INTRODUCTION:

1. Floating drug delivery systems:

FDDS have a bulk density lower that gastric fluid and thus remains buoyant in stomach for prolonged period of time without affecting gastric emptying time². They are also referred to as hydro dynamically balanced systems (HBS) as they are able to maintain their low density.¹

Based on mechanisms of floating, two different technologies i.e.

1. Effervescent FDDS

2. Non-effervescent FDDS

1) Effervescent systems:

When they reach the stomach CO₂ is liberated by the acidity of gastric content. When the liberated gas is expelled from the dosage form it creates pores through which water can easily pass and helps in wetting of the polymers. The CO2 generated compounds like sodium bicarbonate, calcium carbonate, citric acid, tartaric acid mixtures can be used⁴.

2) Non-effervescent systems:

Floating dosage forms use a gel forming or swellable cellulose type of hydrocolloids, polysaccharides and matrix forming polymers like polycarbonate, polyacrylate, polymethacrylate, and polystyrene⁴.

Received on 30.11.2014 Modified on 11.12.2014

Research J. Pharm. and Tech. 8(2): Feb. 2015; Page 145-153

DOI: 10.5958/0974-360X.2015.00025.6

After oral administration this dosage form swells in contact with gastric fluids and attains a bulk density of less than 1. The air entrapped within the swollen matrix imparts buoyancy to the dosage form. Losartan is a angiotensin inhibitor used in the treatment of hypertension. It has an oral bioavailability of less than 22%. It also undergoes high first pass metabolism³. It is highly soluble in acidic pH and absorbed more in the upper part of the GIT12. In order to improve the absorption and its oral bioavailability, we have attempted to formulate a floating drug delivery systems using Losartan as the model drug with HPMC K4M and Ethyl cellulose as polymers.

Floating systems or dynamically controlled systems are low density systems that have sufficiently buoyancy to float over the gastric contents and remain buoyant in the stomach without affecting the gastric emptying rate for a prolonged period of time². This results in an increased gastric retention time and a better control of the fluctuations in plasma drug concentration⁵. Many buoyant systems have been developed based on granules, powders, capsules, tab-lets, laminated films and hallow Microspheres.

Oral administration is the most convenient and preferred means of any drug delivery to the systematic circulation. The transit of a drug (formulation) through the gastrointestinal (GI) tract will determine how long a compound will be in contact with its preferred absorptive site. In humans, the small intestine transit time is reasonably constant: at around three hours for a drug formulation (or a meal) to pass from the stomach to the ileo-caecal junction¹⁰. Transit through the colon is much longer and can be 20 hours or more. Hence, the time a drug will have in its absorption window can be relatively short, so the drug is preferentially absorbed in the proximal small intestine (e.g. jejunum) rather than the small bowel. Even, the bioavailability of a drug, which is largely or exclusively absorbed from the upper GI tract, will be affected by factors that change GI tract¹⁰. Rapid gastrointestinal transit could result in incomplete drug release from the device above the absorption zone leading to diminished efficacy of the administered dose.

Gastro-retentive systems:

These systems can remain in the gastric region for several hours and hence significantly prolong the overall gastrointestinal transit time of drugs. Prolonged gastric retention improves bioavailability, reduces drug waste, and improves solubility for drugs that are less soluble in a high pH environment. It has applications also for local drug delivery to the stomach and proximal small intestines⁸. Gastro retention helps to provide, better availability of new products with new therapeutic possibilities and substantial benefits for patients. Therefore, different approaches have been proposed to retain the dosage form in the stomach including bio adhesive systems, swelling and expanding systems floating systems and delayed gastric emptying devices.

Present study demonstrates the formulation of sustained release floating matrix tablets of Losartan with various grades of hydroxyl propyl methylcellulose to restrict the drug release preferably in upper part of intestine and to improve its bioavailability and to provide constant drug plasma levels thereby improving the patient Compliance⁶.

Gastric emptying of dosage forms is an extremely variable process and ability to prolong and control emptying time is a valuable asset for dosage forms, which reside in the stomach for a longer period of time than conventional dosage forms. One of such difficulties is the ability to confine the dosage form in the desired area of the gastrointestinal tract⁷. To overcome this physiological problem, several drug delivery systems with prolonged gastric retention time have been investigated. Attempts are being made to develop a controlled drug delivery system that can provide therapeutically effective plasma drug concentration levels for longer durations, thereby reducing the dosing frequency and minimizing fluctuations in plasma drug concentration at steady state by delivering drug in a controlled and reproducible manner. Gastro retentive systems can remain in the gastric region for several hours and hence significantly prolong the gastric residence time of drugs⁶. Prolonged gastric retention improves bioavailability reduces drug waste and improves solubility of drugs that are less soluble in high pH environment, gastric retention to provide new therapeutic possibilities and substantial benefits to patients. The controlled gastric retention of solid dosage forms may be achieved by the mechanism of mucoadhesion, floatation, sedimentation, expansion, modified shape systems or by the administration of pharmacological agents, that delaying gastric emptying. Based on these approaches, floating drug delivery systems seems to be the promising delivery systems for control release of drugs.

Most of the orally administered dosage forms have several physiological limitations, such as GI transit time, incomplete drug absorption due to incomplete release of drug from the devices and too short residence time of the dosage forms in the absorption region of GI trac^t11. To overcome these limitations many attempts have been made by scientists by designing various drug delivery systems. Among these systems, Floating drug delivery systems (FDDS) is one of the approaches which remain buoyant due to their lower density that that of the GI and intestinal fluids. Both single and multiple unit systems have been developed, prolonged gastro retention of the therapeutic moiety may offer numerous advantages, including improvement of bioavailability, therapeutic efficiency and possible reduction of dose.¹²

NEED FOR THE STUDY:

In the recent years, a great deal of technological and scientific research has been carried out to the develop rate-controlled oral drug delivery systems in order to overcome physiological problems, such as short gastric residence times (GRT) and unpredictable gastric emptying times (GET). Gastro-retentive dosage forms will allow the delivery of restricted ‘absorption window’ drugs which are absorbed in a particular portion of the GI tract⁹

Floating drug delivery systems (FDDS) have a bulk density less than gastric fluids and remain buoyant in the stomach without affecting gastric emptying rate for a longer period of time. While the system is floating on the gastric contents, the drug is released slowly at the desired rate from the system. After release of drug, the residual system is emptied from the stomach. This will result in an increased GRT and a better control of the fluctuations in plasma drug concentrations. FDDS can be divided into two types¹⁴:

1. Non effervescent

2. Gas generating system

Gastro retentive drug delivery systems can remain in the gastric region for several hours and hence significantly prolong the gastric residence time of drugs. Prolonged gastric retention improves bioavailability, reduces drug waste, and improves solubility for drugs which are less soluble in a high pH environment¹².

Advantages of gastro retentive delivery systems: Floating drug delivery offers several advantages for drugs having poor bioavailability. These are given as follows¹⁴.

• Enhanced bioavailability

• Enhanced first-pass biotransformation

• Sustained Drug Delivery / reduced frequency of dosing

• Site-Specific Drug Delivery

• Reduced fluctuations of drug concentration

• Minimized adverse activity at the colon

• Absorption Enhancement.

Losartan is a competitive antagonist and inverse agonist of Angiotensin II. It is used in the treatment of hypertension. It bind to the AT1 receptor with high affinity and generally they are 10,000-fold more selective for the AT1 receptor than the AT2 receptor. It is potently and selectively inhibits most of the biological effects of Angiotensin II. Bioavailability of Losartan is about 33% and its half life is about 2.5hrs.

OBJECTIVE OF THE STUDY:

The principle of buoyant preparation offers a simple and practical approach to achieve increased gastric residence time for the dosage form and sustained drug release. Losartan is an orally active non-peptide angiotensin-II receptor antagonist, used in the treatment of hypertension due to mainly blockade of AT-I receptors. The main reason for low therapeutic effectiveness of Losartan is its narrow therapeutic index, poor bioavailability (25-35%), and short biological half life (1.5-2h). Conventional tablets should be administered 3-4 times to maintain the plasma drug concentration.

So, to increase therapeutic efficacy, reduce frequency of administration sustained release floating tablets of Losartan are prepared.

• To carry out compatibility studies between drug & polymers.

• To develop floating drug delivery system of Losartan potassium.

• To evaluate the formulation for various quality control parameters.

Procurement of material

Drug and HPMC K4M are obtained as gift of sample from Granule’s India limited Granules India Limited Temple road, Bonthapalli Jinnaram Mandal, Mandak District - 501 313

And Excipients are bought from Panchi chemicals private limited Mr. Rajendra Bhansali (Managing Director) 4-3-614, Tilak Road, Ramkote, Hyderabad - 500 001

Pharmacology

Mechanism of action:

Losartan competitively inhibits the binding of angiotensin II to AT1 in many tissues including vascular smooth muscle and the adrenal glands. Losartan is metabolized to its active metabolite, E-3174, which is 10 to 40 times more potent than Losartan and acts as a non-competitive AT1 antagonist¹⁵. Inhibition of angiotensin II binding to AT1 inhibits its AT1-mediated vasoconstrictive and aldosterone secreting effects and results in decreased vascular resistance and blood pressure. Losartan is 1,000 times more selective for AT1 than AT2. Inhibition of aldosterone secretion may increase sodium and water excretion while decreasing potassium excretion. Losartan is effective for reducing blood pressure and may be used to treat essential hypertension, left ventricular hypertrophy and diabetic nephropathy¹⁶.

Pharmacodynamics:

Losartan is the first of a class of antihypertensive agents called angiotensin II receptor blockers (ARBs). Losartan and its longer acting active metabolite, E-3174, are specific and selective type-1 angiotensin II receptor (AT1) antagonists which block the blood pressure increasing effects angiotensin II via the renin angiotensin-aldosterone system (RAAS)¹³. RAAS is a homeostatic mechanism for regulating hemo dynamics, water and electrolyte balance. During sympathetic stimulation or when renal blood pressure or blood flow is reduced, renin is released from granular cells of the juxtra glomerular apparatus in the kidneys. Renin cleaves circulating angiotensinogen to angiotensin I, which is cleaved by angiotensin converting enzyme (ACE) to angiotensin II. Angiotensin II increases blood pressure by increasing total peripheral resistance, increasing sodium and water reabsorption in the kidneys via aldosterone secretion, and altering cardiovascular structure. Angiotensin II binds to two receptors: AT1 and type-2 angiotensin II receptor (AT2). AT1 is a G-protein coupled receptor (GPCR) that mediates the vasoconstrictive and aldosterone-secreting effects of angiotensin II. Studies performed in recent years suggest that AT2 antagonizes AT1 mediated effects and directly affects long-term blood pressure control by inducing vasorelaxation and increasing urinary sodium excretion. Angiotensin receptor blockers (ARBs) are non-peptide competitive inhibitors of AT1. ARBs block the ability of angiotensin II to stimulate pressor and cell proliferative effects. Unlike ACE inhibitors, ARBs do not affect bradykinin-induced vasodilation. The overall effect of ARBs is a decrease in blood pressure16.

Pharmacokinetics:

Absorption : Well absorbed, the systemic bioavailability of Losartan is approximately 33%

Distribution : 34 L [Losartan] 12 L [active metabolite]

Protein binding: 99.7%, primarily to albumin.

Metabolism:

Hepatic. Losartan is metabolized to a 5-carboxylic acid derivative (E-3174) via an aldehyde intermediate (E-3179) primarily by cytochrome P450 (CYP) 2C9 and CYP3A4. E-3174 is an active metabolite with 10- to 40-fold higher potency than its parent compound, Losartan. Approximately 14% of Losartan is converted to E-3174: however, the AUC of E-3174 was found to be 4 – 8 folds higher than Losartan and

E-3174 is considered the main contributor to the pharmacologic effects of this medication.

Excretion:

After single doses of Losartan administered orally, about 4% of the dose is excreted unchanged in the urine and about 6% is excreted in urine as active metabolite. Biliary excretion contributes to the elimination of Losartan and its metabolites.

Half life :

The terminal t1/2 of Losartan is 2 hours and that of E-3174 is 6-9 hours.

Clearance:

Ø 600 ml/min [Healthy volunteers after IV administration] Renal Cl=56 + 1.0

Ø 23 ml/min [Hypertensive adults given 50 mg once daily for 7 days]

Ø Renal cl=53 + 33 ml/min [Hypertensive children (6-16 years old) given 0.7 mg/kg once daily for 7 days]

Drug interaction:

Amiloride : Increased risk of hyperkalemia

Drospirenone : Increased risk of hyperkalemia

Indomethacin : Indomethacin decreases the effect of Losartan

Lithium : Losartan increases serum levels of lithium

Potassium : Increased risk of hyperkalemia

Quinupristin : This combination presents an increased risk of toxicity

Rifampin : Rifampin decreases the effect of Losartan

Spironolactone: Increased risk of hyperkalemia

Tobramycin : Increased risk of nephrotoxicity

Tolbutamide : Tolbutamide, a strong CYP2C9 inhibitor, may decrease the metabolism and clearance of Losartan. Consider alternate therapy or monitor for changes in Losartan therapeutic and adverse effects if Tolbutamide is initiated, discontinued or dose changed.

Trandolapril : The angiotensin II receptor blocker, Losartan, may increase the adverse effects of Trandolapril.

Treprostinil : Additive hypertensive effect. Monitor antihypertensive therapy during concomitant use.

Triamterne : Increased risk of hyperkalemia

Experimental works:

Preformulation studies

1. Characterization of Losartan

· Oraganoleptic properties: the colour, odour and taste of the drug where recorded using descriptive terminology.

· Melting point: melting point of the drug was determined by capillary tube method.

· Solubility study: it is important to know about solubility character of a drug in system, since they must possess some limited aqueous solubility to elicit a therapeutic response. The solubility of drug was recorded by using various descriptive terminology specified in Indian pharmacopoea2007

2 Preparation and formulation of FDDS

Required quantity of bees wax was weighed and melted at 55 degrees in a large china dish over a water bath. The drug is added to the molten wax and mixed well. Previously weighed quantities of HPMC K4M, Ethyl cellulose and sodium bi carbonate were added to the drug-wax mixture and mixed well. After thorough mixing the china dish was removed from water bath and cooled. The coherent mass was then scrapped from the china dish and was passed through sieve no.60. The granules are then lubricated with talc and magnesium stearate is added. The lubricated granules were then passed through sieve no.100. The granules were then compressed using a single punch tablet machine.

Table 1: composition of Losartan in different formulations

Ingredients	F1	F2	F3	F4
Losartan	50mg	50mg	50mg	50mg
HPMC K4M	10mg	30mg	30mg	20mg
Ethyl cellulose	20mg	10mg	20mg	20mg
Sodium bicarbonate	30mg	30mg	20mg	30mg
Bees wax	40mg	40mg	40mg	40mg
Magnesium stearate	10mg	5 mg	5mg	5mg
talc	10mg	5mg	5mg	5mg

Sieving:

· Losartan was passed through sieve #60

· Polymers, magnesium stearate were added and passed through sieve#100

Dry mixing:

The above sieved materials were mixed thoroughly in a polythene bag.

Lubrication:

The resulting powder was lubricated with magnesium stearate and talc.

Compression:

· The lubricated powder was compressed using concave phased punches of 8mm diameter with 1.5pascal pressure in Cipla automated single punch machine.

· Parameters like average weight, hardness, friability, and thickness are checked during compression as in process quality measures.

3 Evaluation of sustained release matrix tablets of Losartan:

· Thickness: The thickness of the tablets where determined using a Vernier callipers. 10 tablets from each formulation where evaluated and average values were calculated.

· Hardness: For each type of formulation the hardness value of 5 tablets was determined using Monsanto hardness test apparatus.

· Friability: Friability of Losartan tested using Roche friabilator apparatus. A loss of less than 1% in weight was acceptable. The weight of 5 tablets was noted initially (W1) and placed in the friabilator for 4min/100rpm. The tablets were reweighed and noted as (W2). The difference in the weight is noted and expressed as percentage.

The friability percentage was determined using the formula:

Percentage Friability: = W1-W2 X 100

Where,

W1= initial weight of tablets

W2= weight of tablets after friability (usually < 1%)

4 In-vitro dissolution studies:

The In vitro dissolution studies were performed using USP-22 type-II dissolution apparatus at 100 rpm. dissolution test was carried out for a total period of 9hrs using 0.1N HCL (pH-1.2) solution (900ml) .an aliquot (5ml) was withdrawn at specific time intervals and drug content was determined using UV spectrometer at 274 nm .it was made clear that none of the ingredients used in matrix formulations interfered with the assay the release studies were conducted in triplicate.

RESULTS AND DISCUSSION:

Pre formulation parameters:

Characterization of Losartan

Ø Oraganoleptic properties:

White Colour, odourless crystalline powder

Ø Melting point:

Melting point value of Losartan was found to be 182^oC, 184^oC, and 187^oC. The reported melting point average for Losartan was found to be 184.33^oC. Hence experimental values are in good agreement with official standard values.

Table 2: solubility study of Losartan in various solvents

S. no:	Solvents used	Inference
1	Distilled water	Slightly soluble
2	0.1N HCL	Soluble
3	0.1N NaOH	Insoluble
4	Acetone	Slightly soluble
5	pH buffer	Slightly soluble

Table 2: list of raw materials

1	Losartan
2	HPMC K4M
3	Ethyl cellulose
4	Sodium bicarbonate
5	Bees wax
6	Magnesium stearate
7	talc

Procedure

Melt granulation technique:

Table 4: Data for calibration curve parameter of Losartan

S. No	Parameters	Values
1	Correlation coefficient	0.99
2	Slope	67.66
3	Intercept	0.206

Evaluation of sustained release matrix tablets

Ø Appearance : the tablets were observed visually and did not show any defect such as capping, chipping, and lamination

Ø Physical characteristics : the physical characteristics of the Losartan sustained release tablet (F1 to F9) such as thickness, diameter, hardness, friability, weight variation and drug contents were determined and results of formulation (F1 to F9) found to be within the limits specified in official standard books

Ø Diameter (thickness and diameter): thickness and diameter specifications may be set on an individual product basis excessive variation in tablet thickness and diameter can result in problems with packaging as well consumer acceptance. There were no marked so marked variations in the thickness and diameter of tablets within each formulation indicating uniform behaviour of granules throughout the compression process.

The size (diameter) of tablets of all formulations was found to be 8.00 + 0.0mm and thickness as 2.5mm

Ø Tablet hardness :

A difference in tablet hardness reflects in tablet density and porosity. In which turn are supposed to result in different release pattern of drug by affecting the rate of penetration of dissolution fluid after at the surface of tablet and formulation of gel barrier. The hardness of tablets was found to be in the range of 5.57 + o.37kg/cm² to 5.96 + 0.48kg/cm². This indicates good tablet strength.

Ø In-vitro dissolution studies :

The in-vitro dissolution studies were performed using USP-22 type-II dissolution apparatus at 100rpm. Dissolution test is carried out for a total period of 9 hrs using 0.1 N HCL (pH-1.2) Solution (900ml) for the rest of the period.

Table 5: In-vitro release drug profile of formulation F1

Time (hours)	Dissolution medium	% drug release	Amount (mg)
1	0.1 N HCL	0	0
2		6.041	17.04
3		30.422	52.84
4		55.322	93.25
5		76.267	134.62
6		95.071	168.52
7		------	-------
8		------	-------
9		------	-------

Discussion:

From the above table no. 7 it has been confirmed that dissolution rate is from 0-182.52

Table 6: In-vitro release drug profile of formulation F2

Time (hours)	Dissolution medium	% Drug release	Amount (mg)
1	0.1 N HCL	0	0
2		8.021	16.04
3		20.322	40.64
4		35.622	72.32
5		46.622	92.52
6		58.724	100.70
7		76.267	132.62
8		82.526	144.14
9		95.271	168.42

Discussion:

From the above table no. 7 it has been confirmed that dissolution rate is from 0-168.42

Table 7: In-vitro release drug profile of formulation F3

Time (hours)	Dissolution medium	% Drug release	Amount (mg)
1	0.1 N HCL	0	0
2		7.610	14.24
3		28.223	56.44
4		45.502	81.62
5		68.654	126.52
6		79.267	132.22
7		88.628	153.14
8		96.071	168.02
9		--------	--------

Discussion:

From the above table no. 7 it has been confirmed that dissolution rate is from 0-192.02

Table 8: In-vitro release drug profile of formulation F4

Time (hours)	Dissolution medium	% Drug release	Amount (mg)
1	0.1 N HCL	0	0
2		5.221	10.44
3		10.123	20.26
4		35.002	70.02
5		46.541	82.23
6		53.514	92.26
7		65.167	110.62
8		84.658	148.54
9		90.213	160.62

Discussion:

From the above table no. 7 it has been confirmed that dissolution rate is from 0-180.62

Table 9: comparative study of cumulative In-vitro % drug release of formulation F1 to F4

Time (hrs)	Dissolution medium	F1	F2	F3	F4
1	0.1 N HCL	0	0	0	0
2		6.041	8.021	5.221	5.221
3		30.422	20.322	10.123	10.123
4		55.322	35.622	35.002	35.002
5		76.267	46.622	46.541	46.541
6		95.071	58.724	65.167	53.514
7		-------	76.267	84.658	65.167
8		-------	82.526	96.213	84.658
9		-------	95.271	--------	90.213

Untitled

Figure 2 : comparative study of cumulative in-vitro % drug release curve of formulation F1 to F4

DISCUSSION:

Losartan is a water insoluble drug & its release from the matrix is largely dependent on polymer swelling, drug diffusion. The concentration of polymer in the sustained released layer was a key factor in controlling the drug release. Various sustained release formulations were formulated with ethyl cellulose, HPMC as binding agents and talc as diluents, magnesium stearate as lubricant.

In-vitro release studies of formulation F1, was prepared by ethyl cellulose with concentrations of 10:20:30 at the 6^th hour in which the release rate of F1 was found to be 95.07 +/- 1.01 at 6^th hour and 96.071 for F3 at the end of 8^th hour.

The release of F4 was found to be higher when compared to other formulations due to increase in the concentration of polymer.

The release of F2 was found to be higher than F4 when compared even to other formulations due to increase in the concentration of polymer.

From the above evaluation parameters it was concluded that the formulation F2 having a high percentage of drug release in a sustained manner, so the formulation F2 was selected as the optimised formulation.

DSC report from NISHIK laboratories

Nishka Lab Report

Measurement conditions employed Temperature range	0.450C
Heating rate [K/min]	10
Purge gas [Nitrogen]	60 ml/min
Protective gas [Nitrogen]	60 ml/min
Sample crucible	Aluminium pan with lid pierced and sealed

DCS result Conclusion from graph:

By observing the peaks in the graph from DSC result of pure drug and formulation F2 it was found that

1) The peaks in both the graphs were similar.

2) Additional peaks in the graph at 58⁰, 95^0, 113⁰ for formulation F2 is form the Excipients that were added at the time of formulation

3) Since the peaks from range 86.93⁰ of drug in both the graph were similar we can say that there was no drug and polymer interaction.

FTIR result Conclusion from graph:

By observing the peaks in the graph from FTIR result of pure drug and formulation F2 it was found that

4) The peaks in both the graphs were similar.

5) Additional peaks in the graph 520 cm^-1 to 1850 cm^-1 for formulation F2 is form the Excipients that were added at the time of formulation

6) Since the peaks from range 2800 cm^-1 to 3300 cm^-1 of drug in both the graph were similar we can say that there was no drug and polymer interaction.

Absorbance in 245 nm	Concentration microgram/ml
0.080	4.4
0.115	8.8
0.250	13.2
0.325	17.6

1	Electronic balance
2	Sipla Automated single punch machine
3	Roche Friability apparatus
4	Monsanto hardness tester
5	Vernier callipers
6	USP tablet dissolution apparatus type -II
7	UV spectrophotometer
8	Thermometer
9	Sieves No: 60 and 100
10	Disintegration apparatus
11	Tapping density apparatus

Measurement conditions employed Temperature range	0..450C
Heating rate [K/min]	10
Purge gas [Nitrogen]	60 ml/min
Protective gas [Nitrogen]	60 ml/min
Sample crucible	Aluminium pan with lid pierced and sealed