Saraf Swarnlata*, Saraf S1, and Dixit V.K. 2
1Institute of Pharmacy, Pt. Ravishankar Shukla University, Raipur (CG) 492 010
2Department of Pharmaceutical Sciences, Dr. H.S. Gour V.V., Sagar, M.P.
Transdermal delivery of timolol meliate was tried for both reservoir as well as matrix system. The physically stable patches regarding drug contents, tensile strength, toughness and WVT were found for PVA10 and HE2 formulation. Both patches follows diffusion controlled drug permeation and high permeation with PVA10 while reservoir system follows zero order permeation kinetics.
Timolol maleate is a beta adrenoceptor-blocking agent used in treatment of cardiovascular diseases like myocardial infarction, angina pectoris, hypertension, respiratory complications and migraine. It is 8-10 times potent than propranolol 1. The main limitation of therapeutic effectiveness of timolol maleate is its higher frequency of drug dosing and short biological half-life, high first pass metabolism and poor bioavailability by oral route. . It is rapidly absorbed from gastrointestinal tract with peak plasma concentration of 5-10 ng/ ml after 1 hr2, it is metabolized up to 80% in liver with a mean half-life of 2.0-2.5 hr.3, thus necessitating frequent administration of larger doses to maintain therapeutic drug level. Therefore, To maintain effective plasma concentration and to avoid sub therapeutic and toxic concentration, a continuous delivery of timolol maleate is required. The transdermal route is, therefore, a better alternative, to achieve constant plasma level, which additionally warrants less frequent dose regime.
The present study has been selected transdermal delivery system to achieve maximum therapeutic benefit.
MATERIALS AND METHODS
Gift sample of timolol maleate (TM) was obtained from Cadila Antibiotics Ltd., Ahamdabad. Hydroxy propyl methylcellulose was procured from Warner Hindustan Ltd., Hyderabad. Dibutyl phthalate, ethyl cellulose, polyvinyl alcohol (PVA), HEPES buffer, procured from Sigma Chemical Co. St. Locus Mo, USA. All other chemicals and regent used were of analytical reagent grade.
Fabrication of matrix diffusion patches
Matrix patches were casted4 on mercury using stainless steel rings having inner diameter of 1.5 cm and thickness 0.5 cm were used for holding the polymer solution on mercury surface. Two type of polymer patches were prepared; HPMC and EC combination and with PVA. The polymer solutions were prepared by dissolving HPMC 10% ands EC 10 % separately in methanol- chloroform (1:1) mixture. Both solutions were mixed together in combination of 1:9, 2:8, 3:7, 4:6 and 5:5 respectively using 1% dibutyl phthalate as plasticizer. A weighed amount of drug is dispersed in polymer mixture then poured in ring placed on mercury surface in petri dish at a uniform place and solvent evaporation was controlled by conveying with funnel. After evaporation of the solvent, the film was taken out from the metal ring by sharp knife and preserve in aluminum foil. Similar procedure was adopted to prepare PVA matrix patch preparation having polymer concentration of 5, 10.and 15% in water with 0.5% glycerin as plasticizer.
Thickness of polymeric patch was measured by using a dial gauge (Mercer, England), having least count of 0.002 mm. To maintain its shape, enough hardness is required to resist independence or penetration was determined by Hall’s method4 and calculated as a functional weight. In order to determine the elongation as a tensile strength, the polymeric patch was pulled by means of a pulley system; weights were gradually added to the pan to increase the pulling force till the patch was broken. The elongation i.e. the distance traveled by the pointer before break of the patch was noted with the help of magnifying glass on the graph paper5, the tensile strength was calculated as kg/ cm2. The presence of moisture may not affect the hardness of patch in the normal environmental conditions, but it may affect in exaggerated conditions. The polymer patches were cut, weighed and placed in a humidity chamber maintained at 68% RH for 72 h for equilibrium. After 72 h polymer patch were taken out and weight accurately. The difference between initial and final weight was computed as percentage moisture absorbed. The water vapor transmission (WVT) from the film was calculated by Crowfold and Esmeric formula 6. It was determined at 25+ 20C at 68%RH. Glass weighing bottles of equal diameter (2.5 cm) and height (5.0 cm) were used as WVT cells. A weight quantity of anhydrous calcium chloride was taken up to 10 mm height in each cell and a thin layer of silicon adhesive grease applied over the brim then patch was placed on brim and adhesive was allowed to set for 5 minutes. The cells are accurately weighed and kept in humidity chamber maintained at 68% RH for 24 h. After 24 h, the cells were again weighed and an increase in weight was considered as a quantitative measure of the moisture transmitted through the patch. Drug distribution studies: The distribution of drug in polymer patch effect the release rate. It was studied microscopically with the help of Lietz Microscope to observe uniform distribution of drug in patch.
Stability studies of all patches were performed at different storage condition by measuring tensile strength, moisture content and drug content (spectrophotometric method). The measurement were carried out by keeping the patches at different conditions of temperature 280C, 350C and 500C and relative humidity of 30%, 50%, 68 % for storage period of three months at room temperature (25±10C). The patches, which maintained uniformity, shape, toughness, drug content and flexibility at all temperature and RH, were selected for further permeation studies.
The full thickness human cadaver skin was washed with purified water after removal of all subcutaneous fat and hairs and cut in to pieces for experimental use. The skin pieces were soaked in HEPES buffer and store in freezer at 300C until used. Just before the experiment, it was thawed at room temperature and checked for any microscopical damage.
In vitro drug permeation studies:
A drug permeation study was carried out with drug solution in HEPES buffer pH7.4 and stable patches through human cadaver skin using modified kieshry- chein diffusion cells. The concentration of drug kept similar in drug solution in HEPES buffer and patches to compare permeation profile. The Patches and drug solution were kept on stratum cornium side of cells and this patch - skin - complex sandwiched between donor and receptor compartment. The receiving compartment contains blank 10.0 ml of HEPES buffer pH 7.4 and touches the dermal side of the skin. The whole of the assembly was kept on magnetic stirrer, which thermostatically controlled at 37+ 2oC at 100 rpm. Samples were withdrawn at pre set time interval from the receiving compartment and analyzed spectrophotometrically at 294 nm using shimadzu-1601 UV- visible spectrophotometer. The fresh buffer in receiving compartment was replaced after each withdrawal. The permeation studies determined for period of 4 h. and calculated as cumulative percent drug permeated.
In present studies, the polymer and plasticizer choice for patch preparation were based on no interaction with drug and HEPES buffer with considerable stability. Various combinations of polymers hydroxy propyl methyl cellulose (HPMC) and ethyl cellulose (EC) and various concentration of polyvinyl alcohol were tried for patch preparation and evaluated for physical studies (Table 1).
|Formulation Code||Polymer Used||Polymer Core % w/v||Thickness
gm/cm2 / 4 h
Table 1: Physical evaluation of polymeric patch of Timilol maleate
The main physical evaluations considered for stability were WVT rate, tensile strength and % moisture absorption and drug content. The polymer patch prepared with combination in the ratio of 2:8 HPMC and EC (HE2), PVA of 10% w/v (P10) were found to be satisfactory at all temperatures and relative humidity. On the basis of physical and stability studies, the patches HE2 and PVA10 were considered for permeation studies. The in- vitro permeation studies of drug solution and patches were performed to observe permeation profile. The permeation profile of both solution and patches were compared
The in- vitro stability studies of all patches were performed in terms of stability against storage conditions and aging effect, because TM is a drug used for long therapy to maintain its therapeutic effect especially when used as antihypertensive agent. The physical characterization like tensile strength, moisture absorption and WVT rate and drug content were main parameter for stability studies, which revealed no appreciable changes occurred in patches (HE2 & PVA10) at normal storage conditions (250C+1). The drug solution permeation profile suggests that it followed Fick’s law of diffusion. Linear relationship between cumulative percent drug permeated verses time indicate zero order permeation of drug through human cadaver skin with lag time 35 minutes. The transdermal permeability coefficient of TM was calculated to be 323x10-5 +0.02cm2/h from the steady state portion of the curve (Fig.1).
The permeation profile of drug from both patches HE2 and PVA10 when plotted,between permeation data against square root of time shows linear relationship indicating drug permeation followed Higuhi equation (Fig.2).
The permeation profile
data of patches were plotted in log values with time, the slope value comes
near to 0.49+0.01SD (~ 0.5), suggesting drug permeation is controlled by diffusion
within the matrix rather than by skin.
When we compare both patches, the PVA10 system provide higher 1.589 + 0.20 SD % drug/ cm2 of permeation rather than HE2, i.e., 0.987 +0.20 % drug/ cm2 in 4h of period.
The studies suggest that both reservoir as well as matrix system of transdermal delivery of TM is possible. The reservoir system followed zero order while the matrix system followed first order release profile. Among both matrix systems PVA10 patch have more permeability than HE2 patch.
1. Napolian, L. A., Smith, R. L., Proceed. Int. Symp, Controlled Release Bioact. Mater., 17, Controlled Released Society Inc. USA 1990, Abst. No. D220.
2. Remington Pharmaceutical Sciences, 18th Ed., Mark Publishing Company, Pennsylvania, 1990, P 1676.
3. Vermeji P. J,. Pharm. Pharmacol, 1978, 50,53.
4. Sciarria, J. J., Patel, S. P., J. Pharm. Sci., 1975, 64, 128.
5. Allen, D. J., DeHerco J. D., Kwan, K. C., J. Pharm. Sci., 1972, 61, 107.
6. Crawford, R. R., Esmerian, O. K., J. Pharm. Sci., 1971, 60, 314.
First Published February
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