Pharmaceutical compositions containing trapidil, and process for their preparation

Abstract: Controlled release oral pharmaceutical composi­ tions, containing Trapidil, characterized by the use of hydroxypropylmethylcellulose having suitable viscosity and functional groups contents as base carrier, and of an organic acid to balance the pH, are described.

Description: The present invention refers to a pharmaceutical composition for oral administration containing Trapidil and to a process for the preparation thereof. Trapidil, i.e. 5-methyl-7-diethylamino-5-triazole-[1,5-a]-pyrimidine, is a substance having a wide spectrum of pharmacologic and biochemical activities on the circulatory system: dilatation of large coronary arteries and collateral pathways, development of inter-arteriolar coronary anastomosis, inhibition of phosphodiesterase, inhibition of platelet aggregation and inhibition of thromboxane A₂ synthesis. It is indicated for the treatment of conditions of reduced artery perfusion and platelet hyper-aggregation, where a circulation improvement and an anti-thrombotic activity are required. In particular: ischaemic cardiopathy, chronic cerebral vasculopathies, consequences of myocardial infarct and of cerebral ictus. After oral administration, Trapidil is quickly absorbed, reaching maximum plasmatic concentration 1 hour after administration. Hematic level then decreases rapidly, reducing to half in 90 minutes and after about 10 hours there is an almost total disappearance of the active principle from the blood. The half-life period is equally short (1.5 - 1.7 hours). The drug is quickly metabolized and eliminated through urines. Two metabolites derive from the loss of 1 or 2 ethyl residues (TP1 and TP2), of which the first reaches maximum serum concentration already 3 hours after administration, but it then decreases rapidly. The TP1 metabolite is endowed with cardiovascular activity. Studies conducted in mice show in fact that said compound causes an increase in the coronary flow and relaxation of the isolated coronary artery. Fast metabolization of Trapidil and fast elimination of the TP1 metabolite cause a quick disappearance of the two active principles from the circle thus making frequent drug administrations necessary over the time. This clearly causes upset to the patient, who often has to take other drugs at the same time, especially when considering the fact that it is a drug for long term treatments. Therapeutic advantages deriving from the use of pharmaceutical preparations having a prolonged release of the active principle, regarding frequency of administration, reduction of side effects and maintenance of effective hematic concentration have been recognized. Object of the present invention is an oral controlled release pharmaceutical composition containing Trapidil as active ingredient, which grants to the organism the right drug amount for an extended period of time sufficient to obtain the desired pharmacological response with a simplified posology (2 administrations/die). A first object of the invention is an oral pharmaceutical composition containing as base carrier a mixture of hydroxypropylmethylcellulose and methylcellulose or other cellulose ethers characterized in that the solid carrier material is in an amount comprised between 30% and 50% by height of the active principle with the proviso that the amount of the cellulose ether is not less than 30% by weight of the mixture and with conventional excipients for tablets, such as lactose, magnesium stearate, silica or, in general, binding, lubricating, disintegrating agents and similar. Hydroxypropylmethylcelluloses are available in various grade under different trade names. The use of cellulose derivatives such as hydroxypropylmethylcellulose in pharmaceutical formulations has long been known, (US-B1-4389393). EP-A-205336 and EP-A-207638 disclose sustained release pharmaceutical compositions comprising hydroxypropylmethylcellulose and a polymeric component which is reported to be critical for the release characteristics of the compositions. GB-A-2163648 discloses "floating" compositions based on a combination of a solid fat or oil with a cellulose derivative. EP-A-187433 discloses powder compositions suited for the nasal or buccal administrations of steroids or glycyrrizic acid derivatives, comprising cellulose ethers as carriers. The properties of these cellulose ethers, obtained by substitution of cellulose hydroxyl with methoxy groups and by further introduction of hydroxypropyl groups, are a function of the substitution degree, distribution and type of the substituents, which determine solubility and viscosity degree. Therefore the selection of certain cellulose ethers or their mixtures as base carrier is quite important in the preparation of controlled release pharmaceutical compositions. Cellulose ethers such as hydroxypropylmethylcellulose are hydrophilic and tend to absorb water from the surrounding environment. For an effective controlled release of the active principle, hydration degree and rate of the matrix, expressed also as viscosity degree, must be evaluated in correlation to the solubility of the drug. Other elements influencing the release pattern of the active ingredient are the composition of the carrier base material, its weight ratio with the active principle and the degree of compression of the mixture. It has now been found, and it is the object of the present invention, that controlled release pharmaceutical compositions of Trapidil can be obtained when using as a carrier matrix a mixture of a hydroxyprophylmethylcellulose containing an average of 22.1% by weight of methoxy groups and an average of 8.1% by weight of hydroxypropoxy groups and whose viscosity degree (viscosity of 2% aqueous solution at 20°C) is comprised between 10⁻² Ns/m² and 100 Ns/m² (10 and 100,000 centipoises), selected from the commercially known ones such as Methocel® K 100, K 4 M, K 15 M or K 100 M, combined with another cellulose ether such as methylcellulose, in an amount not less than 30% of the mixture. Particularly advantageous has proven to be furthermore the addition to the composition of an acidifying agent consisting of an organic acid such as tartaric, malic, maleic, malonic or citric acid (preferably citric acid) to provide, when the active principle is released, a microenvironment with acid pH, thus reproducing the most favourable conditions for absorption of the drug that is rapidly absorbed at gastric level from conventional compositions. The preparation of the pharmaceutical compositions of the invention is simply made by direct compression of the components, previous granulation of the mixture of the active principle plus citric acid, if present. A second aspect of the invention refers to a process for the preparation of oral, controlled release pharmaceutical compositions containing Trapidil. Spray-dried lactose, hydroxypropylmethylcellulose, optionally combined with methylcellulose, and magnesium stearate are added to a mixture of Trapidil and silica suitably sieved. The various ingredients are mixed and then compressed. When citric acid is added, a mixture of this and Trapidil is prepared and is then granulated with water. The pre-sieved silica and the other components are added to the sieved and dried granulate. All the ingredients are mixed and then compressed. The examples wich follow illustrate the invention in more details without limiting it in any way. The amounts indicated in the examples are for the preparation of 10,000 tablets. The active principle dosage can vary between 100 and 300 mg per unit: the examples refer to a unit dose of 200 mg. EXAMPLE 1 Preparation of tablets containing 200 mg of active principle with no addition of citric acid. 2.0 Kg of Trapidil and 0.020 Kg of precipitated silica were placed into a stainless steel cubical mixer of a 8 l total capacity rotating at a speed of 25 r.p.m. The mixture was stirred for 10 minutes and it was then sieved thus obtaining a powder which was placed in a stainless steel cubical mixer of a capacity of 18 l and 0.85 Kg of spray-dried lactose, 0.45 Kg of Methocel® K100 and 0.45 Kg of Methocel® A4C (methylcellulose) were added. It was rotated at a speed of 25 r.p.m. for 10 minutes. 0.03 Kg of magnesium stearate previously sieved were added to the mixture and preparation of the tablets was carried out by compression of the mixture through rotating press. Dosage unit composition Trapidil 200 mg Methocel® K100 45 mg Methocel® A4C 45 mg Spray-dried lactose 85 mg Silica 2 mg Magnesium stearate 3 mg Tablet total weight 380 mg EXAMPLE 2 Preparation of tablets containing 200 mg of active principle with addition of citric acid. 2 Kg of Trapidil and 0.65 Kg of citric acid suitably ground and sieved were placed in a granulator-mixer and mixed for 10 minutes. Granulation of the mixture thus obtained was then carried out with H₂O. The granulate was dried in an air-circulation stove, sieved through a suitable sieve and then mixed with 0.45 Kg of Methocel® K100, 0.45 Kg of Methocel® A4C, 0.2 Kg of spray-dried lactose and 0.02 Kg of previously sieved silica, using a stainless steel cubical mixer of a 18 l capacity. It was stirred for 10 minutes at 25 r.p.m. 0.03 Kg of magnesium stearate previously sieved was added to the mixture and preparation of the tablets was carried out by compression of the mixture through a rotating press. Dosage unit composition Trapidil 200 mg Methocel® K100 45 mg Methocel® 4C 45 mg Spray-dried lactose 20 mg Silica 2 mg Magnesium stearate 3 mg Citric acid 65 mg Tablet total weight 380 mg In vitro release pattern of compositions prepared according to the Examples. Dissolution measurements were effected according to USP XXI method at 37°C and paddle speed of 50 r.p.m..The dissolution medium was simulated intestinal fluid at pH 6.8. Results of cumulative percentage release referred to the contents: Time (hours) Composition prepared according to example 1 Composition prepared according to example 2 (containing citric acid) 1 22.6 28.4 2 33.7 42.7 4 48.9 68.3 6 65.4 88.7 8 76.8 101.5 The above data show that the two formulations present a good in vitro release profile. The addition of citric acid brings a sensible increase of the release of the active principle. In vivo bioavailability tests Bioavailability and pharmacokinetic profiles of the pharmaceutical compositions described in examples 1 and 2, administered in unit doses containing 200 mg of Trapidil, were evaluated in 4 adult healthy volunteers, aged 20 to 50, of normal blood pressure and good physical conditions, avoiding the intake of other drugs. Each subject fasting, took each test composition, with an interval of 4 days between the two administration regimen and abstaining from food for 2 hours after each administration. Blood samples to determine concentration of the active principle were collected as follows: 30 minutes; 1 hour; 2 hour; 4 hour; 6 hour; 8 hour; 12 hour. The heparinized blood samples were centrifuged within 1 hour from sampling for 15 minutes at 1000xg and the separated plasma was kept under freezing at -18°C until the moment the active principle contents were assessed through HPLC technique by spectrophotometric detector. Table 1 shows the mean plasma concentrations time values expressed in µg/ml and the main pharmacokinetic parameters derived from plasma concentrations of both Trapidil and its main circulating metabolite. The results obtained with the compositions of examples 1 and 2 are compared with the results obtained in a different session, but under the same test conditions, with an equivalent dose of active principle administered in a composition at prompt release (2 tablets x 100 mg). The analysis of the results of the Trapidil plasma kinetics show that, following administration of sustained release compositions, a remarkable reduction of the peak plasma concentration and an extended absorption were produced, so that the resulting plasma levels mantain higher than 3 µg/ml after the fourth hour from administration. The advantages of the sustained release compositions of the invention are even more evident when comparing the cumulative data obtained by adding Trapidil plasma concentrations to the ones of its main metabolite. In fact, the controlled release of the active principle causes an equally gradual release of its metabolite in the blood to keep till the 12th hour hematic levels of the active components higher than 1 µg/ml, which is the lowest concentration threshold to produce a therapeutic effect. The pharmacokinetic profil of the composition of example 2, which contains citric acid in addition to other components, is even more favourable as: 1. after 1 hour from administration the Trapidil plasma values are higher than 3 µg/ml; 2. plasma levels of the active metabolite sensibly increase being superior or equal to 2 µg/ml until the 12th hour. The evaluation of the bioavailability of sustained release compositions in comparison to standard release ones, carried out by comparing the respective areas under the plasma concentration/time curves (AUC), calculated using the trapezoidal rule, indicates a loss of bioavailability, as it does frequently happens in the sustained release compositions. However, such bioavailability loss is limited to about 20% values. In a subsequent study carried out under conditions as previously described, it was also established that food does not influence the absorption of Trapidil from the compositions object of the invention. The drug can thus be taken in said formulations with no need for particular care. On the base of the results obtained following acute administration of standard and sustained release compositions of Trapidil, a simulation of plasma levels at the steady state was carried out, using a two compartments open model according to the procedure described in Notari R.E., Biopharmaceutics and Clinical Pharmacokinetics, III° ed., Marcel Dekker Inc. The results, shown in table 2, further prove that, while the conventional composition allows to keep the minimum concentration of 1 µg/ml of Trapidil and of its active metabolite at the most until the 6th hour after administration, the compositions of the invention (and in particular the acidified composition described in example 2) secure effective minimal hematic levels of the active components until the 12th hour. Cumulative simulated plasma levels of Trapidil and of its active metabolite (TP 1) in man at the steady state following oral administration of equivalent doses (300 mg/die) of prompt release composition and sustained release compositions of Trapidil prepared according to examples 1 and 2 of the invention. FORM TRAPIDIL AND TP1 PLASMA CONC.(µg/ml) AT VARIOUS TIMES (hours) basal 1 2 4 6 8 12 TRAPIDIL prompt release 0.62 3.56 3.14 1.79 1.06 0.62 TRAPIDIL composition of example 1 1.00 3.07 4.20 3.71 2.86 2.10 1.00 TRAPIDIL composition of example 2 1.66 4.19 4.90 4.85 3.88 2.96 1.66 The results confirm therefore the validity of the compositions of the invention, which ensure the presence in the organism of plasma concentrations of the drug and of its active metabolite sufficient to produce and keep the desired therapeutic effects by means of a simplified dosage scheme.

Claims: Claims for the following Contracting States : AT, BE, CH, DE, FR, GB, IT, LI, LU, NL, SE Sustained release pharmaceutical compositions for oral administration, containing Trapidil as the active principle, optionally an organic acid selected from tartaric, malic, maleic, malonic and citric acid and conventional excipients, in combination with a solid carrier material consisting of a mixture of hydroxypropylmethylcellulose, containing an average of 22.1% by weight of methoxy groups and an average of 8.1% by weight of hydroxypropoxy groups and whose viscosity degree is comprised between 10⁻² and 100 N s/m² (10 and 100,000 centipoises) with another cellulose ether, characterized in that the solid carrier material is in an amount comprised between 30% and 50% by weight of the active principle, with the proviso that the amount of said another cellulose ether is not less than 30% by weight of the mixture. Pharmaceutical compositions according to claim 1 wherein the solid carrier material consists of a mixture of hydroxypropylmethylcellulose and methylcellulose and citric acid. Pharmaceutical compositions according to claims 1-2, whose unit dosage form is a tablet containing an amount of active principle comprised between 100 and 300 mg. A process for the preparation of pharmaceutical compositions according to claims 1-3 consisting in the direct compression of a mixture of the active principle with 30-50% by weight with respect to the active principle of a solid carrier material consisting of a mixture of hydroxypropylmethylcellulose, an average of 22.1% by weight of methoxy groups and an average of 8.1% Or weight of hydroxypropoxy groups and whose viscosity degree is comprised between 10⁻² and 100 N s/m (10 and 100,000 centipoises) with another cellulose ether, wherein the amount of said another cellulose ether is not less than 30% by weight of said mixture, and with other conventional excipients, previous possible granulation of a mixture of the active principle with an organic acid selected from tartaric, malic, maleic, malonic and citric acid. A process according to claim 4 characterized in that a granulate of a mixture of the active principle with citric acid is prepared and that said granulate is subsequently mixed and compressed with the solid carrier material previously described. Claims for the following Contracting States : ES, GR A process for the preparation of sustained release pharmaceutical compositions for oral administration, containing Trapidil as the active principle in combination with a solid carrier material consisting of a mixture of hydroxypropylmethylcellulose containing an average of 22.1% by weight of methoxy groups and an average of 8.1% by weight of hydroxypropoxy groups and whose viscosity rate is comprised between 10⁻² and 100 Ns/m² (10 and 100,000 centipoises) with another cellulose ether in an amount not less than 30% by weight of said mixture, optionally in combination with an organic acid selected from tartaric, malic, maleic, malonic and citric acid, preferably citric acid, and with conventional excipients, which process consists in the direct compression of a mixture of the active principle with a solid carrier material consisting of a mixture of said hydroxypropylmethylcellulose with said another cellulose ether in an amount comprised between 30% and 50% by weight of the active principle, and with other conventional excipients, previous possible granulation of a mixture of the active principle with said organic acid. A process according to claim 1 characterized in that a granulate of a mixture of the active principle with citric acid is prepared and that said granulate is subsequently mixed and compressed with the solid carrier material previously described.

Inventors: ACERBI DANIELA, CHIESI PAOLO, PAVESI LUCIANA, ACERBI, DANIELA, CHIESI, PAOLO, PAVESI, LUCIANA
Applicants: CHIESI FARMA SPA, CHIESI FARMACEUTICI S.P.A.
Application year: 1988
Main classification: A61K9
IPC codes: A61P9, A61K31, A61K9, A61K47, A61P7