Method of Enhancing the Administration of Pharmalogically Active Agents

It is now a well established fact that a prerequisite for the action of a drug is its ability to penetrate the lipid cell membranes. A substance can act only through its undissociated, lipid soluble part. This sets a limitation for the intravenous administration of compounds with a pK.sub.a value far from the physiological pH range. On the other hand, a drug has to be dissolved in a physiological vehicle, which normally is an isotonic aqueous solution. Thus, many drugs can only be administered orally as tablets or as suspensions, despite the fact that there is a marked therapeutic need for a parenteral route of administration.

The degree of protein binding differs from drug to drug and from species to species. The albumin bound part of a drug may be regarded as a floating depot, but it has no pharmacological effect per se. Repeated administrations sooner or later give a saturation of the albumin binding capacity and finally enough free drug to give a pharmacological effect.

The physiological mechanism of the fat transport in the blood and lymph is by chylomicrons with a median particle diameter between 0.2 and 0.3 .mu.m (range 0.05 - 0.50 .mu.m) and containing phospholipids and protein in the membrane.

In the administration of pharmacologically active agents, it has up to now mostly been necessary to use water-soluble agents or to transform the agents into a water-soluble form, so that a solution can be obtained having the properties required for the administration. The use of the agents in a water-soluble form, however, has often had several disadvantages. For instance, the aqueous solutions may often be acidic or basic, which may cause side effects. Also, it may sometimes be difficult to attain a desired effect, as the solutions cannot be tolerated by the patient.

It has long been postulated that a higher degree of lipophilisity will support an increased pharmacological action of a pharmacon. In 1937 Meyer said that "Narcosis commences when any chemical indifferent substance has attained a certain molar concentration in the lipids of the cell." Until now, it has been difficult to deny or accept this theory as there was no way to administer these lipophilic and hydrophobic substances so that the pharmacokinetics of the compounds could not be investigated.

It is known from Remington's Pharmaceutical Sciences, 13th Edition, 1965, Page 228, Column 2, Line 23, that "Most stable emulsions have particle sizes in the range of 0.25 to 5.0 microns (.mu.)." However, the reference is to emulsions in general without any appreciation of the utilization of such emulsions for the parenteral administration of oil-soluble pharmacologically active agents, and more specifically there is no appreciation that such emulsions can be utilized as a carrier emulsion to enhance the parenteral administration of oil-soluble pharmacologically active agents whereby a lower dose rate can be utilized than heretofore to achieve a given effect.

U.S. Pat. No. 2,972,565 to Zilversmit discloses fat concentrates for use in the preparation of fat-in-water emulsions when diluted with water and disclosed as suitable for intravenous administration. However, we have made extensive tests in accordance with the examples of the Zilversmit patent, and all tests have ended in failure. Even with the use of modern high-speed emulsifying equipment, it has not been possible to prepare emulsions from Zilversmit's concentrates which have had the small and uniform particle size which is essential in accordance with the present invention. When administering placebo emulsions of this type to mice, up to 50% of the test animals have died. The teachings of the patent to Zilversmit cannot be considered to lead one skilled in the art to the present method of enhancing the parenteral administrations of oil-soluble pharmacologically active agents.

The present invention now refers to a new method of enhancing the administering of water-soluble pharmacologically active agents. According to the invention, a method of administering a pharmacologically active, oil soluble agent having a diagnostic or therapeutic effect is disclosed which comprises the steps of dispersing a pharmacologically acceptable lipoid in a pharmacologically acceptable aqueous solution to form an oil-in-water emulsion for stabilizing the dispersion of the lipoid in the form of particles substantially less than 4 microns in diameter, and generally of a mean particle size not over 1 micron, predominantly dissolving the active agent in the lipoid, and parenterally administering the emulsion with the active agent dissolved in the lipoid phase thereof. Through this method, an enhanced diagnostic or therapeutic effect is achieved with a rapid onset accompanied by a reduced incidence of injury to body tissues.

By the present invention, the disadvantages mentioned in the background of the invention can be avoided, as the active agents are administered dissolved or dispersed in a system of at least one finely dispersed hydrophobic component in at least one hydrophilic component, and primarily then in an emulsion or suspension of a pharmacologically inert fat or oil in an aqueous phase. Also, the agents may be used here without affecting the pH or the osmotic pressure of the aqueous phase, as the agent will mainly be present in a dissolved or dispersed state in the hydrophobic phase, and will not have any effect on pH or osmotic pressure. Because of this, the method of administration according to the invention will cause a lower occurrence of injuries to the body tissues. In most cases, the agent also gives a stronger effect and more rapid onset. Unexpectedly, this permits a smaller amount of the agent, i.e. a lower dose, to be used to achieve or maintain an effect that would otherwise require a significantly higher dose.

The aforementioned protein binding will also be reduced, as the agent is not in close contact with the proteins. A longer duration of the effect is also obtained in those cases where the agent normally is attacked rapidly by enzymes in metabolic processes. This is a very important characteristic of the present invention: a rapid onset and a good effect with a longer duration than for the water-soluble salt of the agent. It is a well known fact that the previous use of oil in injections has resulted in a slow release of the active agent from the site of injection in order to protect the patient from side effects due to overdosage. See U.S. Pat. No. 3,240,670 (column 1, line 17).

In the past, it has been the opinion of those skilled in the art that for parenteral injections, especially then intravenous injection, only aqueous systems could be used. See, for instance, "Husa's Pharmaceutical Dispensing", Mack Publishing Company, Easton, Pa. (1966). However, it has now been shown that provided the necessary precautions are taken, it is not only possible to use the new method of administration by parenteral injection, but even that superior results are attained. In view of the prior art, this is unexpected.

In the use of fat emulsions for intravenous nutrition, a possibility may also be stressed. In accordance with the invention, water-insoluble agents for therapeutic or diagnostic purposes may be administered to the patient simultaneously with the infusion of the fat emulsion.

It may occur that the active agent is not completely dissolved in the hydrophobic phase. It may have a greater affinity to the hydrophobic phase on account of its hydrophobic properties, but depending upon the distribution equilibria, both of the phases may contain the active agent. However, according to the most preferred embodiment, the agent is present predominantly as a fraction of the lipoid in the hydrophobic phase, in a dissolved state.

The method of the invention comprises most of the administration ways known in the medical art, but is especially intended for parenteral administration, preferably then intravenously, but also intramuscularly or subcutaneously. Examples of administration methods, other than those mentioned above, are the following:

Parenterally:

intradermally

intraarterially

intraspinally

intrathecally

intrapleurally

intraperitoneally

intrasynovially

The local administration mentioned above is not intended to refer to external local or topical administration, such as an unguent or cream, but rather to an internal local administration, such as directly in an operation wound and the like, where the emulsion with the active agent gets in a direct contact with the blood and lymph vessels.

The active agents with a therapeutic and/or diagnostic effect, which are to be used in the method of the invention, can be of very varying types, and the selection of these agents is only restricted by the conditions that they must be compatible with the vehicle system of several phases and that no harmful side effects may arise. In all cases an agent will be used which is soluble in the hydrophobic phase, such as an oil-soluble agent, but the agents may then also be partly soluble in the hydrophobic phase and be present in it with the other part as an emulsion or suspension on account of their greater affinity to this phase. It is also possible to administer simultaneously oil-soluble and water-soluble agents, each of these primarily being present in the phase to which they have the greatest affinity. However, that condition must always be satisfied that it must always be possible to combine the various components to a stable system with the desired properties, and no harmful side effects must arise.

At room temperature, the active agents are usually solids or liquids with a boiling point above 140.degree. C in order to avoid transport from the blood system through the capillaries in the lungs. They may also be lower boiling liquids, the salt form of which is solid. In any case, it is necessary that the agents are oil soluble.

Pharmacologically active agents which may be administered in accordance with the present invention, may be selected, but are not limited to the following groups:

Centrally and peripherally acting agents:

depressants

anaesthetics

analgetics

stimulants

spasmolytics

muscle relaxants

vasodepressants

In addition to the active agent or agents and the hydrophilic component, which consists of an aqueous solution, and the hydrophobic component, which consists of a pharmacologically inert lipoid, the compositions of the invention may contain other substances. These may for instance be preservatives, agents for pH adjustment, and agents for adjustment of the osmotic pressure. One of the most important additives will consist of one or more agents for achieving a stable dispersion of the hydrophobic phase in the hydrophilic phase. Many emulsifiers and suspension agents of a natural as well as synthetic origin may be used.

The preparations according to the method of the invention may contain from 1 up to 10 hydrophilic components, and usually they contain about 5 hydrophilic components.

As has been indicated above, the carrier or vehicle for the preparations according to the invention consists of a system of at least one hydrophobic component finely dispersed in at least one hydrophilic component. In most cases, the vehicle will consist of an emulsion or suspension of a fat or an oil in an aqueous solution, both phases of course being pharmacologically acceptable. For these certain conditions must be fulfilled. In a finely dispersed system which is to be introduced into the blood vessels, all the particles must have a diameter below 4 microns, as they will otherwise get stuck in the capillary vessels. A particle size of 1 micron or less is a salient aspect, and this also makes the system more stable. Moreover, the system must also be of such a type that the particles do not form aggregates. Furthermore, the vehicle system must also be able to withstand autoclaving and preferably also freezing, and it must have such a composition and such properties that it can be stored for a long time without physical and chemical breakdown. It is of course also an important requirement that the vehicle system itself must not cause undesirable effects.

In the vehicle systems most commonly used, which consists of an emulsion or suspension of a pharmacologically inert oil or fat in an aqueous solution, the hydrophobic component usually consists of a fat or an oil of vegetable or animal origin, such as soybean oil, cottonseed oil, coconut oil or olive oil. In order to obtain a stable system, it is furthermore necessary to include stabilizers of a natural or synthetic origin, such as phosphatides, polypropylene glycol, polyethylene glycol, polyglycerol monooleate, etc. The emulsions or suspensions used usually have a fat content of 0.1 - 99 per cent by weight, depending on the form of application. The amount of stabilizer in the compositions is determined by the properties of the system and depends on the nature of the dissolved active agent and usually lies between 0.1 and 20 weight per cent.

For the purposes of the invention, suitable fat emulsions have been prepared, and one example of such emulsions is described in the U.S. Pat. No. 3,169,094. This emulsion consists of soybean oil in water with native egg phosphatides added as a stabilizer, and it has proved to be free from harmful side effects also when administered in such large quantities as are required in intravenous fat nutrition. Other oils or fats and other stabilizers may also be used for the purposes of the invention, even if they give side effects when used for intravenous nutrition, as they are administered in much smaller quantities when used as vehicles for pharmaceutically active agents.

The invention is further illustrated by the following examples, which, however, are not limitative.

5 g of phenyramidol base is dissolved in 95 g of soybean oil. An emulsion is prepared of 20 g of such a soybean oil solution, 1 g of egg phosphatides, 2.5 of glycerol and 0.5 g of Myrj 52 (a registered trade mark for a nonionic emulsifier consisting of a polyoxyethylene derivative of fatty acids, from Atlas Co, described on page 709 of the Merck Index, 8th Ed., and on page 389 of the Extra Pharmacopoeia, Martindale, 26th Ed.), and sterile water to 100 ml. In the preparation, the conventional precautions for the preparation of bacteriologically acceptable injection solutions must be observed.

In pharmacological testing on mice, this composition shows a better effect than an aqueous solution of phenyramidol hydrochloride. Furthermore, the aqueous solution also has a lower pH value.

3.75 g hexobarbital

10 g soybean oil

25 g ethanol

1 g egg phosphatides

0.5 g Myrj 52 (same product as in Example 1)

Sterile water to 100 ml

An emulsion with the above composition is prepared in the same manner as in Example 1. In the finished emulsion, the majority of the particles have a size below 1 micron.

Mecamylamine (3-methylaminoisocamphane hydrochloride) is a ganglion-blocking secondary amine, and as a base, it is an oily liquid which is soluble in lipids. Its toxicity (LD.sub.50) after intravenous administration has been estimated in male albino mice of the NMRI strain in accordance with the method of the Nordic Pharmacopoeia. The following preparations were used:

Mecamylamine hydrochloride, 1% dissolved in saline

Mecamylamine base, dissolved in soybean oil and emulsified in the conventional way. Final concentration 1%.

Mecamylamine base, directly emulsified in 5.5% glucose solution with the aid of Pluronic F-68 (a registered trade mark for a nonionic emulsifier consisting of a block polymer of ethylene oxide and propylene oxide, from Wyandotte Chemical Corporation, described on page 392 of the Extra Pharmacopoeia, Martindale, 26th Edition) and an ultrasonic apparatus (20.000 Hz). Final concentration 1%.

The injections were given in the dorsal tail vein at a speed of 0.1 ml per 5 seconds. The results are listed in Table 1.

The intravenous toxicity of mecamylamine hydrochloride has earlier been found to be, by Stone et al.: 21.0 mg/kg Stone, C. A., Torchiana, M. L., Navarro, A. and Beyer, K. H.: "Ganglionic blocking properties of 2-methylaminoisocamphane hydrochloride (Mecamylamine), a secondary amine", J. Pharmacol. Exptl. Therap.: 169-183 (1956)! and by Corne & Edge: 12.9 mg/kg Corne, S. J. and Edge, N. D.: "Pharmacological properties of pempidine (1,2,2,6,6-pentamethylpiperidine, a new ganglio-blocking compound", Brit. J. Pharmacol.: 13: 339-349 (1958)!, which statistically does not differ from the above results.

All the quantal log-dose-response lines had the same slope and a comparison between the hydrochloride and the two emulsions showed a slight increase in toxicity for the pure base preparation, 138% (125-150%), but no difference for the soybean oil preparation, 106% (99-113%), the fiducial limits given at P = 0.05.

As can be seen from the table, there was no difference in survival time (the time from the injections to death) between the preparations.

To summarize, it can be stated that the toxic effects of mecamylamine have not been altered to any notable degree by the different galenic modifications used.

The question to be considered here is the influence of protein binding on a drug, which is dissolved in the oil phase of an emulsion. Quinidine is bound to plasma albumin to an extent of about 80%, and the therapeutic use of its water soluble salts by intravenous injection may therefore be hazardous. The individual rate and speed of albumin binding seems to be more important than the magnitude of the dose given.

A male mongrel dog with an irregular heart rate, between 60 and 130 beats per minute, was anaesthesized with urethane, and blood pressure, ventilation, heart rate and ECG were recorded.

Quinidine base, dissolved in soybean oil suspended in water with a final concentration of 0.3% was injected into the femoral vein (1 mg/kg). A few seconds after the injection was finished, the heart rate was regulated, and this effect persisted for about 30 minutes.

When a placebo emulsion was administered, no effect could be registered, but when the quinidine injection was repeated, there was again a regulation, which persisted for about one hour.

These results have been followed up in strophantine induced arrythmias in dogs, and it is found that quinidine base dissolved in oil and emulsified in water is a better and safer preparation for intravenous injections than aqueous solutions of the quinidine salts.

The emulsion has an instant action when administered intravenously.

Rats: At a dose of 60 mg/kg, the animals fall asleep without excitation. A constant supply of 35 mg/kg gives continuous sleep and after interruption of the infusion, the animals wake up after about 3 min.

Cats: The effects of the emulsion on the blood pressure when given intravenously in a dose of 5-10 mg/kg was registered on a chloralose-anaesthetized cat. The emulsion and a solution of sodium hexobarbital both gave a depression of about 60 mm Hg with about the same duration.

Mouse: The sleeping time after a single dose injection of the emulsion was shorter than the sleeping time after injection of an aqueous solution of sodium hexobarbital:

In accordance with common practice, the sleeping time has been set as the duration of the loss of the righting reflex.

In rats, an instant sleeping effect was obtained.

In rabbits, 80 mg/kg, administered intravenously slowly (5 minutes) gives a light sleep with an onset time of 30 seconds and a duration of 9 minutes. The awakening was without remarks.

The following preparations have also been prepared and administered by parenteral injection with good results:

Cyclandelate (3,5,5-trimethylcyclohexyl mandelate) which is almost completely insoluble in water has been administered intraarterially in the hind leg of cats anaesthetized with chloralose, and in doses of about 1-2 mg/kg body weight, causing a marked vasodilation within a few seconds, especially in noradrenaline induced vasoconstriction. The systemic effect (heart rate, blood pressure, etc.) on the circulation of the cats was negligible within the dose range used. It has not been possible earlier to demonstrate this marked local vasodilating effect, as it has not been possible earlier to administer cyclandelate by injection.

"Myvacet 9-40" is a registered trade mark for acetylated monoglycerides, sold by Distillation Products Co.

In this example, the acute toxicity (LD.sub.50) and the anticonvulsant activity of various diazepam formulations has been investigated in mice. In accordance with the invention, a diazepam emulsion was prepared with the followng composition:

This formulation was compared to a commercial diazepam formulation for injection, which is sold under the registered trade mark Valium from Hoffman La Roche & Co. This commercial diazepam formulation contains 5 mg/ml of diazepam dissolved in an aqueous mixture containing 41.4% propylene glycol, 8.06% ethanol, 1.57% benzyl alcohol, 0.12% benzoic acid and 4.88% sodium benzoate. It is necessary to use this mixture, as diazepam is not soluble in water alone.

The test results showed that the two formulations had nearly equal anticonvulsant activities, but that the diazepam formulation of the invention had an LD.sub.50 of 283.3 mg/kg, while the LD.sub.50 of the commercial diazepam formulation was 83.4 mg/kg. It is believed that the solvents necessary in the commercial diazepam formulation contribute in a large degree to its greater toxicity, and this has been confirmed in a test with a placebo solution using only the solvents of the commercial diazepam formulation. This placebo solution had an LD.sub.50 of 90.5 mg/kg.

Thus, it has been shown that the administration in accordance with the invention can be made much safer than in prior methods.

This example shows how the incidence of injuries in the form of thrombophlebitis is drastically reduced through the present invention. Thrombophlebites are inflammations in the venous walls, and they can sometimes have quite serious consequences. At intravenous injections, however, they have been such a common occurrence and their appearance has sometimes not even been noted, but they have been considered as an unavoidable evil. In the use of barbiturates for intravenous anaesthesia, the rate of thrombophlebitis within two weeks after injection has been found to be from 10 to 30 percent.

In a comparative test, a commercial 5.5% water solution of Narkotal, trade mark for pronarcon or 5-(2-bromoallyl)-5-isopropyl-1-methylbarbituric acid, was administered intravenously to 53 patients. It was found that within a week, 16 of the patients, i.e. 30%, developed symptoms of thrombophlebitis. In another test, an emulsion prepared in accordance with the invention and containing 1.5 percent secobarbital in the oil phase was administered intravenously in the same way to 62 patients. It was found that none of these patients developed any thrombophlebitis symptoms. This clearly shows that the risk of injuries to the tissues is markedly decreased in the method of the invention.

This example shows that it is preferred that the active agent used has a boiling point above 140.degree. C.

An emulsion composition was prepared containing 5 percent of methoxyflurane (2,2-dichloro-1,1-difluoroethyl methyl ether; b.p. 105.degree. C) in a carrier system of soybean oil emulsified in water with the help of egg phosphatides. This formulation was administered to mice, and the LD.sub.50 value was found to be 150.4 mg/kg.

It was not possible to establish a relation between the sleeping time and the administered dose. Within a dose range from 118 to 190 mg/kg, the surviving animals slept from 0.6 to 2.0 minutes. There was, however, no correlation between the magnitude of the dose and the sleeping time, and therefore, this cannot be considered as a genuine effect. The reason for this is that the methoxyflurane was eliminated through the respiratory tract so quickly that the pharmacological effect was not obtained.

As discussed, a salient aspect of the invention resides in the fact that the mean particle size of the lipid particles comprising the inner phase of the carrier emulsion utilized in carrying forth the present method is preferably not over 1 mm. To facilitate the practice of the present invention the following method is discussed as being suitable for the predetermination of the particle size distribution.

A convenient method to determine the size distribution pattern in particulate formulations has been published by Groves, Yalabik and Tempel Powder Technology 11, 245 - 255, 1975. It's application in lipid emulsion formulations was described by Groves and Yalabik Powder Technology, presently in press. The method uses a laser beam and photodetector as the sensing system for the lipid particles in a centrifugal field and the size distribution is calculated by using the centrifugal analogue of Stokes' law.

The laser photosedimentometer was used to determine the particle size distribution of seven different emulsions of types according to the present invention. The factor d.sub.st(50) (Stokes' diameter) is calculated in the particle size determinations. This value indicates the mean diameter (at 50%) and the width of the distribution is expressed by the slope (standard deviation) in Table II.

While it is believed that the unexpected result obtained by the practice of the method of the present invention is apparent from the foregoing specific Examples, particular attention is directed to, for instance, the enhanced administration of the pharmacological agents diazepam and barbituates, see Examples 17 and 18 respectively.

From a consideration of Example 17 it will be seen that the acute toxicity of diazepam when administered parenterally in accordance with the present invention is substantially lower than than of diazepam administered by a prior parenteral method. In Example 18 it will be seen that the use of barbituates for intravenous anaesthesia administered parenterally in accordance with the present method resulted in a marked decrease of risk of injury to tissues, namely inflammation of the venous walls thereby greatly enhancing the administration of barbituates for intravenous anaesthesia.