Formulation and Evaluation of Tramadol Hydrochloride Microspheres for Oral Delivery


Sanat Kumar Basu1, Kunchu Kavitha2* and Mani Rupeshkumar3

1Division of Pharmaceutics, Dept. of Pharmaceutical Technology, Jadavpur University, Kolkata - 700 032, India.           2Dept. of Pharmaceutics, Bharathi College of Pharmacy, Bharathi Nagara, Mandya Dist, Karnataka -571 422, India.             3Dept. of Pharmacology, Bharathi College of Pharmacy, Bharathi Nagara, Mandya Dist, Karnataka - 571 422, India.

*Corresponding Author E-mail:



Microspheres (MS) of Tramadol Hydrochloride (TM) were prepared by coacervation method without the use of chemical cross–linking agent (glutaraldehyde) to avoid the toxic reactions and other undesirable effects of the chemical cross-linking agent. Alternatively, ionotropic gelation was employed by using sodium-tripolyphosphate (Na-TPP) as cross linking agent. Chitosan was used as polymer. All the prepared microspheres were subjected to various physico-chemical studies, such as drug-polymer compatibility by thin layer chromatography (TLC) and Fourier Transform Infrared Spectroscopy (FTIR), surface morphology by scanning electron microscopy (SEM), frequency distribution, encapsulation efficiency by High Performance Thin Layer Chromatography (HPTLC), in-vitro drug release characteristics and release kinetics. TLC and FTIR studies indicated no drug-polymer incompatibility. Surface smoothness of MS was increased by increasing the polymer concentration, which was confirmed by SEM. As the drug to polymer ratio was increased, the mean particle size (MPS) of TM microspheres was also increased. A maximum of 87% of drug entrapment efficiency was obtained by the method employed. All the MS showed initial burst release followed by a Fickian diffusion mechanism. It is possible to design a controlled drug delivery system for the prolonged release of TM, improving therapy by possible reduction of time intervals between administrations.


KEYWORDS: Tramadol Hydrochloride; Microspheres; Coacervation; Chitosan; In-vitro release kinetics.



The present study reports a novel attempt to prepare coacervates of Chitosan as carrier for the widely used nonsteroidal anti inflammatory drug (NSAID) Tramadol Hydrochloride(TM). It is a centrally acting opioid analgesic, is used in severe acute or chronic pains. Tramadol is an aminocyclohexanol derivative or 4-phenyl piperidine analogue of codeine. Its analgesic effect is mediated through norepinephrine reuptake inhibition1. The mean elimination half-life is ~6 hours and requires dosing every 6 hours in order to maintain optimal relief of chronic pain2. Consequently, once-daily extended-release tablets have been formulated (tramadol ER). Long-term treatment with sustained-release tramadol once daily is generally safe in patients with osteoarthritis or refractory low back pain3 and is well tolerated. Tramadol offers several therapeutic advantages over other analgesics, such as good oral bioavailability and long elimination half-life (5–7 h). Despite the long elimination half-life, TM is prescribed 3–4 times a day.


Frequent dosing schedule often leads to decreased patient compliance, increased incidence of side effects and tolerance development, especially, in long-term use in conditions like arthritis, osteoarthritis, arthralgia, postoperative surgical pains, etc. It seems that there is a strong clinical need and market potential for a delivery system that can deliver TM in a controlled manner4, 5. TM’s apparently negligible effect on respiration, as demonstrated in studies in adults and children, suggests that tramadol may offer a distinct advantage over typical opioid analgesics for the relief of postoperative pain in children6. To reduce the frequency of administration and to improve patient compliance, a sustained-release formulation of Tramadol is desirable.


Chitosan or β(1, 4) 2-amino-2-deoxy-D-glucose is a hydrophilic biopolymer obtained by hydrolysis of the amino acetyl groups of chitin, a polysaccharide found in a wide variety of crustaceans, insects and fungi. Chitosan with excellent biodegradable and biocompatible characteristics is a naturally occurring polysaccharide. Chitosan has been extensively used by many researchers for the encapsulation and controlled delivery of various drugs7-9.

Recently reversible physical cross-linking by electrostatic interaction, instead of chemical cross-linking is applied to avoid possible toxicity of reagents and other undesirable effects. Na-TPP is a poly anion, and can interact with cationic Chitosan by electrostatic forces10,11. Hence, microspheres of TM for oral delivery were developed with the aim to improve patient compliance and to obtain improved therapeutic efficacy in the treatment of post operative pain and migraine.



2.1. Materials:

Tramadol Hydrochloride was obtained from (Sun Pharmaceutical Industries Ltd., Maharashtra, India) as a gift sample, Chitosan with a degree of deacetylation of > 85% and viscosity of  500cps at 1%(w/v) in 1 % (v/v) aqueous acetic acid at 200C was supplied from (Central Institute of Fisheries and Technology, Cochin, India) as a gift sample and was used as received. Sodium tri polyphosphate (Na-TPP) from (Fluka Chemical Company, GmbH, Switzerland), light and heavy liquid paraffins, tween 80, acetone, glacial acetic acid, methanol and other chemicals were from India (S.D. Fine Chem. Limited, Mumbai, India).


2.2. Preparation of tramadol hydrochloride microspheres:

The TM microspheres were prepared by simple coacervation technique by using Chitosan as coating material. Chitosan was dissolved in dilute acetic acid solution (1% v/v) at concentrations of 1-4% w/v and adjusted to a certain solution pH (usually 5.0). TM (100mg) was dissolved in the above polymeric solution. The drug in polymeric solution was emulsified in 200ml of liquid paraffin (1:1 mixture of light and heavy liquid paraffin) containing 1ml tween 80 (2% w/v). The emulsification time was allowed for 10min under mechanical stirring (500 rpm). Then 50ml   Na-TPP (1%w/v) with pH in the range 4-5 was added drop wise. Stirring was continued for 15-60min to obtain cross-linked microspheres. Microspheres were collected by centrifugation and washed with double distilled water several times, then with acetone to remove water and dried at room temperature under vacuum. The prepared microspheres were stored in desiccator for further studies. TM loaded microspheres with different polymer compositions (1:1, 1:2, 1:3 and 1:4) were named asTS1, TS2, TS3 and TS4 respectively.


2.3. Compatibility studies:

Chemical interaction between the drug and the polymeric material, if any, during the preparation of the microspheres was studied by using Thin Layer Chromatography (TLC) and Fourier Transform Infrared Spectroscopy (FTIR).


2.3.1. Thin Layer Chromatography (TLC):

Thin Layer Chromatography was carried out in TLC chamber. The sample solutions of pure drug and prepared microspheres were prepared by dissolving in methanol and applied to silica gel G plates. The plates were then developed in the following solvents systems.

Solvent system 1:  Chloroform: methanol: Acetic acid 9:2:0.1 (% v/v/v)

Solvent system 2: Chloroform: Toluene: Ethanol 9:8:1 (% v/v/v).


The Rf value of the pure drug as well as prepared microspheres were determined by placing the plates in an iodine chamber and the Rf value of pure drug was compared with the Rf value of prepared microspheres.


2.3.2. Fourier Transform Infrared Spectroscopy (FTIR):

Infrared (FTIR) spectrum of the drug, drug loaded microspheres, blank microspheres and physical mixture of drug and empty microspheres were recorded using a FTIR (model 4100 type A, Perkin-Elmer, Norwak, CT, USA) spectrometer using KBr pellets (400-4000-1) with a scanning speed of 2 mm/sec with normal slit.


2.4. Scanning Electron Microscopy (SEM):

The shape and surface morphology of the TM loaded microspheres were studied using (Jeol, JSM-840A scanning electron microscope, Japan). The gold coated (thickness 200A0; Jeol, JFC-1100E sputter coater, Japan) microspheres were subjected to secondary imaging technique at 150 tilt, 15mm working distance and 20Kv accelerating voltage.


2.5. Frequency distribution analysis:

Samples of microspheres were analyzed for frequency distribution with calibrated optical microscope fitted with a stage and an ocular micrometer. Small quantities of MS were spread on a clean glass slide and the average size of 200 particles and frequency distribution were determined in each batch using the calibration factor.


2.6. Determination of Percentage Drug Entrapment (PDE):

Efficiency of drug entrapment for each batch was calculated in terms of percentage drug entrapment (PDE) as per the following formula;



2.6.1. Theoretical drug loading:

Theoretical drug loading was determined by calculation assuming that the entire drug present in the polymer solution used gets entrapped in microspheres, and no loss occurs at any stage of preparation of microspheres12.


2.6.2. Practical drug loading:

Practical drug loading was analyzed as follows. 20mg of microspheres were added to100ml of glacial acetic acid (1%v/v) and methanol in the ratio of 3:2 and occasionally shaken for 30min. The solution was centrifuged and 1ml of the clear supernatant was diluted to 10ml with 0.1N HCl, the supernatant liquid was filtered through Watt Mann filter paper and analyzed for TM by High Performance Thin Layer Chromatography (HPTLC) as described below13.

The quantitative determination of TM in microspheres was carried out by using a Camag HPTLC system with Win CATS 4 software, Linomat 5 sample applicator and scanner was used for the analysis and interpretation of data. The experiment was performed on a silica gel G60 F254. HPTLC plates (20*10) using mobile phase comprised of Chloroform: methanol: Acetic acid 9:2:0.1 (% v/v/v).The plates were activated by at 1100 for 30 min prior to chromatography. Samples were applied as 6mm bands at 10mm interval under a stream of inert gas. Ascending development to distance of 76mm was performed in saturated 20*10 twin trough TLC developing chamber for 30min at room temperature. The plate was scanned and quantified at 270nm using slit dimension of 5*0.45mm at a scanning speed of 20mm/s. The peak area was noted after development and the amount present in microspheres was calculated using respective standard calibration curve.


2.7. In- vitro drug release studies:

Microspheres equivalent to 200mg TM were subjected to in-vitro drug release studies in simulated gastric fluid (pH 1.2 buffer) from 0-2h, simulated intestinal fluid (pH 7.4 phosphate buffer) from 2-12h to assess their ability in providing the desired controlled drug delivery.  Drug release studies were carried out using USP XXIII basket dissolution rate test apparatus (100 rpm, 37 ± 10C). At different time intervals, 5ml of the sample was withdrawn and replaced with same amount of fresh medium. The sample was analyzed for TM at 271nm using a UV/ VIS spectrometer against a reagent blank. The in-vitro release pattern of the selected best batch (TS3) of TM microspheres was compared with the marketed SR product.


2.8. Kinetics of drug release:

To examine the drug release kinetics and mechanism, the cumulative release data were fitted to models representing zero-order (Q v/s t), first-order (log (Q0-Q) v/s t), Higuchi’s square root of time (Q v/s t1/2) and Korsemeyer peppas double log plot (log Q v/s log t) respectively, where Q is the cumulative percentage of drug released at time t and (Q0-Q) is the cumulative percentage of drug remaining after time t. The release kinetics of selected best batch (TS3) was compared with the marketed SR product.



3.1. Formulation optimization of Tramadol hydrochloride microspheres:

The formulation conditions for the preparation of coacervates were first optimized It can be seen that the solution pH may play an important role on the chitosan microsphere formation. Complex coacervation is a pH-sensitive process since the charge and charge density of the polymers vary with pH. Chitosan is always positively charged in solution while the charge of the gelatin molecules depends on the pH. Coacervation between chitosan and gelatin should be restricted to a narrow pH range, where both molecules carry opposite charges. The investigated pH range was 4.5 to 6.5, which is above the isoelectric point of gelatin and below the pH of precipitation of chitosan. The coacervate yield dropped at pH values below and above this pH. Above pH 6.25 chitosan precipitated from solution. The pH of maximum coacervate yield is believed to correspond to the electrical equivalence of pH (EEP), where both polymers carry equal but opposite charges. At EEP, attracting forces between the charged components neutralize each other leading to strong binding and the highest coacervate yield. At pH values where the charges are no longer balanced, a reduction in the interaction between the polymers causes a reduction in the coacervate yield.  In this study the pH of polymer solutions and the cross-linker solutions were usually adjusted to 4-5. This is valuable for the selection of the preparation conditions of ionotropic gelation of chitosan microspheres14, 15.


3.2. Compatibility studies:

Chemical interaction between drug and the polymeric material, if any, during the preparation of the microspheres was studied by using a TLC and FTIR. The comparable Rf values of pure drug and microencapsulated drug in the TLC study indicated the compatibility of drug with polymer and other excipients used in the preparation of TM microspheres16. No difference in the IR patterns of a physical mixture of the drug and blank microspheres, and drug loaded microspheres was observed (Fig. 1). Therefore, the FTIR studies ruled out the possibility of any drug polymer interaction during the preparation of microspheres17.


Fig. 1.  Fourier Transform Infrared (FTIR) Spectrum

a. Tramadol Hydrochloride drug

b. Tramadol Hydrochloride loaded microspheres

c. Physical mixture of Tramadol Hydrochloride and blank microspheres

d. Blank microspheres.


3.3. Morphological characteristics (SEM):

The surface morphology of the TM and TM loaded microspheres were studied by scanning electron microscopy (Fig. 2). Surface smoothness of microspheres was increased by increasing the polymer concentration, which was confirmed by SEM. At lower polymer concentration (1% w/v) rough and wrinkled surface of microspheres was obtained (Fig. 2a) and at higher polymer concentration (4%) the microspheres with smooth surface was obtained (Fig. 2b).


Fig. 2. Scanning Electron Micrographs (SEM) of Tramadol Hydrochloride Microspheres.

a. Microspheres prepared with 1:1 drug/polymer ratio

b. Microspheres prepared with 1:4 drug/polymer ratio


Fig. 3. Frequency distribution of Tramadol Hydrochloride microspheres.


3.4. Particle size distribution:

The results of accuracy and precision of frequency distribution studies and histograms showed the normal frequency distribution of microspheres (Fig. 3). As the drug to polymer ratio was increased, the mean particle size (MPS) of TM microspheres was also increased (Table 1). The significant increase may be because of the increase in the viscosity of the droplets (due to the increase in concentration of polymer solution). This increase is high enough to result in difficult dispersion and subdivision of droplets reported18, 19. A surfactant (tween 80) was found to play an important role in controlling the particle size of the micro coacervates. As the tween concentration increased from 0.5-2.0% w/v the particle size reduced. However, further increase in the tween concentration produced bigger particles. The presence of tween 80 was found to be essential for reducing aggregation of the microspheres.


Table 1. Particle size, Drug entrapment and encapsulation efficiency of TM microspheres


Mean particle size

(µm) ± SEM

(%)Drug entrapment

Drug Encapsulation Efficiency (%)


259.35 ± 8.21




342.90 ± 9.84




390.75 ± 10.88




481.95 ± 11.70




3.5. Drug entrapment efficiency:

The drug loading efficiency of TM microspheres was determined by HPTLC method. A maximum of 87% of drug entrapment efficiency was obtained by the method employed. By increasing the polymer concentration the encapsulation efficiency was increased (Table 1).


3.6. In-vitro drug release studies:

The in-vitro release of Tramadol Hydrochloride microspheres were studied in the pH 7.4 phosphate buffer medium. It is reasonable to conclude that the release profiles of TM from the microspheres showed two distinct phases. An initial burst release phase occurs in the first hour, followed by a gradual release phase. It was observed that the rate of release decreased as the concentration of the carrier was increased. This may be due to low permeability of polymer to the drug. The in-vitro release profiles are shown in Fig. 4. The in-vitro release pattern of the selected best batch (TS3) of TM microspheres was compared with the marketed SR product shown in (Fig. 5).Comparison of release pattern of batch TS3 with marketed SR product, showed the similar release pattern of marketed SR product. All the parameters were run 3 times (n=3). The difference in mean of drug release of batch series ‘TS’ was significant (p < 0.05).


Fig. 4. In - vitro release of Tramadol Hydrochloride microspheres.


Table 2. Diffusion exponent (n) of Peppas model and Regression co-efficient (r2) of TM release   data from microspheres according to different kinetic models.


Peppas Model (n)

Zero order

First order




0.983 ± 0.004

0.917 ± 0.003

0.942 ± 0.005



0.975 ± 0.003

0.890 ± 0.002

0.928 ± 0.006



0.985 ± 0.004

0.952 ± 0.004

0.938 ± 0.004



0.989 ± 0.005

0.988 ± 0.004

0.970 ± 0.002

SD=Standard deviation (n=3) the difference in mean of %Cumulative Release, Zero order, First order, Higuchi kinetics, Peppas Equation between batch series ‘TS’ was significant (p < 0.05).



Fig.5.Comparision of In vitro release of best batch TS3 and marketed SR product (MKT).


3.7. Release kinetics:

The data obtained in In-vitro release study were fitted to zero order, first order, Higuchi square root of time and Korsemeyer-Peppas equations to understand the mechanism of drug release from the microspheres20. The slopes and the regression co-efficient of determinations (r2) are listed in Table 2. The co-efficient of determination indicated that the release data was best fitted with zero order kinetics. Higuchi equation explains the diffusion controlled release mechanism. Additional evidence for the diffusion controlled mechanism was obtained by fitting the Korsmeyer-Peppas equation to the release data. The diffusion exponent ‘n’ value was found to be less than 0.5 for different drug polymer compositions, indicating Fickian diffusion of drug through microspheres. Thus all microspheres showed initial burst release followed by Fickian diffusion. The release kinetics of the selected best batch (TS3) was compared with the marketed SR product. The marketed product showed the zero order release kinetics (r2=0.9978) followed by Fickian diffusion (n=0.3364).



The micro particulate drug delivery system proposed in this work based on Chitosan, a natural biodegradable polymer, seems to hold promise for oral administration of Tramadol Hydrochloride. The method of preparation of Chitosan microspheres of TM was found to be simple and reproducible. Chitosan, which is used as a carrier, is easily available and biocompatible. From the above data, it may be concluded that drug loaded microspheres are a suitable delivery system for TM and may help to reduce the dose of the drug and frequency of administration.


The authors are thankful to Sun Pharmaceutical Industries Ltd., Maharashtra, India for gift sample of Tramadol Hydrochloride, Central Institute of Fisheries and Technology, Cochin, India for providing gift sample of Chitosan, respectively. The authors greatly acknowledge Indian Institute of Science (IISC), Bangalore, India for the technical assistance in analytical studies.



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Received on 27.02.2010       Modified on 19.03.2010

Accepted on 07.04.2010      © RJPT All right reserved

Research J. Pharm. and Tech.3 (3): July-Sept. 2010; Page 877-881