INTRODUCTION:

Modified release dosage form show different release profiles depending on its type. This dosage form is used to describe products that alter the timing and rate of release of drug substance. Pulsatile drug delivery system is the most interesting time dependent system. Bioadhesive Pulsatile Drug Delivery Systems are gaining a lot of interest as they deliver the drug at the right site of action, at the right time and in the right amount as well as they have capacity to bind to the mucus membrane thus prolongs retention time in the Gastro-intestinal tract resulting in maximum absorption and hence enhanced bioavailability and spatial and temporal delivery and increasing patient compliance.

The release of the drug as a pulse after a lag time has to be designed in such a way that a complete and rapid drug release follows the lag time¹. Pulsatile drug delivery system is an important and focusing part among time-controlled release systems. It is characterized by a predetermined lag time period in the beginning stage of drug release followed by a burst drug release phase in the drug release profiles^2-4. The pulsatile release has some advantages like it can avoid drug tolerance and control of tissue and the drug release can be controlled by time, by site or by combination of both parameters^5,6. As far as coating technology is concerned, compression coating is the most popular method to achieve pulsatile drug release due to the simplicity of the formulation process compared to the traditional liquid coating processes which are time-consuming and often not solvent-free. Compression-coating provides thick coatings within short processing time which can contribute in maintaining the desired lag time for achieving chrono-pharmacotherapy^7-9. Bioadhesive drug delivery system is a strategy to prolong the residence time of various drugs on gastrointestinal surface and bioadhesion defined as ability of material to adhere the biological tissue for an extended period of time^10-11. Drugs having maximum absorption in stomach or unstable in intestine are preferred for bioadhesive drug delivery system¹². Bioadhesive pulsatile drug delivery will be more beneficial for drugs which need pulsatile release in stomach¹³. The oral controlled-release drug delivery shows a specific pattern of drug release in which the concentration of the drug is maintained in the therapeutic window for an extended period of time, thereby imparting sustained therapeutic action. But in case of certain diseases that follow circadian rhythm which demand engineered specificity for the release of drug in a burst manner after a predetermined lag time for the treatment of hypertension associated with circadian rhythm^14-15.

Lisinopril is a synthetic peptide derivative, is an oral long-acting angiotensin converting enzyme inhibitor (ACE)¹⁶. It is widely used in treatment of hypertension; it has the biological half-life of 12.6 hr. Its bioavailability is 25% and it is mainly excreted in urine^17-18. So in this present investigation attempt was made to develop bioadhesive pulsatile tablet of lisinopril which can be prove promising approach to treat cardiac disorder associated with circadian rhythm.

MATERIAL AND METHODS:

Material:

Lisinopril was obtained as a gift sample from Cipla India ltd, Mumbai India, HPMC K100M was gifted by bright lab, Hyderabad; Cabopol was gifted by Dr Reddys Lab, Hyderabad; lactose, magnesium Stearate, Microcrystalline cellulose, Crosscaramellose, Mannitol was purchased by Unique Chemicals. All other chemicals and solvents used were of pharmaceutical and analytical grade. Double distilled water was used throughout the study for all the experimental procedures.

Preparation of Lisinopril core tablet and its characterization:

Preparation of Lisinopril core tablet:

The inner core tablet of Lisinopril was prepared by direct compression method. To fix concentrations of superdisintegrant in the tablets, different preliminary batches of core tablets were taken. The concentration of superdisintegrant was varied from 2–8mg in core tablets from formulation C1 to C4 (Table 1). The powder mixtures of lisinopril, Crosscaramellose sodium, microcrystalline cellulose and lactose were dry-blended for 20min and then finally magnesium stearate was added. The mixtures were then further blended for 10 min. 100mg of the resultant powder blend was compressed using a rotary tablet machine (Shakti) with an 8-mm punch¹⁹. The formulation chart of lisinopril core tablets shown in table no. 1

Table No.1 Formulation chart for lisinopril core Tablet

Batch Code/ Content	C1	C2	C3	C4
Lisinopril	20	20	20	20
Crosscaramellose	2	4	6	8
Microcrystalline cellulose	25	35	45	55
Lactose	43	31	19	7
Magnesium stearate	5	5	5	5
Talc	5	5	5	5
Total (mg)	100	100	100	100

Characterization of the core tablet:

Evaluation of various pre-compression and post-compression properties of core tablets:

The powder blend of core tablet was evaluated before compression for various parameters like bulk density, tapped density, Carr’s index and Hausner’s ratio to confirm powder blend suitability for direct compression. The core tablets prepared by direct compression were subjected to evaluation of properties including drug content uniformity, weight variation, tablet hardness, friability, thickness etc. as per the standard procedure. The results of pre-compression and post-compression properties are shown in table 3 and table 4 respectively. The different core tablets of lisinopril were added to the dissolution medium. The dissolution study was performed in 0.1 N HCL (pH 1.2). The dissolution study was carried out using USP type- II apparatus (EDT 08LX Electrolab) at 37+0.5°C and 100rpm paddle speed. The samples were withdrawn from dissolution media at a specified time interval up to 60min and the absorbance of the sample was recorded using UV spectrophotometer (Shimadzu UV spectrophotometer 1800) at 206nm.

FT-IR study for drug excipient compatibility:

FT-IR has been employed as a useful tool to identify drug excipient interaction. Samples were analyzed by the potassium bromide pellet method in an IR spectrophotometer (Alpha T Bruker) in the region from 4000 to 400 cm^-1. The FT-IR studies were carried out for pure lisinopril, lisinopril and HPMC K100M, lisinopril with all excipient together and final crushed tablets. The scans were evaluated for the presence of principle peaks of a drug, shifting and masking of drug peaks and appearance of new peaks due to polymer interaction. The FT-IR spectra of lisinopril and the physical mixture of all polymers together are shown in figure No.2

Preparation of Press-coated bioadhesive pulsatile release tablet (BPRT):

The optimized core tablet was used for the preparation of the Bioadhesive Pulsatile Release Tablet. An erodible outer shell contained HPMC K100 M, Cabopol, Magnesium Stearate, talc, Mannitol as barrier layer. Half of the barrier layer material was weighed and transferred into a 13-mm die, then the core tablet was placed at the center, and the remaining half of the barrier layer materiel was added into the die. The tablets were compressed on KBR at a pressure of around 3 tonns. The process of press coating proceeds in the following order as Shown in Figure no.1a. Prefilling half amounts (80 mg) of outer coating materials into the die b. Core tablet (80 mg) is placed on the powder bed of outer coating material c. Centering d. Filling the residual half amounts (80 mg) of outer coating material e. Compression f. Ejection of press coated tablet from the die. The formulation chart of lisinopril press coating of bioadhesive pulsatile release tablet (BPRT) shown in table no. 2

Figure No.1 Process of press coating of bioadhesive pulsatile release tablet (BPRT)

Table No.2 Formulation chart for lisinopril core Tablet

Batch Code/ Content	F1	F2	F3	F4	F5	F6	F7	F8
Lisinopril core tablet	100	100	100	100	100	100	100	100
HPMC K 100 M	50	60	70	80	90	100	110	120
Carbopol	60	60	60	60	60	60	60	60
Magnesium Stearate	10	10	10	10	10	10	10	10
Talc	10	10	10	10	10	10	10	10
Mannitol	170	160	150	140	130	120	110	100
Total (mg)	400	400	400	400	400	400	400	400

Evaluation of various tablet properties of bioadhesive pulsatile release tablet (BPRT):

The Press-coated tablets prepared by direct compression were subjected to evaluation of properties including, weight variation, thickness, tablet hardness, friability etc as per the standard procedure

In vitro Mucoadhesion test:

In first study a tablet was fixed on glass box. To the upper glass slide mucus membrane was fixed and to it a thread was tied and the thread was passed down through a pulley, the length of the thread from the pulley to the pan was 12cm. At the end of the thread a pan of weight 17g was attached into which the weights were added. The glass slide was placed on the tablet with weight (17g) for 1 min. The weight require to detach the tablet from the glass box (muco-adhesive strength) was determined. In second study only change was made that tablet was just placed and not fixed on glass box. Time required to detach the tablet from the mucus membrane (adhesion time) was recorded. The force of adhesion was calculated using following formula;

Force of adhesion (N)

= Mucoadhesive strength/100 × 9.81 ………(Eq 1)

In-Vitro dissolution study of bioadhesive pulsatile release tablet (BPRT):

The dissolution studies of Bioadhesive pulsatile release tablet (BPRT) of Lisinopril were performed by using USP paddle type 2 dissolution test apparatus, in 900ml of 0.1N HCL (pH 1.2). Temperature was maintained at 37±2°C and 100rpm stirring was provided for each dissolution study. The BPRT equivalent to 20mg of Lisinopril was used for each dissolution study. Samples were collected periodically and replaced with a fresh dissolution medium. After filtration through Whatman filter paper 41(poresize 25µm), concentration of Lisinopril was determined by UV visible spectroscopy as specified in yield and drug content at 206nm. The dissolution profiles of various bioadhesive pulsatile release tablet batches are shown in Figure no.3

Stability study:

The optimized formulation was subjected for six-month stability study with the help of stability chamber (Remi SC-19 Plus) by storing tablets from the optimized batch in an ambered colored screw-capped glass bottles at accelerated and controlled temperatures 40°C and relative humidities (75%) for a period of 6 months^20-22. After specific interval, placed sample were analyzed for physical appearance, Drug content, In-vitro dissolution study, Hardness, Thickness.

RESULT AND DISCUSSION:

Evaluation of various tablet properties of core tablets:

Evaluation of pre-compression parameters core tablet blend:

The physical mixtures as per formulas of various batches of core tablets were evaluated for the flow properties before compression. The values of bulk density, tapped density, Carr’s index and Hausner’s ratio were calculated and depicted in Table No.3. From the physical properties of the powder blends of various batches of core tablets, it was confirmed that all of them are suitable to formulate the tablet using direct compression technique. The bulk density and Tap density of powder blend for core tablet batch C3 was found to be 0.394g/mL and 0.437g/mL respectively (Batch C3 considered for reference). As the values of Carr’s index shown 09.30%, which means it has excellent compressibility and showed passable flow property, which is again confirmed by the Hausner’s ratio which was found to be 1.10

Table No. 3 Various pre-compressional parameters core tablet blend

Powder property	Batch Code
Powder property	C1	C2	C3	C4
Bulk density (g/mL)	0.424 ± 0.011	0.407 ± 0.015	0.394 ± 0.010	0.372 ± 0.013
Tap density (g/mL	0.464 ± 0.019	0.448 ± 0.016	0.437 ± 0.011	0.418 ± 0.014
Carr’s index (%)	08.69 ± 0.37	09.09± 0.27	09.30± 0.29	09.75± 0.31
Hausner’s ratio	1.02 ± 0.04	1.10± 0.05	1.10± 0.07	1.13± 0.09

Evaluation of post-compression parameters of core tablets:

The core tablets from each batch were evaluated for Average weight, Thickness, disintegration time, Drug content, Hardness and % Friability. The tablets showed good weight uniformity as indicated by the low value of Relative Standard Deviation (RSD< 1%), The Tablet thickness was found in range from 1.95±0.08mm to 2.10±0.07mm, The core tablets which contains 6mg disintegrant in its composition show disintegration time of 59 sec which was closer to core tablet composition containing 8mg disintegrant hence core tablet batch C3 was further used to develop press coated pulsatile tablet. The Drug content uniformity of the Tablet was found to comply with the official specification, as the assay value found to in range between 97.25±0.15 to 99.28±0.24 of the theoretical value. The tablet Hardness varied from 3.4±0.2 to 3.7±0.3 which was sufficient for core tablet as it compressed again in the subsequent step of the pulsatile formulation. The tablets passed the friability test, as all the batches were within the pharmacopeial limit (F< 1%). The dissolution study was carried out in 0.1N HCl as bioadhesive pulsatile formulation expected to be released in the stomach after a specific lag time. The all batches of core tablets showed almost complete drug release in acidic pH. Hence core tablet batch C3 which showed optimum disintegration time further considered for compression as bioadhesive pulsatile release tablet (BPRT). The results of various post-compressional parameters are reported in table No.4.

FT-IR study for drug excipient compatibility:

FTIR Spectra of pure lisinopril, lisinopril and HPMC K100M, lisinopril with all excipient together and final crushed tablets were shown in Figure no.2. The FT-IR spectrum of drug and polymers revealed that major frequencies of functional groups of pure drugs remain intact or slightly shifted in physical mixture, coating material and final formulation; hence there was no major interaction between the drug and polymer used in the study. The FTIR spectra of lisinopril along with all excipients used for compression coating and in core tablet does not show any appreciable change in the characteristics of pure drug indicating various polymers used for formulation were compatible with lisinopril.

Evaluation of various tablet properties of press-coated tablets:

The press-coated bioadhesive pulsatile release tablets (BPRT) from each batch were evaluated for Average weight, thickness, Hardness and % Friability. The tablets showed good weight uniformity as indicated by relative Standard which was as per the official limits. The Tablet thickness was found in range from 3.55 ± 0.09 mm to 4.10±0.16mm.

The Drug content uniformity of the core tablets was assessed for core tablets which were as per the standard specification and same core tablets were used for formulating bioadhesive pulsatile release tablets. The tablet Hardness varied from 6.4±0.2 to 7.7±0.2 which was acceptable for the pulsatile tablet as drug release expected to be released after the specific lag time. The tablets also passed the friability test, as all the batches were within the pharmacopeial limit (F< 1%).

In-vitro Mucoadhesion test:

The in-vitro mucoadhesion study was carried out for three parameters which were adhesion time, mucoadhesion strength and force of adhesion. The adhesion time ranging from 4.15±0.51 to 7.45±0.58, the mucoadhesion strength ranging from 28.12±0.08 to 39.45±0.13 and force of adhesion ranging from 2.52± 0.2 to 6.05±0.2. The overall results obtained from in-vitro mucoadhesion study were satisfactory to prove prepared formulations were suitable to adhere for longer duration of time to stomach mucosa and hence it will be suitable for chronotherapy.

In-vitro dissolution study of bioadhesive pulsatile release tablet (BPRT):

At the end of 11 hrs the mean % drug release of batches F1, F2 and F3 was found to be 73.08±0.91%, 75.2±0.45%, 79.92±2.30% respectively. As the polymer concentration increases drug release was decreased and vice versa. Higher concentration of polymer reduces free water volume and increase viscosity of the tablet coat causes reduction in drug release. In above results we found higher concentration of polymer in batch F8 and it shows decreased drug release. At the end of 11 hrs the mean % drug release of batches F4, F5 and F6 was found to be 88.26±1.43%, 94.03±2.92% and 97.15±2.60% respectively. The batch C6 shows 97.15% drug release which was maximum. Due to appropriate concentration of both polymers HPMC and Carbopol, gives maximum drug release after definite lag time. Based on the results the batch C6 gives satisfactory results and used for the stability study. The cumulative percent drug release of lisinopril compressed coated tablet formulation C7 and C8 was shows zero percent drug release at the time of 2 hr and shows drug release 88.03±0.07 and 81.80±2.40 at the end of 7 hrs respectively, because of maximum concentration of both polymers HPMC and carbopol these C7 and C8 batch gives decreased drug release and increase in lag time. It also indicates that the formulations were showed drug release in pulsatile manner and hence suitable for chronotherapy of cardiac disorder. From the dissolution profile of various batches, it was clearly indicated that concentration of polymers namely HPMCK100M and Carbopol directly affects on lag time and overall drug release. The dissolution profile of various batches shown in figure no.3

Figure No. 3 In-Vitro dissolution studies of press-coated bioadhesive pulsatile release tablets a) Batches F1, F2 and F3 b) batches F4,F5 and F6 c) batches F7 and F8

Stability study:

The stability study was conducted for an optimized check-point batch (F6) to study various important parameters. A stability results clearly indicate that developed pulsatile product was sufficiently stable under accelerated and controlled conditions. No significant change in physical appearance and other parameters including hardness, Thickness, weight variation and Drug content indicates press coated bioadhesive pulsatile release tablet was found stable under accelerated temperature conditions. The results of various parameters studied after the specific interval of time are depicted in table no.5

Table No. 5 Results of stability study of optimized-check point batch (F6)

Parameter/ Time interval	Hardness Kg/cm² [n=3]	Thickness (mm) [n=3]	Drug content (%) [n=3]
Initial	6.9± 0.7	4.10 ± 0.13	99.28± 0.24
After 1 Month	6.8± 0.4	4.12 ± 0.10	99.70± 0.13
After 2 Month	6.8± 0.5	4.11 ± 0.12	100.28± 0.84
After 3 Month	6.9± 0.4	4.11 ± 0.14	98.70± 0.24
After 6 Month	6.9± 0.2	4.11 ± 0.11	99.13± 0.19

CONCLUSION:

The present study demonstrates the successful preparation of press-coated bioadhesive pulsatile release tablet of antihypertensive drug lisinopril with an aim to treat the heart diseases which follows a circadian rhythm. The core tablets prepared by using various concentrations of disintegrants found suitable for complete release of drug in acidic medium indicating its solubility in gastric fluid. The FT-IR studies indicate that selected polymers are compatible with lisinopril since no interaction found in drug-excipient compatibility studies. The prepared bioadhesive pulsatile release tablet found to be releasing its drug in pulsatile manner and use of Carbopol showed sufficient bioadhesion. The said formulation is to be taken around 22:00 pm after dinner which will provide an ideal therapeutic regimen with enhanced patient compliance Thus, the developed pulsatile tablet can be considered to be a promising formulation for the relief of early morning surge in blood pressure and other cardiac disorders which follows a circadian rhythm.

ACKNOWLEDGMENT:

Authors are thankful to the Cipla India ltd, Mumbai India for providing gift sample of lisinopril. The Shivaji University, Kolhapur and D.Y. Patil University are acknowledged for assistance with analytical work.

CONFLICTS OF INTEREST

None.

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Received on 29.05.2021 Modified on 27.07.2021

Research J. Pharm. and Tech. 2022; 15(7):3057-3062.

DOI: 10.52711/0974-360X.2022.00511

Batch code	Average weight (mg) [n=20]	Thickness (mm) [n=3]	Disintegration Time (Sec) [n=3]	% Drug Content [n=3]	Hardness Kg/cm²[n=3]	% Friability
C1	101.50 ± 0.51	2.10 ± 0.07	120± 2.12	97.25 ± 0.15	3.7 ± 0.3	0.80
C2	100.75 ± 0.75	1.95 ± 0.08	95± 1.50	99.28± 0.24	3.6 ± 0.6	0.86
C3	99.50 ± 0.58	2.10 ± 0.09	59± 1.15	98.45 ± 0.56	3.7 ± 0.2	0.39
C4	99.24 ± 0.74	2.00 ± 0.11	58± 1.65	99.24 ± 0.20	3.4 ± 0.2	0.38