Nigerian Journal of Pharmaceutical Research

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1 Nigerian Journal of Pharmaceutical Research Vol. 7, No. 1, (September 2008) QUALITY EVALUATION OF SOME BRANDS OF VITAMIN C PREPARATIONS J.O. Soyinka 1,*, F.J. Faleye 2 and G.E. Adetogun 3 Departments of 1 Pharmaceutical Chemistry and 3 Pharmaceutics, Faculty of Pharmacy, Obafemi Awolowo University, Ile-Ife, 2 Department of Chemistry, University of Ado-Ekiti, Ekiti State, Nigeria. Abstract Ten brands each, of vitamin C tablets and syrups were evaluated for their quality using British pharmacopeia colorimetric and titrimetric analytical methods. Other characteristics assessed were uniformity of weight, friability, disintegration and dissolution rate. Sixty percent of the tablet and 40 % of the syrup brands had values within the BP specified range and were therefore chemically equivalent. The percentages of the tablet brands that complied with the official specifications for friability, disintegration and uniformity of weight tests were 100, 100 and 60 %, respectively. Seventy percent of the brands had above 70 % dissolution at less than 45 min. while 30 % failed to attain 70 % dissolution throughout the period of the determination. Although sixty percent of vitamin C tablet brands had ascorbic acid contents within the pharmacopoeial limits, some of these brands failed the dissolution profile and weight uniformity tests, indicating that they were substandard with consequent therapeutic failure. Therefore, in ascertaining quality of the brands of drugs, assays for active constituents should be combined with assessment of other pharmaceutical characters. Keywords: Vitamin C, tablets, syrups, titrimetric method, colorimetric method, quality evaluation * : Corresponding author josandj@oauife.edu.ng Introduction Vitamin C or L-ascorbate (1) is a water-soluble vitamin that plays important role in human nutrition. It is a highly effective antioxidant and reduces oxidative stress (Padayatty et al., 2003). As an enzyme cofactor, it is important for the biosynthesis of many biochemicals such as collagen necessary for the building of blood vessels, tendons, ligaments, and bone. It is also essential for the synthesis of carnitine that is needed for the transport of fat in the production of energy (Levine et al., 2001), metabolism of cholesterol to bile acids and reduction of incidence of gallstone (Lee et al., 2001). The increased number of various brands of drugs from multiple sources in the developing countries was to improve their overall healthcare delivery systems. However, this was accompanied with increased number of fake and substandard drugs that make it difficult for healthcare providers to effectively select good products from among several brands containing the same active ingredient(s). The proprietary drugs must be identical in content, purity, uniformity of weight, disintegration and dissolution rates before they are considered chemical equivalents (Olaniyi et al., 2001). There are several reports of differences in clinical efficacies by these chemical equivalents that could only be due to the different manufacturers (Remington s Pharmaceutical Sciences, 1990). Only sixty percent of brands of ciprofloxacin tablets (Adegbolagun et al., 2007) and 38 % of pyrimethamine tablets (Odeniyi et al., 2002) were found to be chemically equivalent while the others were substandard. Most of the counterfeits detected were largely by accident. It is conservatively estimated that more The Official Publication of Nigerian Association of Pharmacists in Academia 12

2 than 10 % of the global medicine market consists of substandard (fake) drugs, with developing countries having an estimate of 25 % and in some places it could be as high as 50 % (WHO, 2006). Composition and ingredients of substandard drugs do not meet the pharmacopoeial specifications and are consequently ineffective and dangerous to the patient. Antioxidant properties and its use as an adjuvant in the management of common cold have increased the use of vitamin C. Hence, the numerous brands of vitamin C tabets and syrups circulating in Nigeria, need to be evaluated for their quality. The British Pharmacopoeia (BP) recommends titrimetric method using ammonium cerium (IV) sulphate for the tablets, and titration with iodine for both syrups and pure compound for assay of their ascorbic acid contents (BP, 2007). The quality of ten brands each of vitamin C tablets and syrups were evaluated using these two titrimetric and colorimetric methods together with other pharmaceutical tests in order to determine the level of substandard vitamin C preparations available in our market. Materials and methods Materials Vitamin C pure powder was from Novel Pharmaceutical Industry, Lagos Nigeria, while the various brands of the tablets and syrups were purchased from retail Pharmacies in Ile-Ife, Osun State, Nigeria. The tablet samples were coded T 1 - T 10 and syrups S 1 - S 10 ; both were stored at ambient temperature until needed. All chemicals used, Ethanol (96 %), sulphuric acid, ammonium cerium (IV) sulphate, ferroin solution, orthophosphoric acid, iodine, starch solution, were of analytical grade and obtained from British Drug Houses (BDH). Thin layer chromatographic identification Thin layer chromatograms of pure vitamin C (0.5 %) in water and equivalents solutions of tablets obtained with EtOH:H 2 O (6:1) as solvent system were compared using their R f values and colour characteristics under ultraviolet (254 nm). Uniformity of weight Twenty tablets from each of the ten brands were weighed individually using a Mettler 1180 weighing balance. The average weights of the tablets were calculated as well as their percentage deviation from the average weight as described in BP (2007). Friability test Twenty tablets were weighed and subjected to abrasion at 25 rev/min for 5 min, using Erweka single drum friability tester. The tablets were weighed thereafter and their percentage loss was calculated (BP, 2007). Tablet disintegration test The tablets were disintegrated at 37 C using Manesty Tablet Disintegration Test Unit TD 75T176, England until no particle remained in the basket of the system. The time taken for each of the four tablets tested in each brand to totally disintegrate was recorded (BP, 2007). Dissolution rate Six tablets per brand were rotated in the basket of Veego dissolution rate testing apparatus at 100 r.p.m and using 0.1 M HCl (900 ml) maintained at 37 ± 0.5 o C as the dissolution medium. Samples (10 ml) were withdrawn at intervals of ten minutes for 1 hour and replaced with 10 ml fresh dissolution The Official Publication of Nigerian Association of Pharmacists in Academia 13

3 medium after each sampling. The samples were filtered and diluted appropriately before their absorbances were measured at 243 nm using Ultraviolet/Visible Spectrophotometer (Perkin-Elmer model, Lambda 33). The content of Vitamin C in each sample was determined based on the calibration curve generated at λ max 243 nm. The regression equation for the calibration curve was : Y = X , r 2 = The dissolution profiles for the different brands of vitamin C tablets were generated after plotting the graph of amount of vitamin C dissolved against dissolution time. The average T 70 (time for 70 % of the active drug to be dissolved) and the amount dissolved at 45 min. were obtained for each brand (BP, 2007). Titration with 0.05 M iodine solution 20 tablets were weighed and powdered. A quantity of this powder that should contain 0.15 g of vitamin C (ascorbic acid) was dissolved in a mixture of 30 ml of water and 20 ml of 1 M sulphuric acid (H 2 SO 4 ) and titrated with 0.05 M iodine, using 1 ml of starch as indicator until a persistent violetblue colour was obtained. For the syrup, 100 ml of 1 % w/v orthophosphoric acid in water was added to a volume of the syrup that should contain 0.14 g of vitamin C and similarly titrated with 0.05 M iodine. About 0.15 g of pure ascorbic acid powder was dissolved in a mixture of 10 ml dilute H 2 SO 4 and 80 ml of CO 2 free water and was similarly titrated with 0.05 M iodine. The procedure for the pure ascorbic acid, and all brands of tablets and syrups was done in triplicates. Titration with 0.1 M ammonium cerium(iv) sulphate 20 tablets were weighed and powdered. A quantity of the powder that should contain 0.15 g of vitamin C was dissolved in a mixture of 30 ml of water and 20 ml of 1 M H 2 SO 4 and titrated with 0.1 M ammonium cerium(iv) sulphate, using ferroin solution as indicator. For the syrup, 100 ml of 1% w/v orthophosphoric acid in water was added to a volume of the syrup that should contain 0.14 g of vitamin C and similarly titrated with 0.1 M ammonium cerium(iv) sulphate. The procedure for all brands of tablets and syrups was done in triplicates. Colorimetric method The absorbance of the coloured complex formed between potassium ferricyanide solution and ascorbic acid measured at λ max 520 nm was used to plot a calibration curve against concentration of ascorbic acid ( µg/ml). The regression equation obtained from the calibration curve was used for the calculation of the amount of ascorbic acid in the samples. Statistical analysis All results obtained were subjected to statistical analysis of mean and standard deviation, using Microsoft Excel 2007 version. Results and discussion All the brands of tablets and syrups used were within their shelf-lives as at the time of study. Pure ascorbic acid had R f value of 0.65 and a similar spot was detected in all the tablet and syrup brands of vitamin C preparations. This preliminary test indicated that all the preparations contained the active ingredient, vitamin C. Four brands (T 2, T 5, T 7, T 8 ) did not comply with the BP (2007) specifications The Official Publication of Nigerian Association of Pharmacists in Academia 14

4 for weight uniformity as the weights of more than two tablets in these brands deviated from the mean value by an amount greater than 5.0 % (Table 1). This indicated that the tablets in each batch of these four brands will vary in weights outside the official limits. In the friability test, all the brands gave a weight loss of < 1% w/w, showing compliance with the BP (2007) specification (Table 1). Hence, all the brands could withstand abrasion without loss of tablet integrity. Table 1. Uniformity of weights and friability of ten brands of vitamin C tablets. Sample Friability(%) Weight (g) Uniformity (Mean ± SEM) T ±0.052 T ±0.086 T I±0.068 T ±0.046 T ±0.092 T ±0.057 T ±0.082 T ±0.079 T ±0.042 T ±0.071 T1 T 10 : Various brands of vitamin C tablets. Table 2. Disintegration and Dissolution rate profiles for ten brands of Vitamin C tablets. Sample Time (min) % Dissolution at 45 min Disintegration To attain 70% Dissolution T ± T ±0.42 NILL T ± T ± T ± T ± T ±0.54 NILL T ±0.38 NILL T ± T ± T 1 T 10 : Various brands of vitamin C tablets. Similarly, all the brands complied with the official specification of less than 15 min as disintegration time for uncoated tablets (Table 2) (BP, 2007). Ability of these brands to disintegrate within this time limit is a good indication that the tablets will disintegrate in the gastrointestinal tract and release their contents into the system. The B.P. specifies that not less than 70 % w/w labeled content should dissolve at 45 minutes (BP, 2007). The dissolution rate profile showed that brands T 2, T 7 and T 8 did The Official Publication of Nigerian Association of Pharmacists in Academia 15

5 not attain 70 % dissolution throughout the 1 h period of determination and consequently had the lowest (22 59 %) percent dissolution at 45 min of all the brands (Table 2). These brands may exhibit poor bioavailability profiles in vivo as well as poor clinical performances. Brand T 10 had the highest (98 %) dissolution while the remaining brands had % at 45 min (Table 2). The disintegration time and dissolution rates have direct bearing on the bioavailability profile of tablet dosage forms as it can be used to predict the drug release pattern in vivo (Olaniyi et al., 2001). Table 3. Ascobic acid content of ten brands of Vitamin C tablets Sample % w/w Ascorbic acid content: Titrimetric 1 * Titrimetric 2 Colorimetric T ± ± ±1.6 T ± ± ±2.5 T ± ± ±3.8 T ± ± ±3.5 T ± ± ±4.3 T ± ± ±3.2 T ± ± ±2.9 T ± ± ±4.6 T ± ± ±2.3 T ± ± ±2.9 * :Titrimetric method with 0.05 M Iodine solution; : method with 0.1 M Ammonium cerium(iv) sulphate. Table 4. Ascobic acid content of ten brands of Vitamin C syrups. Sample % w/w Ascorbic acid content: Titrimetric 1 * Titrimetric 2 Colorimetric S ± ± ±2.6 S ± ± ±3.2 S ± ± ±3.8 S ± ± ±2.5 S ± ± ±4.3 S ± ± ±4.1 S ± ± ±2.8 S ± ± ±3.4 S ± ± ±2.7 S ± ± ±2.2 * :Titrimetric method with 0.05 M Iodine solution; : method with 0.1 M Ammonium cerium(iv) sulphate. The results of the ascorbic acid assays using the two titrimetric and colorimetric methods for the powdered tablets were comparable (Table 3) and same for the assays of the syrups (Table 4). The The Official Publication of Nigerian Association of Pharmacists in Academia 16

6 results obtained for the assay were consistent for the two titrimetric and colorimetric methods for both the tablet and syrup formulations, indicating that any of the methods could be used, depending on the availability of the necessary materials. The excipients of the tablets did not interfere with the assay procedure and result, as the colour at the end point was clear and stable. Only 60 % of the tablet brands (T 1, T 2, T 4, T 7, T 9, T 10 ) and 40 % of the syrup brands (S 1, S 3, S 4, S 8 ) had their percentage ascorbic acid content within the % range specified in the BP (2007). Other samples had their values less than the B.P. specifications (Tables 3, 4). The brands T 2 and T 7 that had 98 and 103 % ascorbic acid contents, respectively using titrimetric 1 method did not achieve 70 % dissolution at 45 min, indicating a possible formulation problem. These brands, although contained the required amount of ascorbic acid, would not release the required amount in the body leading to therapeutic failure. Thus for a drug to produce the desired effect in the body, both the quality of the chemical content and the quality of formulation procedures are essentials. Sixty and forty percents of vitamin C tablet and syrup brands, respectively had ascorbic acids content within the pharmacopoeia limits, although some of these tablet brands failed the dissolution profile and weight uniformity tests, indicating that some of the brands are substandard with consequent therapeutic failure. In conclusion therefore, in ascertaining quality of the brands of drugs, assays for active constituents should be combined with assessment of other pharmaceutical characters. Acknowldegment The authors acknowledge Novel Pharmaceutical Industry, Lagos, Nigeria for the gift of pure Vitamin C powder. References Adegbolagun, O.A., Olalade, O.A., Osumah, S.E Comparative evaluation of the biopharmaceutical and chemical equivalence of some commercially available brands of ciprofloxacin hydrochloride tablets. Tropical journal of Pharmaceutical Research, 6(3): British Pharmacopoeia. Vol. 1 and The Pharmaceutical press. Her Majesty s Stationery Office, London. Lee, S.H., Oe, T., Blair, I.A Vitamin C- induced decomposition of lipid hydroperoxides to endogenous genotoxinns. Science, 292(5524) Levine, M., Wang, Y, Padayatty, S.J., Morrow, J A new recommended dietary allowance of Vitamin C for healthy young women. Proc Natl Acad Sci USA, 98: Odeniyi, M.A., Adegoke, O.A., Adereti, R.B., Odeku, O.A., Itiola, A.I Comparative analysis of eight brands of sulphadoxine-pyrimethamine tablets. Trop. J. Pharm. Research, 2(1): Olaniyi, A.A., Babalola, C.P., Oladeinde, F.O., Adegoke, A.O Eds. Towards better quality Assurance of Drugs : Proceedings of 4th National Workshop, Dept. Of Pharmaceutical Chemistry, University of Ibadan, Ibadan Padayatty, S.J., Katz, A. Wang, Y., Eck, P., Kwon, O., Lee, J.Y Vitamin C as an antioxidant: evaluation of its role in disease prevention. J Am Coll Nutr. 22: Remington s Pharmaceutical Sciences Mack Publishing Company. 18th Ed. World Health Organization, Fact Sheet No. 275, The Official Publication of Nigerian Association of Pharmacists in Academia 17