1. Introduction Hyperpigmentation encompasses a range of skin conditions marked by an increase in melanin production, leading to darker patches on the skin. These conditions, including melasma, post-inflammatory hyperpigmentation (PIH), solar lentigines (age spots), and freckles, are triggered by various factors such as excessive sun exposure, hormonal fluctuations, inflammation, genetic predisposition, and certain medications. Beyond the physical manifestation, hyperpigmentation can lead to significant psychological distress, affecting self-esteem and quality of life. The quest for effective and safe depigmenting agents has led to the development of numerous topical treatments. Historically, hydroquinone has been the gold standard, but concerns regarding its potential for chronosis, irritation, and cytotoxicity have prompted the search for safer alternatives. Other agents like retinoids, azelaic acid, kojic acid, and vitamin C offer varying degrees of efficacy but often come with their own set of limitations, including instability, poor skin penetration, or mild irritation. Arbutin (4-hydroxyphenyl-β-D-glucopyranoside) emerges as a compelling alternative. Derived from natural sources like bearberry (Arctostaphylos uva-ursi), arbutin is a glycosylated hydroquinone that acts as a competitive inhibitor of tyrosinase, a crucial enzyme in melanogenesis. Its glycosidic bond renders it more stable and less irritating than World Journal of Biology Pharmacy and Health Sciences, 2025, 24(01), 448-454 449 hydroquinone, as it slowly releases hydroquinone in situ within the skin. Despite its advantages, arbutin's hydrophilic nature and relatively large molecular size contribute to poor skin penetration, limiting its therapeutic efficacy when delivered via conventional creams or lotions. Furthermore, its stability can be compromised by light, heat, and pH variations. To overcome these challenges, novel drug delivery systems are imperative. Emulgels represent a promising approach, combining the benefits of both emulsions and gels. They are essentially emulsions (oil-in-water or water-in-oil) incorporated into a gel base. This hybrid system offers enhanced drug solubilization, improved skin permeation due to the presence of an oil phase, controlled release characteristics, and superior patient compliance owing to their nongreasy, easily spreadable, and cooling properties. This review aims to comprehensively discuss the formulation and evaluation of arbutin emulgel as a novel and effective strategy to combat hyperpigmentation. 2. Mechanism of treatment The primary mechanism by which arbutin combats hyperpigmentation is through the inhibition of tyrosinase, a coppercontaining enzyme that catalyses two key steps in melanin biosynthesis: • Hydroxylation of L-tyrosine to L-DOPA (3,4-dihydroxyphenylalanine) • Oxidation of L-DOPA to DOPA quinone. Arbutin acts as a competitive inhibitor of tyrosinase. Its structural similarity to L-tyrosine allows it to bind to the active site of the enzyme, thereby preventing L-tyrosine from binding and initiating the melanogenesis pathway. Unlike hydroquinone, which can be cytotoxic to melanocytes at higher concentrations, arbutin is considered a safer alternative because it is a pro-drug. It is hydrolysed by skin enzymes (β-glucosidases) to release hydroquinone gradually and locally, minimizing systemic exposure and reducing the risk of irritation and cytotoxicity. The emulgel formulation further enhances this mechanism by: • Improving Skin Penetration: The emulsion component, particularly the oil phase, can disrupt the lipid bilayers of the stratum corneum, facilitating the deeper penetration of arbutin. Penetration enhancers incorporated into the emulgel also contribute to this. • Sustained Release: The gel matrix provides a reservoir for the drug, allowing for a more sustained release of arbutin over time, which can prolong its therapeutic effect and reduce the frequency of application. • Enhanced Stability: The gel structure can protect arbutin from degradation factors like light and oxidation, ensuring that a higher concentration of the active ingredient remains available for action. 3. Factors affecting treatment Several factors can influence the efficacy and outcome of hyperpigmentation treatment with arbutin emulgel: • Type and Severity of Hyperpigmentation: Different types of hyperpigmentation (e.g., melasma, PIH, freckles) respond differently to treatment. Deeper dermal pigmentation is generally harder to treat than epidermal pigmentation. • Patient's Skin Type (Fitzpatrick Scale): Individuals with darker skin types (IV-VI) are more prone to hyperpigmentation and may require longer treatment durations or different concentrations. They also have a higher risk of post-inflammatory hyperpigmentation. • Sun Exposure: Continued exposure to UV radiation is a major trigger for melanin production. Strict sun protection (sunscreen, protective clothing) is crucial for treatment success and preventing recurrence. • Hormonal Factors: For conditions like melasma, hormonal influences (pregnancy, oral contraceptives) can make treatment challenging and increase the likelihood of recurrence. • Inflammation: Underlying inflammation or irritation can exacerbate hyperpigmentation. The emulgel formulation should be non-irritating to avoid triggering PIH. • Compliance: Consistent and correct application of the emulgel is vital for achieving desired results. • Formulation Characteristics: The concentration of arbutin, the type and concentration of gelling agents, emulsifiers, and penetration enhancers, as well as the overall stability and release profile of the emulgel, directly impact its therapeutic efficacy. • Individual Variability: Genetic factors, skin barrier function, and metabolic rates can lead to variations in individual responses to treatment. World Journal of Biology Pharmacy and Health Sciences, 2025, 24(01), 448-454 450 4. Drug profile: arbutin • Chemical Name: 4-hydroxyphenyl-β-D-glucopyranoside • Molecular Formula: C{12}H{16}O7 • Molecular Weight: 272.25 g/mol • Source: Naturally occurring in various plants, notably bearberry (Arctostaphylos uva-ursi), cranberry, and blueberry leaves. • Appearance: White crystalline powder. • Solubility: Freely soluble in water, alcohol, and propylene glycol; sparingly soluble in ether and chloroform. • Mechanism of Action: Competitive inhibition of tyrosinase enzyme, thereby reducing melanin synthesis. • Stability: Relatively stable compared to hydroquinone, but susceptible to hydrolysis (releasing hydroquinone) under acidic conditions or in the presence of β-glucosidase enzymes. Sensitive to light and heat. • Pharmacokinetics: Poor skin penetration due to its hydrophilic nature and relatively large molecular size. • Safety Profile: Generally considered safe for topical use with a lower incidence of irritation and sensitization compared to hydroquinone. 5. Ingredients profile The successful formulation of arbutin emulgel relies on a careful selection of excipients, each playing a critical role: • Gelling Agents (for the gel phase): o Carbopol (Carbomer): Synthetic polymers widely used for their excellent gelling properties, pseudoplastic flow, and ability to form clear gels. Requires neutralization (e.g., with triethanolamine) to form a gel. o Hydroxypropyl Methylcellulose (HPMC): A semi-synthetic polymer, non-ionic, provides good viscosity and film-forming properties. Less sensitive to pH changes than Carbopol. • Oil Phase (for the emulsion): o Light Liquid Paraffin: Providing occlusive properties and a smooth feel. o Natural Oils (Almond oil): Can be included for their emollient and skin-conditioning properties, though their stability in emulsion needs careful consideration. • Emulsifiers (to stabilize the emulsion): o Non-ionic Surfactants: Generally preferred for topical formulations due to lower irritation potential. o Span 80: Lipophilic, low HLB (Hydrophilic-Lipophilic Balance) values, used in W/O emulsions or as coemulsifiers. o Tween 80: Hydrophilic, high HLB values, used in O/W emulsions. • Aqueous Phase: o Purified Water: The main solvent for hydrophilic components and the continuous phase of O/W emulsions. • Penetration Enhancers: o Propylene Glycol (PG): Humectants that also aid in drug solubilization and penetration. • Preservatives: o Phenoxyethanol: A widely used preservative with good efficacy against bacteria and fungi. • Antioxidants: o Tocopherol (Vitamin E): Natural antioxidant. • pH Adjusters: o Triethanolamine (TEA): Used to neutralize Carbopol gels and adjust pH. 5.1. Equipment • pH meter for adjusting emulgel pH. • Magnetic stirrer for uniform emulgel mixing. • Analytical balance for precise measurements. • Sterile containers for emulgel storage. 6. Method of preparation The development of arbutin emulgel involves a systematic approach, typically divided into preparation and evaluation phases. World Journal of Biology Pharmacy and Health Sciences, 2025, 24(01), 448-454 451 The general procedure for preparing an arbutin emulgel involves two main steps: preparing the emulsion and preparing the gel, followed by their incorporation. • Preparation of Emulsion o Oil Phase: The oil-soluble ingredients oil, lipophilic emulsifiers like Span 80, antioxidants are weighed and heated to approximately 70-75°C to ensure complete melting and mixing. o Aqueous Phase: The water-soluble ingredients purified water, hydrophilic emulsifiers like Tween 80, arbutin, preservatives, humectants are weighed and heated to the same temperature (70-75°C). o Emulsification: The heated aqueous phase is slowly added to the heated oil phase under continuous high-speed stirring using homogenizer until a uniform emulsion is formed. o Cooling: The emulsion is then allowed to cool gradually to room temperature with continuous stirring to ensure stability and prevent phase separation. • Preparation of Gel Base o Hydration: The gelling agent Carbopol is slowly dispersed in a portion of purified water under continuous stirring to avoid lump formation. It is allowed to hydrate completely, typically for several hours or overnight, to form a uniform dispersion. o Neutralization: For Carbopol gels, a neutralizing agent triethanolamine is added dropwise to the dispersion with continuous stirring until the desired gel consistency and pH are achieved. o Other Additives: Any remaining water-soluble excipients additional preservatives, penetration enhancers can be incorporated into the gel base. • Incorporation of Emulsion into Gel Base o The prepared emulsion (at room temperature) is slowly and carefully incorporated into the prepared gel base under continuous, gentle stirring. o The mixture is stirred until a homogeneous emulgel is formed, ensuring uniform distribution of the emulsion droplets within the gel matrix. o The final pH of the emulgel is adjusted to be skin-compatible (typically 4.5-6.5) using appropriate pH adjusters. 7. Evaluation parameters The formulated arbutin emulgel undergoes a series of rigorous evaluation tests to ensure its quality, stability, safety, and efficacy. 7.1. Physicochemical Evaluation • Organoleptic Propertieso Color: White o Clarity: Clear o Odor: Odorless o Texture: Smooth • pH Measurement: Using a calibrated pH meter to ensure the pH is within the physiological range of the skin to prevent irritation. It was found 6.3. • Viscosity: Measured using a viscometer i.e. Brookfield viscometer to assess the flow properties and consistency, which impacts spreadability and retention on the skin. • Spreadability: Determined by measuring the diameter of a spread circle of a known weight of emulgel between two glass plates. Good spreadability is crucial for patient compliance. • Extrudability: Assessed by measuring the amount of emulgel extruded from a tube under specific pressure, indicating ease of application. • Drug Content/Assay: Quantitative analysis of arbutin in the emulgel using validated analytical methods like High-Performance Liquid Chromatography (HPLC) to ensure uniform drug distribution and accurate dosing. • Globule Size and Zeta Potential: For the emulsion component, globule size analysis (e.g., dynamic light scattering) determines the size distribution of oil droplets, which affects stability. Zeta potential measures the surface charge of the droplets, indicating electrostatic repulsion and emulsion stability. • Homogeneity: Visual inspection for the absence of lumps or aggregates, ensuring uniform distribution of ingredients. • Refractive Index: Measured using a refractometer to check for consistency and potential changes during stability studies. World Journal of Biology Pharmacy and Health Sciences, 2025, 24(01), 448-454 452 7.2. In Vitro Studies • Vitro Drug Release Studies: Conducted using Franz diffusion cells with a synthetic membrane (e.g., cellophane, cellulose acetate). The emulgel is applied to the donor compartment, and the amount of arbutin released into the receptor compartment over time is quantified. This provides information on the release kinetics of the drug from the formulation. • In Vitro Skin Permeation Studies: Similar to release studies but using excised animal skin (e.g., rat, pig ear skin) or human cadaver skin. This assesses the amount of arbutin that penetrates into and permeates through the skin layers, providing a more realistic indication of bioavailability. 7.3. Stability Studies • Accelerated Stability Testing: Emulgel samples are stored at elevated temperatures (e.g., 40°C ± 2°C) and humidity (e.g., 75% RH ± 5% RH) for a specified period (e.g., 3 or 6 months) to predict long-term stability. • Long-Term Stability Testing: Samples are stored at room temperature (e.g., 25°C ± 2°C, 60% RH ± 5% RH) for 12-24 months. • Freeze-Thaw Cycles: Samples are subjected to alternating cycles of freezing (e.g., -5°C) and thawing (e.g., 25°C) to assess physical stability 7.4. Ex Vivo Studies • Skin Irritation Potential: Using excised animal or human skin, the emulgel is applied, and histological examination or measurement of inflammatory markers can assess potential irritation or sensitization. • Cytotoxicity Studies: On relevant skin cell lines (e.g., melanocytes, keratinocytes) to evaluate the safety of the formulation and its components at the cellular level. 7.5. Skin Irritation and Sensitization Patch tests on healthy human volunteers to assess dermal safety, looking for erythema, edema, or other signs of irritation. 7.6. Efficacy Studies: • Melanin Index: Using a mexameter or similar device to objectively quantify changes in melanin content in hyperpigmented areas before and after treatment. • Skin Brightness (L value): Using a chromameter to measure changes in skin lightness (L* value in the Lab* color space). An increase in L* value indicates skin lightening. • Clinical Photography: Standardized digital photographs taken under controlled lighting conditions to visually document the reduction in hyperpigmentation. • Patient Self-Assessment: Questionnaires to gather subjective feedback from patients regarding perceived efficacy, satisfaction, and adverse effects. • Safety Studies: Monitoring for any adverse effects such as erythema, itching, dryness, or allergic reactions during the course of treatment. 8. Conclusion The formulation and evaluation of arbutin emulgel represent a significant advancement in the topical treatment of hyperpigmentation. By combining the depigmenting efficacy of arbutin with the superior delivery characteristics of an emulgel system, this approach effectively addresses the limitations of conventional formulations, particularly poor skin penetration and stability. The emulgel's ability to enhance arbutin's bioavailability, provide controlled release, and offer a cosmetically elegant, patient-friendly application makes it a promising candidate for clinical use. Rigorous physicochemical, in vitro, ex vivo, and in vivo evaluations are crucial to ensure the safety, stability, and therapeutic efficacy of the developed formulation. The collective evidence suggests that arbutin emulgel holds substantial potential as a novel and effective strategy to combat various forms of hyperpigmentation, offering a safer and more efficient alternative to existing treatments. Result We performed the formulation and development of arbutin emulgel which is depigmenting formulation. We also studied the various evaluation parameters , it was found very effective. World Journal of Biology Pharmacy and Health Sciences, 2025, 24(01), 448-454 453 Future aspects While arbutin emulgel shows great promise, several avenues for future research and development exist: • Optimization of Arbutin Derivatives: Further investigation into the use of alpha-arbutin, deoxy arbutin, or other novel arbutin derivatives within emulgel systems, which may offer enhanced stability and efficacy. • Nanoemulgels and Microemulgels: Exploring the development of nanoemulgels or microemulgels to further reduce globule size, potentially leading to even greater skin penetration and bioavailability of arbutin. • Combination Therapies: Investigating the synergistic effects of combining arbutin with other depigmenting agents (e.g., kojic acid, vitamin C, niacinamide) or penetration enhancers within the emulgel formulation to achieve superior results. • Natural Extracts: Incorporating natural extracts with known antioxidant or anti-inflammatory properties into the emulgel to provide additional benefits and enhance overall skin health. • Long-Term Clinical Trials: Conducting larger-scale, long-term clinical trials with diverse patient populations to establish the sustained efficacy, safety, and recurrence rates of arbutin emulgel in various hyperpigmentation conditions. • Mechanism of Action at Cellular Level: Deeper studies into the cellular and molecular mechanisms of arbutin emulgel's action, including its effects on melanocyte viability, melanosome transfer, and gene expression related to melanogenesis. • Stability Enhancement: Developing advanced strategies to further improve the photostability and chemical stability of arbutin within the emulgel, possibly through encapsulation or novel antioxidant combinations. • Personalized Medicine: Exploring the potential for personalized arbutin emulgel formulations tailored to individual skin types and specific hyperpigmentation conditions. Compliance with ethical standards Acknowledgement We sincerely acknowledge the continuous guidance, motivation, and constructive feedback provided by our mentor, Prof. Reema Chandrakant Londe. Their expertise and patience have been instrumental in shaping this review paper. We also extend our gratitude to Samarth Institute of Pharmacy Belhe for providing the necessary academic environment and resources that supported this work. References [1] I.A. Ahmed, M.A. Mikail, N. Zamakshshari, A.-S.H. Abdullah, Natural anti-aging skincare: role and potential, Biogerontology 21 (3) (2020) 293–310. [2] P. Burger, A. Landreau, S. Azoulay, T. Michel, X. Fernandez, Skin whitening cosmetics: feedback and challenges in the development of natural skin lighteners, Cosmetics 3 (4) (2016) 36. [3] N. Masub, A. Khachemoune, Cosmetic skin lightening use and side effects, J. Dermatol. Treat. 33 (3) (2022) 1287– 1292. [4] A.M. Thawabteh, A. Jibreen, D. Karaman, A. Thawabteh, R. Karaman, Skin pigmentation types, causes and treatment—a review, Molecules 28 (12) (2023) 4839. [5] V. Rizzi, J. Gubitosa, P. Fini, P. Cosma, Neurocosmetics in skincare—the fascinating world of skin–brain connection: a review to explore ingredients, commercial products for skin aging, and cosmetic regulation, Cosmetics 8 (3) (2021) 66. [6] A. Nautiyal, S. Wairkar, Management of hyperpigmentation: current treatments and emerging therapies, Pigm. Cell Melanoma Res. 34 (6) (2021) 1000–1014. [7] S. Moolla, Y. Miller-Monthrope, Dermatology: how to manage facial hyperpigmentation in skin of colour, Drugs Context 11 (2022). [8] I.A. Ahmed, M.A. Mikail, N.H. Zamakshshari, M.R. Mustafa, N.M. Hashim, R. Othman, Trends and challenges in phytotherapy and phytocosmetics for skin aging, Saudi J. Biol. Sci. 29 (8) (2022) 103363. [9] L. Nahar, A. Al-Groshi, A. Kumar, S.D. Sarker, Arbutin: occurrence in plants, and its potential as an anticancer agent, Molecules 27 (24) (2022) 8786. World Journal of Biology Pharmacy and Health Sciences, 2025, 24(01), 448-454 454 [10] P. Mishra, F. Ahsan, T. Mahmood, S. Bano, A. Shamim, V.A. Ansari, J. Yadav, Progress [11] Bhatt P, Gnanarajan G. Emulgels: A novel formulation approach for topical delivery of hydrophobic drugs. International research journal of pharmacy. 2013;4(2):12-6. [12] Bonacucina G, Cespi M, Palmieri GF. Characterization and stability of emulsion gels based on acrylamide/sodium acryloyldimethyl taurate copolymer. Aaps Pharmscitech. 2009;10(2):368-75. [13] Brahmankar D, Jaiswal SB. Biopharmaceutics and pharmacokinetics: A treatise: Vallabh prakashan; 2005. [14] Brown MB, Jones SA. Hyaluronic acid: a unique topical vehicle for the localized delivery of drugs to the skin. Journal of the European Academy of Dermatology and Venereology. 2005;19(3):308-18. [15] Brown TM, Krishnamurthy K. Histology, dermis. StatPearls [Internet]. 2020. [16] Burki IK, Khan MK, Khan BA, Uzair B, Braga VA, Jamil QA. Formulation development, characterization, and evaluation of a novel dexibuprofencapsaicin skin emulgel with improved in vivo anti-inflammatory and analgesic effects. AAPS PharmSciTech. 2020;21(6):1-14. [17] Caillett-Bois F, Rault I, Steiger M. Topical composition. Google Patents; 2010. [18] Charoenrein S, Tatirat O, Rengsutthi K, Thongngam M. Effect of konjac glucomannan on syneresis, textural properties and the microstructure of frozen rice starch gels. Carbohydrate polymers. 2011;83(1):291-6. [19] Charyulu NR, Joshi P, Dubey A, Shetty A. Emulgel: A Boon for Enhanced Topical Drug Delivery. Journal of Young Pharmacists. 2021;13(1):76. [20] Dadwal A, Mishra N, Rawal RK, Narang RK. Development and characterisation of clobetasol propionate loaded Squarticles as a lipid nanocarrier for treatment of plaque psoriasis. Journal of microencapsulation. 2020;37(5):341-54.of arbutin from dietary supplement to advanced medicine, eFood 5 (6) (2024) e70013 [21] Baibhav J, Gurpreet S, Rana A.C, Seema S, Vikas S. Emulgel: a comprehensive review on the recent advances in topical drug delivery. Int Res J Pharm. 2011;2(11):66-70. [22] Wesley Z. Souza D, Rajashree G. Formulation: design, development and evaluation of emulgel for topical delivery of meloxicam in the treatment of rheumatoid arthritis. Indo Am J Pharm Res. 2015;5(3):1721-1729. [23] Hayder Kadhim Drais. Development, characterization and evaluation of the piroxicam nanoemulsion gel as topical dosage form. WJPPS. 2015;5(6):308-318. [24] Krishnaveni M, Sujatha B, Yanadaiah P, Sreenivasulu M, Venkata Anudeep P. A study on the effect of penetration enhancer on ketoprofen emulgel. Int J Res Pharm Life Sci. 2015;3(2):346-351 [25] Kim J, De Jesus O. Medication Routes of Administration. [Updated 2023 Feb 12]. In: Stat Pearls. Treasure Island (FL): StatPearls Publishing; 2023 Jan. Available from: https://www.ncbi.nlm.nih.gov/books/NBK568677/ [26] https://www.drugs.com/search.php?searchterm=emul gel [27] Gusai T, Dhavalkumar M, Soniwala M, Dudhat K, Vasoya J, Chavda J. Formulation and optimization of microsponge-loaded emulgel to improve the transdermal application of acyclovir-a DOE based approach. Drug Deliv Transl Res. 2021;11(5):20092029. [28] de Oliveira Neto AS, Souza ILA, Amorim MES, de Freitas Souza T, Rocha VN, do Couto RO, Fabri RL, de Freitas Araújo MG. Antifungal efficacy of atorvastatin-containing emulgel in the treatment of oral and vulvovaginal candidiasis. Med Mycol. 2021;59(5):476-485. [29] Sabry HS, Al-Shohani ADH, Mahmood SZ. Formulation and Evaluation of Levofloxacin and Betamethasone Ophthalmic Emulgel. J Pharm Bioallied Sci. 2021;13(2):205-211. [30] Mohamad M. Optimization of chlorphenesin emulgel formulation. Am Assoc Pharm Sci J. 2014;6(3):1-5.