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Year : 2011  |  Volume : 2  |  Issue : 1  |  Page : 14-19  

Negative intercepts in the Heckel analysis of the crude extract of Vernonia galamensis: A major setback of the equation

Department of Pharmaceutics and Pharmaceutical Microbiology, Faculty of Pharmaceutical Sciences, Ahmadu Bello University, Zaria, Nigeria

Date of Web Publication15-Jul-2011

Correspondence Address:
Musa Autamashih
Department of Pharmaceutics and Pharmaceutical Microbiology, Faculty of Pharmaceutical Sciences, Ahmadu Bello University, Zaria
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0976-9234.82987

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Introduction: The dry powdered leaf of Vernonia galamensis (Asteraceae) has been used by traditional herbalists in northern Nigeria to treat diabetes mellitus. However, medicinal plants used in folk medicine have no standard dose or acceptable method of formulation. In this study therefore, the leaves of Vernonia galamensis (Asteraceae) were extracted, evaluated for pharmacological activity and formulated into tablets. Materials and Methods: The extract was found to be highly hygroscopic and deliquescent, therefore the following efflorescent diluents; aerosil® 200 (GmbH, Meggle, Germany), avicel PH 101 (Honey Well and Stein, UK), and anhydrous calcium phosphate (BDH chemicals, England) were used. The wet granulation method was employed for the tablet formulation and the compaction characteristics of the granules were determined using the Heckel equation. Results and Conclusions: Negative intercepts were a setback to the use of the Heckel equation due to the resulting negative values of D A and D B . This makes it difficult to explain the compaction characteristics of the crude extract.

Keywords: Compaction characteristics, diabetes, medicinal plants, tablets

How to cite this article:
Autamashih M, Isah AB, Allagh TS. Negative intercepts in the Heckel analysis of the crude extract of Vernonia galamensis: A major setback of the equation. J Pharm Negative Results 2011;2:14-9

How to cite this URL:
Autamashih M, Isah AB, Allagh TS. Negative intercepts in the Heckel analysis of the crude extract of Vernonia galamensis: A major setback of the equation. J Pharm Negative Results [serial online] 2011 [cited 2020 Jul 14];2:14-9. Available from:

   Introduction Top

Medicinal plants have been successfully used for centuries by man as remedies in the treatment of ailments. However, the advent of chemotherapeutic agents and synthetic drugs led to decline popularity of the herbal medicines. Recently however, there have been renewed interests in herbal medicines all over the world because of the severe side effects of many of the potent chemicals. [1],[2]

The decoction of the leaf of Vernonia galamensis (Asteraceae) has been used by traditional herbalists for ages in the treatment of diabetes mellitus. This information was revealed through oral communication with some traditional healers in northern Nigeria on an effort towards identifying active medicinal plants for the treatment of diseased conditions. However, medicinal plants used in folk medicine generally have no standard dose or acceptable method of formulation. [3] Efforts have therefore been made by some pharmaceutical formulators to formulate active medicinal plant parts into suitable dosage forms. In few cases the activity of the crude plant extract is provided by a single component, in such cases the component is isolated and characterized before formulation. But in many cases the activity is provided by a combination of many components such that separating them always leads to loss of activity. In such situations, the crude extract is formulated as such without isolation. Of recent, some scientists have formulated tablets from plant crude extracts without isolation and have used the Heckel relation for predicting the powder characteristics of the extracts. [4],[5],[6] In this study, attempts are made to extract, quantify and formulate the leaf of Vernonia galamensis (EVG) into tablets and to investigate the compaction characteristics using the Heckel equation. The tablet dosage form was selected because tablets are the most frequently used dosage form and have advantages for both manufacturer and user. Durability, ease of administration, convenience of administration and accurate dosing make tablets a versatile and popular dosage form. [7]

The Heckel equation has been by far the most popular in recent years among pharmaceutical scientists, [8] and many apparent yield pressure values ('in-die", P y) and mean yield pressure values ('out-of-die') of active substances and tableting excipients have been published. The model has often been applied to study powder mixtures and to evaluate granule manufacture of crude plant extracts. [7]

   Materials and Methods Top


Vernonia galamensis (Astereceae) leaves (obtained from the natural habitat of Ahmadu Bello University, Zaria, Nigeria), Swiss albino rats 150-229 g (maintained at the animal house of the Department of Pharmacology and Clinical Pharmacy of the University), polyvinylpyrrolidone, maize starch, gelatin (May and Baker, Germany), aerosil® 200 (GmbH, Meggle, Germany) and Avicel® PH 101 (Honey Well and Stein Ltd, UK). All other chemicals and reagents used were of analytical grade


Preparation of the extract

Leaves of Vernonia galamensis were plugged from the stem, washed with distilled water, dried in open air and milled to a coarse (1000 μm) powder. The powder was then soaked in distilled water for 24 h at room temperature and the liquid extract filtered through a calico cloth and concentrated to a ratio of 5:1 using a rotary evaporator. The concentrated filtrate was then dried at 60°C, pulverized and passed through a 150 μm sieve.

Phytochemical screening of the dried extract

Phytochemical tests such as test for the absence or presence of saponins, glycosides, alkaloids and tannins were carried out on the dried aqueous extract obtained according to the methods adopted by Trease and Evans (1989). [9]

Evaluation of hypoglycemic activity on alloxan-induced diabetic rats

Diabetes was induced in male albino rats weighing about 180-220 g by intraperitoneal administration of 150 mg/kg body weight aqueous alloxan monohydrate and the animals monitored for 72 h. Alloxan-treated rats with fasting blood glucose levels ≥200mg/dl were considered hyperglycemic. [10] Samples of extracts were administered orally to each of four groups of male albino rats at stepping up doses (200, 500, 750 and 1000 mg/kg) at suitable time intervals (0, 1, 3, 5, and 7 h). The fifth group served as control and was administered normal saline (sodium chloride 0.9%w/v). Metformin 28.6 mg/kg (2000 mg/70 kg), per oral was used as the standard antidiabetic agent for comparison. Blood samples were squeezed out from the tale (after a slight cut) into a Glucometer (One Touch Basic; LifeScan, Johnson and Johnson Company Inc., California, USA) with the test strip and the reading taken at time zero, and the process repeated three times. All procedures involving use of the animals were approved by the ethical committee of the Faculty of Pharmaceutical Sciences of the institution.

Acute toxicity studies to determine the lethal dose (LD 50 ) of extract

Adopting the method of Lorke (1983), [11] the oral (p.o.) route was used (since we are working with crude rather than pure compound) for the determination of the acute toxicity (LD 50 ) of the extract. Forty rats divided into eight groups of five were used for assessing the LD50. Varying doses of the extract (500, 1000, 1500, 2000, 5000 mg/kg body) were given to the animals as single doses and a control group received normal saline solution. All animals were observed for mortality over 24 h.

Separation of crude extract components by stepwise fractionation procedure

Five gram of the powdered leaf was weighed into a 250 ml stoppered conical flask and 100 ml petroleum ether was added and shaken in a mechanical shaker for 6 h and allowed to stand for 18 h. The mixture partitioned into the organic portion known as the petroleum ether portion at the top of the flask and the aqueous fraction known as fraction 1 (F 1 ) at the bottom. The petroleum ether portion was evaporated to dryness and kept for test of antidiabetic activity whereas F 1 was used for step II where ethanol was added to it and subsequent fractionation and partitioning continued as shown in [Table 1].
Table 1: Stepwise fractionation procedure

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All the various solvent extracts obtained from the fractionation were evaporated to dryness and their antidiabetic properties determined on alloxan-induced diabetic rats.

Formulation studies

Preparation of binders

Maize starch (MS) powder required to make 5.0% w/v was suspended in a little quantity of cold water to form a smooth suspension (free from chumps). Boiling water was then added to the suspension up to the 100th cm 3 mark and stirred until mucilage is formed. The mucilage was then allowed to cool to about 40°C before it was incorporated as a binder. Polyvinylpyrrolidone (PVP) powder required to make 5.0% w/v in cold water was stirred until all the powder went into solution. Gelatin (GLT) powder required to make 5% w/v in cold water was allowed to hydrate and the suspension warmed on a water bath until a flowable material was obtained. To avoid gelling, the powder was kept warmed (about 40°C) during use.

Tablet formula

The tablet formula was designed by varying the type and quantities of the diluents, disintegrants and binders

[Table 2] to obtain tablets of highest quality.
Table 2: Tablet formula for respective batches

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Preparation of granules

These were done according to the methods adopted by Isimi et al, 2003. [5]

Preparation and analysis of compacts

Compacts equivalent to 300 mg of granules were produced by compressing the granules for 60 s at various compression pressures using a single punch tablet machine (Tianxiang and Chentai Pharmaceutical Machinery Co. Ltd., Shanghai, China) fitted with 10.5 mm flat punch and die set. After ejection, the tablets were stored over silica gel in a desiccator for 24 hour to allow for elastic recovery and hardening preventing false low yield values. Dimensions of the compacts were determined to the nearest 0.01 mm with a Mitutoyo model IDC-1012 EB micrometer gauge (Mitutoyo Corporation, Japan).

Heckel analysis: The Heckel equation is written as follows: [12]

where D is the ratio of the density of the powder mass at pressure P to the density of the powder mixture (i.e., relative density). K, the slope of the straight portion of the graph, reflects the reduction in porosity or the resistance to volume reduction of granules and A is a constant. The yield pressure, P Y, is usually calculated as the reciprocal of the linear portion of the slope of the Heckel plot. The relative density D A is calculated from the intercept, A, using the equation.

D B, the relative density during the rearrangement phase is calculated from the difference between D A and D O (relative density of the granules at nil pressure).

The non-linear regression of the XY analyses in the GraphPad Prism® version 5.03 software was used for statistical analysis and results were expressed as mean ± SD of at least three runs.

   Results and Discussion Top

Phytochemical analysis

Phytochemical studies show that the aqueous extract of Vernonia galamensis contains saponins, glycosides, carbohydrates, flavonoids and alkaloids.

Toxicity studies (Determination of LD 50 )

As much as 5000 mg/kg body weight of extract was administered orally to the animals and there was no record of any toxic effects within 24 h. LD 50 's >5000mg/kg body weight are of no practical interest, therefore the crude extract is relatively safe. [11]

Determination of minimal effective dose extract

[Table 3] presents the effects of increasing doses of the aqueous extracts (200, 500, 700 and 1000 mg/kg body weight, respectively) and that of the standard maximum dose of metformin on alloxan-induced diabetic rats (the standard maximum single dose of metformin for a 70 kg adult is 2000 mg i.e. 2000 mg/70 kg = 28.6 mg/kg). A dose of 700 mg/kg of the crude extract was observed to cause the maximum reduction in blood glucose level of 82.7%, which was found to be even more favorable to that of metformin (73.6%).
Table 3: Effects of different doses of crude aqueous extract of V. galamensis leaves and metformin on blood glucose level of alloxan-induced diabetic rats

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Hypoglycemic activity of components obtained from fractionation procedure

[Table 4] presents the effects of different solvents extracts (obtained from the stepwise fractionation) on the alloxan-induced diabetic rats. Batch I is the negative control and is normal saline (sodium chloride 0.9%w/v), batch II is the positive control and is the crude aqueous extract (700 mg/kg) and batches III to VII are the extracts of ethanol, pet ether, diethyl ether, ethyl acetate and n-butanol (700 mg/kg), respectively.
Table 4: Effects of different fractions of V. galamensis leaves extract obtained from fractionation procedure compared with that of the whole crude extract on diabetic rats

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Based on the Heckel's equation, three types of powder compression behavior have been identified, namely type A, B and C. [13] [Figure 1], [Figure 2] and [Figure 3] depict the Heckel plots for granules of crude extract of Vernonia galamensis (EVG) prepared using selected efflorescent diluents (due to the deliquescent property of the extract); aerosil® 200 (AR), Avicel® PH 101 (AV) and calcium phosphate (CP), and selected binders; maize starch (MS), polyvinylpyrrolidone (PVP) and gelatin (GLT). Near parallel relationships were observed with the plots at all applied pressures and they are more indicative of type-A materials. This implies that the granules containing these combinations at all concentrations of the PVP principally undergo plastic deformation. [14]
Figure 1: Heckel plots for Extract of Vernonia galamensis (EVG)/Selected diluent [aerosil (AR), avicel (AV) or calcium phosphate (CP)/Maize starch (MS) compacts at column width

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Figure 2: Heckel plots for Extract of Vernonia galamensis (EVG)/Selected diluent [aerosil (AR), avicel (AV) or calcium phosphate (CP)/Polyvinylpyrrolidone (PVP) compacts at column width

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Figure 3: Heckel plots for Extract of Vernonia galamensis (EVG)/Selected diluent [aerosil (AR), avicel (AV) or calcium phosphate (CP)/Gelatin (GLT) compacts at column width

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P y which is the yield pressure is an important indication of granule compressibility and it describes the tendency of the material to deform either by plastic flow or fragmentation. A faster degree of plastic deformation is reflected by a low P y value (steep slope) in a general sense. A low P y value, however, need not necessarily reflect that the compact has an acceptable tensile strength. [15] [Table 5] shows that for all binders used (MS, PVP and GLT), formulations made with CP as diluent gave lowest P y values indicating that granules prepared with CP deformed plastically at lowest pressures compared to those of AV and AR.
Table 5: Intercepts and Heckel constants for different tablet formulations of V. galamensis crude extract

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From the different formulations using the selected efflorescent diluents with the different combinations of binders, negative intercepts were observed in all cases. This negative values of intercepts may be due to the intrinsic characteristics of the extract; being deliquescent in nature. The negative intercepts gave rise to negative values of both D A and D B by calculation. Given some more thoughts to this, D A represents the total degree of densification at zero and low pressures and D B represents the particle rearrangement phase in the early compression stages, which also indicate the extent of granule fragmentation. [16] This means that for any situation where zero values of D A and D B are obtained, it would mean that there is no densification at zero and low pressure and no particle rearrangement phase or granule fragmentation at all. However in this situation where negative values (less than zero values) of the D A and D B were obtained, it is impracticable to explain the degree of densification at zero and low pressures and the particle rearrangement phase or the extent of granule fragmentation by the use of the Heckel equation. Certainly, this is another limitation of the equation. Few researchers have also noticed negative intercepts while using the Heckel equation to investigate the compaction characteristics of their powders or granules, [9],[17],[18] but none have explained the implication of having the resulting negative values of D A and D B which is the inability to explain the degree of densification at zero and low pressures, and the particle rearrangement phase or the extent of granule fragmentation.

   Conclusion Top

While applying the Heckel analysis to investigate the compaction characteristics of the dry deliquescent crude extract of Vernonia galamensis, negative intercepts were observed in all the different formulations. This uncovers a major limitation to the use of the equation due to the resulting negative values of D A and D B , and makes it impossible to explain the degree of densification at zero and low pressures, the particle rearrangement phase and extent of granule fragmentation. Other equations like those of the Kawakita and Walker are therefore recommended for adequate investigation of the compaction characteristics of this crude extract as well as all other powders having similar characteristics.

   References Top

1.Dans AM, Villarruz MV, Jimeno CA. The effect of Momordica charantia capsule prepared on glycerin control in type 2 diabetes mellitus needs further studies. J Clin Epideminol 2007;60:554-9.  Back to cited text no. 1
2.Gratus C, Wilson S, Greenfield SM, Damery SL, Warmington SA, Grieve R, et al. The use of Herbal medicines by people with cancer: A quantitative study. Complement Altern Med 2009;14:9-14.  Back to cited text no. 2
3.Allagh TS, Ameh GO, Okafor IS. Formulation and evaluation of the physicochemical properties of Ageratum Conyzoides (Fam asteraceae) granules and tablets. Niger J Pharm Sci 2009;8:18-25.  Back to cited text no. 3
4.Kunle OO, Nasipuri RN, Oyewumi MO, Ojile JE Wambebe CN. Formulation studies on the hot water leaf extract of Ficus sur (Moraceae): Compaction characteristics and effect of magnesium stearate on granule and tablet properties. Acta Pharm 1999;49 : 189-99.  Back to cited text no. 4
5.Ismi CY, Nasipuri RN, Ojile JB, Ibrahim YK, Emeje M. Effects of the diluent type on compressional characteristics of the mixed stem bark extract of Anogeissusleiocarpus and Prosopis Africana tablet formulation. Acta Pharm 2003;53:49-56.  Back to cited text no. 5
6.Luiz A, George G, Pedro P, Peter C. Dry Granulation and Compression of Spray-Dried Plant Extracts. AAPS Pharm Sci Tech 2005;6:45-50.  Back to cited text no. 6
7.Ilija I, Kasa P, Dreu R, Pintye-Hodi K, Sircic S. The compressibility and compactibility of different types of lactose. Drud Dev Ind Pharm 2009;35:1271-80.  Back to cited text no. 7
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9.Trease GE, Evans WC. Pharmacognovsy. London: Bailliere tindall; 1989. p. 236-68.  Back to cited text no. 9
10.Ojewole JO. Hypoglycemic effect of Sclerocarya birrea (Anacardiaceae) stem-bark aqueous extract in rats. Phytomedicine 2003;10:675-81  Back to cited text no. 10
11.Lorke DA. New approach to practical acute toxicity testing. Arch Toxicol 1982;51:275-87  Back to cited text no. 11
12.Heckel RW. An analysis of powder compaction phenomena. Trans Metall Soc AIME 1961;222:1001-8.  Back to cited text no. 12
13.Hersey JA, Rees JE. Deformation of Particles During Briquetting, in Proceedings of the 2 nd Particle Size Analysis Conference. Bradford: Society for Analytical Chemistry; 1970. p. 33.  Back to cited text no. 13
14.York P, Pilpel N. The tensile strength and compression behavior of lactose, four fatty acids and their mixtures in relation to tableting. J Pharm Pharmacol 1973;25:1-11.  Back to cited text no. 14
15.Hyunjo K, Gopi V, Fassihi R. Compatibility characterization of granular fraction for Tableting using a compaction simulator. Int J Pharm 1998;161:149-59.  Back to cited text no. 15
16.Emeje M, Isimi C, Kunle O. Effect of Grewia gum on the mechanical properties of paracetamol tablet formulations. Afr J Pharm Pharmacol 2008;2:2001-6.  Back to cited text no. 16
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18.Gonul N, Ogan-Hascicek C, Baykara T. The consolidation and compressibility proiperties of some novel directly compressible filler-binders. Acta Pol Pharm 2000;57:311-7.  Back to cited text no. 18


  [Figure 1], [Figure 2], [Figure 3]

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5]

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