Method of enhancing absorptions of transmucosal administration formulations

Abstract

Disclosed is a method for enhancing absorption of a medicament that is suitable for administering transmucosally to a subject by providing an environment of the administration with a suitable pH. A medicament of propranolol suitably administered sublingually is provided. The medicament of propranolol can be used for treating cardiovascular diseases.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed to a method for enhancing absorption of a medicament that is suitable for transmucosal administration, particularly to a method for enhancing absorption of a medicament suitable for sublingual administration.

2. Description of the Related Art

Transmucosal drug delivery system has been studied for years because it can avoid the liver first-pass effect. The study on this field focuses on how to enhance absorption of the drug. General approaches reported to enhance absorption include the use of various permeation enhancers such as bile salts, surfactants, organic solvents, chelating agents as well as salicylate and Azone®.

Factors affecting the permeation of a drug via oral mucosa, such as sublingual mucosa, include solubility of the drug, partition coefficient, degree of ionization of the drug, and molecular size and weight of the drug. For a given drug, the molecular size and weight are fixed and cannot be changed. Changes in solubility and degree of ionization will influence partition coefficient and permeability. Therefore, optimization of combined solubility and ionization are variable factors to achieving maximum rate and extent of absorption through oral mucosa such as sublingual mucosa.

SUMMARY OF THE INVENTION

A first aspect of the preferred embodiments provides a method for enhancing absorption of a medicament that is suitable for administering transmucosally, such as sublingually in a subject. The medicament used in the preferred embodiments includes a therapeutically effective amount of an active compound or a pharmaceutically acceptable form thereof, or a combination thereof and a pharmaceutically acceptable carrier.

The inventors have found that maximum flux of ionized and non-ionized forms of an active compound of a medicament across the mucosal membrane can be achieved with the attainment of a pH in a mucosal medium by involving certain amount of buffering agents with the medicament. The method of the preferred embodiments comprises providing an environment for the administration with a pH of about: $\begin{array}{cc}\mathrm{pH}=-\log \left(\frac{\mathrm{Ka}·S_i}{S_u}\right)& \left(I\right)\end{array}$
in which K_a is the ionization constant (dissociation constant) of the active compound in water, S_i is the solubility of the ionized form of the compound, and S_u is the solubility of the non-ionized form of the compound.

A second aspect of the preferred embodiments is to provide a method for enhancing absorption of a medicament comprising propranolol or a pharmaceutically acceptable form thereof that is administered transmucosally to a subject, comprising providing an environment of the administration with a pH range of about 7.2 to about 7.8.

A third aspect of the preferred embodiments is to provide a medicament suitable for a transmucosal administration to a subject, comprising an effective amount of propranolol or a pharmaceutically acceptable form thereof, and a pharmaceutically acceptable carrier, in which the medicament provides an environment of the administration with a pH range of about 7.2 to about 7.8.

A fourth aspect of the preferred embodiments is to provide a method for treating cardiovascular diseases of a subject comprising transmucosally administering a therapeutically effective amount of propranolol or a pharmaceutically acceptable form thereof to the subject in an environment with a pH range of about 7.2 to about 7.8.

Compared to a conventional formulation of propranolol, the formulation of the preferred embodiments can significantly decrease the heart rate in a subject in a very short time, and can be used to treat cardiovascular related diseases (urgent medical conditions) such as atrial fibrillation with rapid heart rate, panic attacks with rapid heart rate, acute hypertension, headache and angina.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows heart rates of two healthy subjects after sublingually administering propranolol powder in various pH values; and

FIG. 2 shows a change of heart rate after administered with equivalent sublingual dose of a buffered propranolol tablet of the preferred embodiments versus a conventional Inderal tablet in 2 healthy subjects.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As stated above, the preferred embodiments provide a method for enhancing absorption of a medicament that is suitably administrated transmucosally. In one embodiment, the medicament is administered sublingually by adjusting the pH of the environment of administration of the medicament. We found that an active compound of a medicament can be significantly absorbed when an environment of the administration of the medicament is kept around: $\begin{array}{cc}{\mathrm{pH}}_{\max }=-\log \left(\frac{\mathrm{Ka}·S_i}{S_u}\right)& \left(I\right)\end{array}$
in which K_a is the ionization constant (dissociation constant) of the active compound of the medicament in water, S_i is the solubility of the ionized form of the compound, and S_u is the solubility of the non-ionized form of the compound. S_i and S_u can be easily obtained by measuring the drug solubility at two extreme pH levels where the ionized or non-ionized species are dominating.

Theoretically, an ionizable medicament to transport across the mucosa includes both the ionized form and the non-ionized form of the medicament. The overall steady-state flux (J_ss) and the apparent permeability coefficient (P_app) of a medicament across the mucosa are the summations of the individual contribution from both the ionized and the non-ionized forms. Therefore, the J_ss and P_app of such a medicament permeate across the mucosa can be expressed by the following equations: $\begin{array}{cc}{J}_{\mathrm{ss}\left(u\right)}=\frac{d{Q}_u}{dt·A}=P_u{C}_u& \left(1\right)\\ J_{\mathrm{ss}\left(i\right)}=\frac{d{Q}_i}{dt·A}=P_i{C}_i& \left(2\right)\\ J_{\mathrm{ss}}=J_{\mathrm{ss}\left(u\right)}+J_{\mathrm{ss}\left(i\right)}& \left(3\right)\\ P_{\mathrm{app}}=P_i{X}_i+P_u{X}_u& \left(4\right)\\ C_0=C_i+C_u& \left(5\right)\end{array}$

In the above equations, J_ss(u) and J_ss(i) are the steady-state flux of the ionized form and the non-ionized form of the medicament, respectively; Q_u and Q_i are the accumulated amount of the ionized form and the non-ionized form of the medicament penetrated across the mucosa, respectively; A is the surface area of the mucosa; C₀ is the loading concentration of the medicament; P_i and P_u are the permeability coefficient of the ionized form and the non-ionized form, respectively; X_i and X_u are the fraction of the ionized form and the non-ionized form, respectively; and C_i and C_u are the concentration of the ionized and non-ionized forms, respectively. Unlike J_ss(u) and J_ss(i), P_i and P_u are all independent of pH of the solution (environment). Therefore, we would expect that maximal C_i and C_u will be reached at an optimal pH_max, which will be the solubility of the ionized form (S_i) and the non-ionized form (S_u), respectively, and the maximal steady-state flux can be obtained accordingly. $\begin{array}{cc}{\left(J_{\mathrm{ss}}\right)}_{\max }=P_i{S}_i+P_u{S}_u& \left(6\right)\\ W\mathrm{hen}\mathrm{pH}\le {\mathrm{pH}}_{\max },J_{\mathrm{ss}}=P_i{S}_i+P_u{S}_i\frac{K_a}{\left[H^{+}\right]}& \left(7\right)\\ W\mathrm{hen}\mathrm{pH}>{\mathrm{pH}}_{\max },J_{\mathrm{ss}}=P_u{S}_u+P_i{S}_u\frac{\left[H^{+}\right]}{K_a}& \left(8\right)\end{array}$

It is expected that the best flux of the medicament across the mucosa would be achieved if we could achieve the pH_max in the environment a certain amount of buffering agents in a specific formulation of the medicament.

As used herein, the term “absorption”, unless specified otherwise, means “penetration” of the active compound of the medicament through the mucosa.

The term “transmucosal”, unless specified otherwise, means any route of the administration via the mucosal membrane. Examples include, but are not limited to, sublingual, nasal, vaginal and rectal. In the preferred embodiments, the administration is preferably performed sublingually.

The term “environment” or “environment of an administration” means an environment where an active compound of a medicament is absorbed by permeation across the mucosa. For example, when the administration is performed sublingually, the environment is saliva, which contains the drug and is “bathing” the sublingual mucosal membrane.

The term “subject” means animals and human. Human is preferable in the preferred embodiments.

The method of the preferred embodiments which provides an environment with a certain pH includes providing the environment with a preferable pH during the administration of the medicament, and making a suitable formulation of the medicament in such a way that the medicament itself can provide the environment with a desired pH. In the preferred embodiments, the latter is preferably. In this case, buffering agents are preferably involved in the formulation.

Buffering agents that can be used in the preferred embodiments will be obvious for those skilled in the art. Please see “Handbooks Pharmaceutical Excipients (Second Edition), edited by Ainley Wade and Paul J W Weller, The Pharmaceutical Press London, 1994”, which is incorporated herein by reference. Exemplified buffering agents include, but are not limited to, phosphates, such as sodium phosphate; phosphates monobasic, such as sodium dihydrogen phosphate and potassium dihydrogen phosphate; phosphates dibasic, such as disodium hydrogen phosphate and dipotassium hydrogen phosphate; citrates, such as sodium citrate (anhydrous or dehydrate); bicarbonates, such as sodium bicarbonate and potassium bicarbonate. The amount of buffering agents used in the medicament is readily determined by those skilled in the art, which depend on preferable pH values.

The medicaments of the preferred embodiments can include various formulations dependent on the dosage forms or formulations of administration. For example, if the medicament is administered sublingually, it can be in the form of tablets, pills, pellets, powders or sprays. Examples of other suitable formulations include, but are not limited to, ointments, capsules, solutions, syrups, drops, granules and suppositories. In any formulation, the medicament can include a therapeutically effective amount of an active compound or a pharmaceutically acceptable form thereof or either entity and a pharmaceutically acceptable carrier. Examples of the active compounds include, but are not limited to, propranolol, scopolamine, and estradiol. In the preferred embodiments, propranolol is preferable.

The carrier suitably used in the preferred embodiments depends on the specific formulation of the medicament, which is known by those skilled in the art. The carriers include, without limitation, fillers, binders, lubricants, diluents, sweetening and flavoring agents, preservatives, disintegrators, grilling agents, permeation enhancers. Examples of the carriers include starch, gelatin, natural sugars, corn, natural and synthetic gums such as acacia, sodium alginate, methylcellulose, carboxymethylcellulose, polyethylene glycol, waxes, boric acid, sodium benzoate, sodium acetate, sodium chloride, agar, bentonite, agar gum, stearates such as sodium stearate, HPMC, and palmitic acid, dimethyl sulfoxide, N,N-dimethyl acetamide, N,N-dimethylformamide, 2-pyrrolidone, 1-methyl-2-pyrrolidone, 1,5-dimethyl-2-pyrrolidone, 1-ethyl-2-pyrrolidone, 2-pyrrolidone-5-carboxylic acid, N,N-dimethyl-m-toluamide, urea, ethyl acetate, 1-dodecylazacycloheptan-2-one (Azone®), oleic acid, ethylene vinylacetate copolymer, polyvincyl chloride, polyethylene, polydiethyl phthalate.

Medicaments suitably used in the preferred embodiments are those suitably administered transmucosally which are well known by one skilled in the art.

Propranolol, 1-(isopropylamino)-3-(1-naphthyloxy)-2-propanol, a nonselective β₁ and β₂-adrenergic antagonist, has been widely used in the treatment of various cardiovascular diseases such as essential arterial hypertension, ischemic heart disease and atrial fibrillation. At present, injection and oral tablet are the only two dosage forms marketed commercially. Intravenous or intramuscular administration of propranolol can achieve fast onset of action. However, they are inconvenient and not suitable for self-medication.

Though oral administration of propranolol tablets has proven to be safe and effective in the treatment of atrial fibrillation, its onset of action is usually over 1 hr. Also, due to extensive hepatic first-pass effect, it has a short plasma half-life (2.8-4.4 hr), and a low bioavailability (10-30%).

To overcome these drawbacks, the preferred embodiments provide a method for enhancing the absorption of a medicament comprising propranolol or a pharmaceutically acceptable form thereof that is administered transmucosally in a subject, comprising providing an environment for the administration with a pH range of about 7.2 to about 7.8; and a medicament of propranolol that is suitably administered sublingually to a subject. The medicament propranolol of the preferred embodiments comprises an effective amount of propranolol or a pharmaceutically acceptable form thereof, and a pharmaceutically acceptable carrier, provided that the medicament provides an environment of the administration with a pH range of about 7.2 to about 7.8.

In the preferred embodiments, the medicament contains an effective amount of propranolol or a pharmaceutically acceptable form thereof, and a pharmaceutically acceptable carrier as described above, which can be formulated as a tablet, pill, pellet, spray, or powder, preferably as a tablet for sublingual administration. In the formulation, active compound propranolol can be used in the form of any pharmaceutically acceptable form such as free base, acidic salts, hydrates thereof, and acidic salts of the hydrates. In the preferred embodiments, the acidic salt form of propranolol is preferable because propranolol is a weak base. The acidic salts include, but are not limited to, a salt with inorganic acids such as hydrochloride, sulfate, and phosphate; and a salt with organic acids such as maleate, benzsulfonate acid, and citrate.

It has been investigated that permeability across the sublingual mucosa is dependent on the concentration of non-ionized propranolol in the environment. When a formulation of propranolol provides saliva with pH of about 7.2 to about 7.8, propranolol should maintain relatively high solubility as well as high fraction of non-ionized form in the saliva of human oral cavity. Preferably, the formulation for sublingual delivery is at about pH 7.6. This can be confirmed by equation (I). For propranolol: S_i is 22.118 (mg/ml), S_u is 0.539 (mg/ml) and K_a is 10^−9.23. $\mathrm{pH}=-\log \left(\frac{{10}^{-9.23}\times 22.118}{0.539}\right)=7.62$

To achieve this, buffering agents chosen include sodium bicarbonate, sodium phosphate, or a combination of borates and sodium hydroxide. Preferable examples include buffering agents Na₂HPO₄, Na₂HPO₄—NaH₂PO₄, Na₂HPO₄-citric acid, and Tris-HCl. Specifically, disodium hydrogen phosphate, by weight of about 10-25%, was found to effectively control the pH of saliva to be about 7.2 to about 7.8.

The medicament of propranolol of the preferred embodiments comprises an effective amount of an active component, and a suitable carrier. The term of “effective amount” means about 0.01 to about 99.99% in the formulation by weight. Preferably, the active compound propranolol accounts for about 1-90% in the formulation by weight. More preferably, the active component accounts for about 2-50% in the formulation by weight, and most preferably, about 5-10% in the formulation by weight.

The amount of the active component mentioned in the preferred embodiments, unless specified otherwise, means the amount of free compound of propranolol. The formulation of the preferred embodiments can be prepared to contain an amount of propranolol as those commercially available such as about 10 mg, 20 mg, 40 mg, or 80 mg in a tablet. It is also suitable that the formation may contain propranolol in an amount less than that commercially available, when it is used for urgent situations. Those skilled in the art will readily determine a suitable amount of propranolol in a specific formulation suitable for a given patient.

EXAMPLE 1

Ingredients Weight (g)

Ingredients                 Weight (g)
Propranolol hydrochloride   40
Disodium hydrogen phosphate 40
Lactose monohydrate         109
HPMC                        20
Magnesium stearate          2

Propranolol powder was mixed with magnesium stearate. To the resulting mixture was added other components, and then commingled in a V-blender for 15 minutes. The thoroughly blended composition was compressed into 1,000 plain tablets, each with 5 mm in diameter and 2-3 mm in thickness.

EXAMPLE 2

Ingredients Weight (g)

Ingredients                 Weight (g)
Propranolol                 20
Sodium dihydrogen phosphate 40
Lactose                     129
HPMC                        20
Magnesium stearate          2

All ingredients were formed as 1,000 tablets in the same way as in Example 1.

EXAMPLE 3

Ingredients Weight (g)

Ingredients                 Weight (g)
Propranolol                 20
Sodium dihydrogen phosphate 1.5
Disodium hydrogen phosphate 38.5
Lactose monohydrate         109
HPMC                        20
Magnesium stearate          2

All ingredients were formed as 1,000 tablets in the same way as in Example 1.

Experiment 1

Pharmacodynamic Investigations

I. Methods and Materials

Two healthy male subjects took part in the preliminary pharmacodynamic investigation of sublingual administration of buffered propranolol powder with 4 different buffering capacities as shown in Table 1.

TABLE 1
	Dosage	Propranolol		Saliva pH	Disappeared
Formulations	Forms	(mg)	Buffering Agent	(Mean)	(% Mean)
1	Powder	20	0		7.13	45.64
2	Powder	20	38.2	mg Na2HPO4 and	7.37	48.34
			1.8	mg NaH2PO4
3	Powder	20	40	mg Na2HPO4	7.64	55.56
4	Powder	20	20	mg NaHCO3	7.88	44.35

The subjects had not taken any sublingual medicine 2 weeks prior to and during the period of the study. Alcohol and smoking were not permitted for 24 hr prior to, and for the duration of the study. Caffeine-containing products were also not allowed from 8 hr prior to, and during, each study period.

The subjects were placed in a seated position for about 30 min prior to baseline measurements being made. A Dinamap BP monitor (Wipro GE Co., USA) was used to record systolic, diastolic, and mean blood pressure and heart rate every minute for 10 minutes before administration of sublingual propranolol. After sublingual administration, each subject was refrained from swallowing any propranolol or saliva until about 25 minutes, then the saliva was spit out and collected for pH measurement. Subsequently the mouth was rinsed 4 times with pure water. Pharmacodynamic parameters such as heart rate and blood pressure were measured. The heart rate change is shown in FIG. 1 and results reported as mean±SD. The blood pressure changes were variable and no significant hypotension occurred.

II. Results

The reduction of heart rate was highly dependent on the pH of saliva achieved from various buffering agents in the formulations (FIG. 1). Subjects receiving formulation 3 showed a drop of more than 10% of heart rate following 10 minutes of administration of sublingual propranolol, which is much faster onset of action than other formulation with different saliva pH.

Moreover, the maximal reduction of heart rate was 17% for formulation 3, whereas only 5-10% maximal reductions were found for the other 3 formulations. These results indicated that formulation 3 could effectively enhance the sublingual absorption of propranolol and rapidly reduce the heart rate in comparison to other 3 formulations.

Experiment 2

Control Test

I. Materials

Propranolol hydrochloride was ordered from Chang Zhou Guangming Biochemical Laboratories (BP 2000/USP24). Disodium hydrogen phosphate and HPMC (50 cps) were supplied by Sigma-Aldrich Co. (St. Louis, Mo., USA). Lactose monohydrate was supplied by Fisher Scientific UK Ltd. (Leicestershire, UK). Magnesium stearate was obtained form Wing Hing (Hong Kong).

Inderal 40 mg propranolol tablets were purchased from AstraZeneca UK Ltd. (Macclesfield Cheshire, UK).

II. Methods

Two healthy male subjects took part in the preliminary pharmacodynamic investigation once with buffered sublingual propranolol tablets as prepared in Example 1 and the Inderal tablet, respectively. The procedure of this study was similar to that described in Experiment 1 except that following the tablet, and the saliva was spit out in 8 minutes.

III. Results

The saliva pH of the Inderal tablet and that of the buffered tablet of the preferred embodiments were shown in Table 2. These results were shown in FIG. 2. The results showed that the buffered formulation quickly reduced 8% heart rate after 10 min of sublingual administration. However, the effect of the Inderal tablet was delayed to over 15 minutes and only a 6% reduction of heart rate. The heart rate continued to decrease with both the formulations, reaching a maximum effect around 20 minutes. The mean maximum effect of the buffered propranolol tablet was about 12% reduction whereas the Inderal tablet only about 7% reduction. The effect on the blood pressure was variable following both the formulations and no significant hypotension was observed.

TABLE 2
                Saliva pH
Dosage forms    (Mean ± SD) (n = 2)
Inderal tablet  6.82 ± 0.10
Buffered tablet 7.52 ± 0.05

Many modifications and variations of the embodiments described herein may be made without departing from the scope, as is apparent to those skilled in the art. The specific embodiments described herein are offered by way of example only.

Claims

1. A method for enhancing absorption of a medicament that is suitable for transmucosal administration to a subject, said method comprising providing an environment for the administration with a pH of about: pH = - log ⁡ ( Ka · S i S u )

in which Ka is the ionization constant (dissociation constant) of the compound in water, Si is the solubility of the ionized form of the compound, and Su is the solubility of the non-ionized form of the compound.

2. The method of claim 1, wherein the pH of the environment is provided by a buffering agent in the medicament.

3. The method of claim 2, wherein the environment of administration is in the oral mucosa.

4. The method of claim 3, wherein the environment of administration is a sublingual environment.

5. The method of claim 1, wherein the medicament is propanolol.

6. The method of claim 1, wherein the medicament is selected from the group consisting of scopolamine and estradiol.

7. A method for enhancing absorption of a medicament comprising propranolol or a pharmaceutically acceptable form thereof that is administered transmucosally to a subject, comprising providing an environment for the administration with a pH in the range from about 7.2 to about 7.8.

8. The method of claim 7, wherein the medicament is administered sublingually.

9. The method of claim 8, wherein the pH is about 7.6.

10. The method of claim 8, wherein the pharmaceutically acceptable form is an acidic salt.

11. The method of claim 10, wherein the salt is hydrochloride.

12. The method of claim 8, wherein the medicament comprises a buffering agent.

13. The method of claim 12, wherein the buffering agent is a phosphate buffer.

14. The method of claim 13, wherein the buffering agent is disodium hydrogen phosphate, sodium dihydrogen phosphate or a combination thereof.

15. A medicament suitable for transmucosal administration to a subject, comprising an effective amount of propranolol or a pharmaceutically acceptable form thereof, and a pharmaceutically acceptable carrier, wherein the medicament provides an environment of the administration with a pH of about 7.2 to about 7.8.

16. The medicament of claim 15, wherein the pH is from about 7.6.

17. The medicament of claim 15, wherein the pharmaceutically acceptable form is a salt.

18. The medicament of claim 17, wherein the salt is hydrochloride.

19. The medicament of claim 15, wherein the medicament comprises a buffering agent.

20. The medicament of claim 19, wherein the buffering agent is a phosphate buffer.

21. The medicament of claim 20, wherein the buffering agent is disodium hydrogen phosphate, sodium dihydrogen phosphate or a combination thereof.

22. The medicament of claim 15, wherein the medicament is formulated as a tablet.

23. The medicament of claim 22, wherein the tablet contains propranolol of from about 20 mg to about 80 mg.

24. A method for treating cardiovascular diseases of a subject comprising transmucosal administration of a therapeutically effective amount of propanolol to the subject in an environment with a pH range of about 7.2 to about 7.8.

25. The method of claim 24, wherein the administration is performed sublingually, and the pH is about 7.6.