Color Atlas of Pharmacology (Part 2): Drug Administration

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Drug Administration be very precise. (Standardized medicinal teaspoons and tablespoons are available.) Eye drops and nose drops (A) are designed for application to the mucosal surfaces of the eye (conjunctival sac) and nasal cavity, respectively. In order to prolong contact time, nasal drops are formulated as solutions of increased viscosity. Solid dosage forms include tablets, coated tablets, and capsules (B). Tablets have a disk-like shape, produced by mechanical compression of active substance, filler (e.g., lactose, calcium sulfate), binder, and auxiliary material (excipients). The filler provides bulk enough to make the tablet easy to handle and swallow. It is important to...

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8 Drug Administration Dosage Forms for Oral, Ocular, and be very precise. (Standardized medici- Nasal Applications nal teaspoons and tablespoons are available.) A medicinal agent becomes a medica- Eye drops and nose drops (A) are tion only after formulation suitable for designed for application to the mucosal therapeutic use (i.e., in an appropriate surfaces of the eye (conjunctival sac) dosage form). The dosage form takes and nasal cavity, respectively. In order into account the intended mode of use to prolong contact time, nasal drops are and also ensures ease of handling (e.g., formulated as solutions of increased stability, precision of dosing) by pa- viscosity. tients and physicians. Pharmaceutical Solid dosage forms include tab- technology is concerned with the design lets, coated tablets, and capsules (B). of suitable product formulations and Tablets have a disk-like shape, pro- quality control. duced by mechanical compression of Liquid preparations (A) may take active substance, filler (e.g., lactose, cal- the form of solutions, suspensions (a cium sulfate), binder, and auxiliary ma- sol or mixture consisting of small wa- terial (excipients). The filler provides ter-insoluble solid drug particles dis- bulk enough to make the tablet easy to persed in water), or emulsions (disper- handle and swallow. It is important to sion of minute droplets of a liquid agent consider that the individual dose of or a drug solution in another fluid, e.g., many drugs lies in the range of a few oil in water). Since storage will cause milligrams or less. In order to convey sedimentation of suspensions and sep- the idea of a 10-mg weight, two squares aration of emulsions, solutions are gen- are marked below, the paper mass of erally preferred. In the case of poorly each weighing 10 mg. Disintegration of watersoluble substances, solution is of- the tablet can be hastened by the use of ten accomplished by adding ethanol (or dried starch, which swells on contact other solvents); thus, there are both with water, or of NaHCO3, which releas- aqueous and alcoholic solutions. These es CO2 gas on contact with gastric acid. solutions are made available to patients Auxiliary materials are important with in specially designed drop bottles, ena- regard to tablet production, shelf life, bling single doses to be measured ex- palatability, and identifiability (color). actly in terms of a defined number of Effervescent tablets (compressed drops, the size of which depends on the effervescent powders) do not represent area of the drip opening at the bottle a solid dosage form, because they are mouth and on the viscosity and surface dissolved in water immediately prior to tension of the solution. The advantage ingestion and are, thus, actually, liquid of a drop solution is that the dose, that preparations. is, the number of drops, can be precise- ly adjusted to the patient‘s need. Its dis- advantage lies in the difficulty that some patients, disabled by disease or age, will experience in measuring a pre- scribed number of drops. When the drugs are dissolved in a larger volume — as in the case of syrups or mixtures — the single dose is meas- ured with a measuring spoon. Dosing may also be done with the aid of a tablespoon or teaspoon (approx. 15 and 5 ml, respectively). However, due to the wide variation in the size of commer- cially available spoons, dosing will not Lüllmann, Color Atlas of Pharmacology © 2000 Thieme All rights reserved. Usage subject to terms and conditions of license.
Drug Administration 9 5- Aqueous Eye 50 solution drops ml 20 drops = 1g Sterile isotonic Dosage: pH-neutral in drops 5- Alcoholic 50 solution ml 40 drops = 1g Viscous solution 10 0- Nose 50 drops 0m l Dosage: Solution in spoon Mixture A. Liquid preparations Mixing and forming by compression Drug ~0.5 – 500 mg Effervescent tablet Filler 30 – 250 mg Disintegrating 20 – 200 mg agent Tablet Capsule Other 30 – 15 mg excipients min 100 – 1000 mg max possible tablet size Coated tablet B. Solid preparations for oral application Capsule Time Coated Drug release tablet Capsule with coated drug pellets Matrix tablet C. Dosage forms controlling rate of drug dissolution Lüllmann, Color Atlas of Pharmacology © 2000 Thieme All rights reserved. Usage subject to terms and conditions of license.
10 Drug Administration The coated tablet contains a drug with- sit time, drug release can be timed to oc- in a core that is covered by a shell, e.g., a cur in the colon. wax coating, that serves to: (1) protect Drug liberation and, hence, absorp- perishable drugs from decomposing; (2) tion can also be spread out when the mask a disagreeable taste or odor; (3) drug is presented in the form of a granu- facilitate passage on swallowing; or (4) late consisting of pellets coated with a permit color coding. waxy film of graded thickness. Depend- Capsules usually consist of an ob- ing on film thickness, gradual dissolu- long casing — generally made of gelatin tion occurs during enteral transit, re- — that contains the drug in powder or leasing drug at variable rates for absorp- granulated form (See. p. 9, C). tion. The principle illustrated for a cap- In the case of the matrix-type tab- sule can also be applied to tablets. In this let, the drug is embedded in an inert case, either drug pellets coated with meshwork from which it is released by films of various thicknesses are com- diffusion upon being moistened. In con- pressed into a tablet or the drug is incor- trast to solutions, which permit direct porated into a matrix-type tablet. Con- absorption of drug (A, track 3), the use trary to timed-release capsules (Span- of solid dosage forms initially requires sules®), slow-release tablets have the ad- tablets to break up and capsules to open vantage of being dividable ad libitum; (disintegration) before the drug can be thus, fractions of the dose contained dissolved (dissolution) and pass within the entire tablet may be admin- through the gastrointestinal mucosal istered. lining (absorption). Because disintegra- This kind of retarded drug release tion of the tablet and dissolution of the is employed when a rapid rise in blood drug take time, absorption will occur level of drug is undesirable, or when ab- mainly in the intestine (A, track 2). In sorption is being slowed in order to pro- the case of a solution, absorption starts long the action of drugs that have a in the stomach (A, track 3). short sojourn in the body. For acid-labile drugs, a coating of wax or of a cellulose acetate polymer is used to prevent disintegration of solid dosage forms in the stomach. Accord- ingly, disintegration and dissolution will take place in the duodenum at nor- mal speed (A, track 1) and drug libera- tion per se is not retarded. The liberation of drug, hence the site and time-course of absorption, are subject to modification by appropriate production methods for matrix-type tablets, coated tablets, and capsules. In the case of the matrix tablet, the drug is incorporated into a lattice from which it can be slowly leached out by gastroin- testinal fluids. As the matrix tablet undergoes enteral transit, drug libera- tion and absorption proceed en route (A, track 4). In the case of coated tablets, coat thickness can be designed such that release and absorption of drug occur ei- ther in the proximal (A, track 1) or distal (A, track 5) bowel. Thus, by matching dissolution time with small-bowel tran- Lüllmann, Color Atlas of Pharmacology © 2000 Thieme All rights reserved. Usage subject to terms and conditions of license.
Drug Administration 11 Administration in form of Enteric- Tablet, Drops, Matrix Coated coated capsule mixture, tablet tablet with tablet effervescent delayed solution release 1 2 3 4 5 A. Oral administration: drug release and absorption Lüllmann, Color Atlas of Pharmacology © 2000 Thieme All rights reserved. Usage subject to terms and conditions of license.
12 Drug Administration Dosage Forms for Parenteral (1), the rectum or vagina. The resulting oily Pulmonary (2), Rectal or Vaginal (3), film spreads over the mucosa and en- and Cutaneous Application ables the drug to pass into the mucosa. Powders, ointments, and pastes Drugs need not always be administered (p. 16) are applied to the skin surface. In orally (i.e., by swallowing), but may also many cases, these do not contain drugs be given parenterally. This route usual- but are used for skin protection or care. ly refers to an injection, although enter- However, drugs may be added if a topi- al absorption is also bypassed when cal action on the outer skin or, more drugs are inhaled or applied to the skin. rarely, a systemic effect is intended. For intravenous, intramuscular, or Transdermal drug delivery subcutaneous injections, drugs are of- systems are pasted to the epidermis. ten given as solutions and, less fre- They contain a reservoir from which quently, in crystalline suspension for drugs may diffuse and be absorbed intramuscular, subcutaneous, or intra- through the skin. They offer the advan- articular injection. An injectable solu- tage that a drug depot is attached non- tion must be free of infectious agents, invasively to the body, enabling the pyrogens, or suspended matter. It drug to be administered in a manner should have the same osmotic pressure similar to an infusion. Drugs amenable and pH as body fluids in order to avoid to this type of delivery must: (1) be ca- tissue damage at the site of injection. pable of penetrating the cutaneous bar- Solutions for injection are preserved in rier; (2) be effective in very small doses airtight glass or plastic sealed contain- (restricted capacity of reservoir); and ers. From ampules for multiple or sin- (3) possess a wide therapeutic margin gle use, the solution is aspirated via a (dosage not adjustable). needle into a syringe. The cartridge am- pule is fitted into a special injector that enables its contents to be emptied via a needle. An infusion refers to a solution being administered over an extended period of time. Solutions for infusion must meet the same standards as solu- tions for injection. Drugs can be sprayed in aerosol form onto mucosal surfaces of body cav- ities accessible from the outside (e.g., the respiratory tract [p. 14]). An aerosol is a dispersion of liquid or solid particles in a gas, such as air. An aerosol results when a drug solution or micronized powder is reduced to a spray on being driven through the nozzle of a pressur- ized container. Mucosal application of drug via the rectal or vaginal route is achieved by means of suppositories and vaginal tablets, respectively. On rectal applica- tion, absorption into the systemic circu- lation may be intended. With vaginal tablets, the effect is generally confined to the site of application. Usually the drug is incorporated into a fat that solid- ifies at room temperature, but melts in Lüllmann, Color Atlas of Pharmacology © 2000 Thieme All rights reserved. Usage subject to terms and conditions of license.
Drug Administration 13 Sterile, iso-osmolar Ampule Cartridge Propellant gas 1 – 20 ml ampule 2 ml Drug solution With and without Often with fracture ring preservative Jet nebulizer 2 35 ºC Vaginal tablet Suppository Multiple-dose Infusion vial 50 – 100 ml, solution always with 500 – 1000 ml preservative 1 35 ºC Melting point 3 Backing layer Drug reservoir Adhesive coat Paste Ointment Transdermal delivery system (TDS) Drug release Powder Ointment TDS Time 12 24 h 4 A. Preparations for parenteral (1), inhalational (2), rectal or vaginal (3), and percutaneous (4) application Lüllmann, Color Atlas of Pharmacology © 2000 Thieme All rights reserved. Usage subject to terms and conditions of license.
14 Drug Administration Drug Administration by Inhalation mucociliary transport functions to re- move inspired dust particles. Thus, only Inhalation in the form of an aerosol a portion of the drug aerosol (~ 10 %) (p. 12), a gas, or a mist permits drugs to gains access to the respiratory tract and be applied to the bronchial mucosa and, just a fraction of this amount penetrates to a lesser extent, to the alveolar mem- the mucosa, whereas the remainder of branes. This route is chosen for drugs in- the aerosol undergoes mucociliary tended to affect bronchial smooth mus- transport to the laryngopharynx and is cle or the consistency of bronchial mu- swallowed. The advantage of inhalation cus. Furthermore, gaseous or volatile (i.e., localized application) is fully ex- agents can be administered by inhala- ploited by using drugs that are poorly tion with the goal of alveolar absorption absorbed from the intestine (isoprotere- and systemic effects (e.g., inhalational nol, ipratropium, cromolyn) or are sub- anesthetics, p. 218). Aerosols are ject to first-pass elimination (p. 42; bec- formed when a drug solution or micron- lomethasone dipropionate, budesonide, ized powder is converted into a mist or flunisolide, fluticasone dipropionate). dust, respectively. Even when the swallowed portion In conventional sprays (e.g., nebu- of an inhaled drug is absorbed in un- lizer), the air blast required for aerosol changed form, administration by this formation is generated by the stroke of a route has the advantage that drug con- pump. Alternatively, the drug is deliv- centrations at the bronchi will be higher ered from a solution or powder pack- than in other organs. aged in a pressurized canister equipped The efficiency of mucociliary trans- with a valve through which a metered port depends on the force of kinociliary dose is discharged. During use, the in- motion and the viscosity of bronchial haler (spray dispenser) is held directly mucus. Both factors can be altered in front of the mouth and actuated at pathologically (e.g., in smoker’s cough, the start of inspiration. The effective- bronchitis) or can be adversely affected ness of delivery depends on the position by drugs (atropine, antihistamines). of the device in front of the mouth, the size of aerosol particles, and the coordi- nation between opening of the spray valve and inspiration. The size of aerosol particles determines the speed at which they are swept along by inhaled air, hence the depth of penetration into the respiratory tract. Particles > 100 µm in diameter are trapped in the oropharyngeal cavity; those having dia- meters between 10 and 60 µm will be deposited on the epithelium of the bronchial tract. Particles < 2 µm in dia- meter can reach the alveoli, but they will be largely exhaled because of their low tendency to impact on the alveolar epithelium. Drug deposited on the mucous lin- ing of the bronchial epithelium is partly absorbed and partly transported with bronchial mucus towards the larynx. Bronchial mucus travels upwards due to the orally directed undulatory beat of the epithelial cilia. Physiologically, this Lüllmann, Color Atlas of Pharmacology © 2000 Thieme All rights reserved. Usage subject to terms and conditions of license.
Drug Administration 15 Depth of penetration of inhaled aerosolized drug solution 10% 90% Drug swept up is swallowed 100 µm Nasopharynx Larynx 10 µm Trachea-bronchi 1 cm/min 1 µm Bronchioli, alveoli Mucociliary transport As complete As little presystemic enteral elimination absorption as possible as possible Low systemic burden Ciliated epithelium A. Application by inhalation Lüllmann, Color Atlas of Pharmacology © 2000 Thieme All rights reserved. Usage subject to terms and conditions of license.
16 Drug Administration Dermatologic Agents Hydrophilic (aqueous) cream is an emulsion of an oil in water formed with Pharmaceutical preparations applied to the aid of an emulsifier; it may also be the outer skin are intended either to considered an oil-in-water emulsion of provide skin care and protection from an emulsifying ointment. noxious influences (A), or to serve as a All dermatologic agents having a vehicle for drugs that are to be absorbed lipophilic base adhere to the skin as a into the skin or, if appropriate, into the water-repellent coating. They do not general circulation (B). wash off and they also prevent (oc- clude) outward passage of water from Skin Protection (A) the skin. The skin is protected from dry- Protective agents are of several kinds to ing, and its hydration and elasticity in- meet different requirements according crease. to skin condition (dry, low in oil, Diminished evaporation of water chapped vs moist, oily, elastic), and the results in warming of the occluded skin type of noxious stimuli (prolonged ex- area. Hydrophilic agents wash off easily posure to water, regular use of alcohol- and do not impede transcutaneous out- containing disinfectants [p. 290], in- put of water. Evaporation of water is felt tense solar irradiation). as a cooling effect. Distinctions among protective agents are based upon consistency, phy- Dermatologic Agents as Vehicles (B) sicochemical properties (lipophilic, hy- In order to reach its site of action, a drug drophilic), and the presence of addi- (D) must leave its pharmaceutical pre- tives. paration and enter the skin, if a local ef- Dusting Powders are sprinkled on- fect is desired (e.g., glucocorticoid oint- to the intact skin and consist of talc, ment), or be able to penetrate it, if a magnesium stearate, silicon dioxide systemic action is intended (transder- (silica), or starch. They adhere to the mal delivery system, e.g., nitroglycerin skin, forming a low-friction film that at- patch, p. 120). The tendency for the drug tenuates mechanical irritation. Powders to leave the drug vehicle (V) is higher exert a drying (evaporative) effect. the more the drug and vehicle differ in Lipophilic ointment (oil ointment) lipophilicity (high tendency: hydrophil- consists of a lipophilic base (paraffin oil, ic D and lipophilic V, and vice versa). Be- petroleum jelly, wool fat [lanolin]) and cause the skin represents a closed lipo- may contain up to 10 % powder materi- philic barrier (p. 22), only lipophilic als, such as zinc oxide, titanium oxide, drugs are absorbed. Hydrophilic drugs starch, or a mixture of these. Emulsify- fail even to penetrate the outer skin ing ointments are made of paraffins and when applied in a lipophilic vehicle. an emulsifying wax, and are miscible This formulation can be meaningful with water. when high drug concentrations are re- Paste (oil paste) is an ointment quired at the skin surface (e.g., neomy- containing more than 10 % pulverized cin ointment for bacterial skin infec- constituents. tions). Lipophilic (oily) cream is an emul- sion of water in oil, easier to spread than oil paste or oil ointments. Hydrogel and water-soluble oint- ment achieve their consistency by means of different gel-forming agents (gelatin, methylcellulose, polyethylene glycol). Lotions are aqueous suspen- sions of water-insoluble and solid con- stituents. Lüllmann, Color Atlas of Pharmacology © 2000 Thieme All rights reserved. Usage subject to terms and conditions of license.
Drug Administration 17 Solid Liquid Powder Solution Aqueous Alcoholic Paste Dermatologicals solution tincture Oily paste Semi-solid Hydrogel Ointment Lotion Cream Lipophilic Hydrophilic Suspen- Emulsion ointment ointment sion Lipophilic Hydrophilic cream cream Fat, oil Water in oil Oil in water Gel, water Occlusive Permeable, coolant Perspiration impossible possible Dry, non-oily skin Oily, moist skin A. Dermatologicals as skin protectants Lipophilic drug Lipophilic drug Hydrophilic drug Hydrophilic drug in lipophilic in hydrophilic in lipophilic in hydrophilic base base base base Epithelium Stratum corneum Subcutaneous fat tissue B. Dermatologicals as drug vehicles Lüllmann, Color Atlas of Pharmacology © 2000 Thieme All rights reserved. Usage subject to terms and conditions of license.
18 Drug Administration From Application to Distribution this route is determined by both the in the Body physicochemical properties of the drug and the therapeutic requirements As a rule, drugs reach their target organs (acute vs. long-term effect). via the blood. Therefore, they must first Speed of absorption is determined enter the blood, usually the venous limb by the route and method of application. of the circulation. There are several pos- It is fastest with intravenous injection, sible sites of entry. less fast which intramuscular injection, The drug may be injected or infused and slowest with subcutaneous injec- intravenously, in which case the drug is tion. When the drug is applied to the introduced directly into the blood- oral mucosa (buccal, sublingual route), stream. In subcutaneous or intramus- plasma levels rise faster than with con- cular injection, the drug has to diffuse ventional oral administration because from its site of application into the the drug preparation is deposited at its blood. Because these procedures entail actual site of absorption and very high injury to the outer skin, strict require- concentrations in saliva occur upon the ments must be met concerning tech- dissolution of a single dose. Thus, up- nique. For that reason, the oral route take across the oral epithelium is accel- (i.e., simple application by mouth) in- erated. The same does not hold true for volving subsequent uptake of drug poorly water-soluble or poorly absorb- across the gastrointestinal mucosa into able drugs. Such agents should be given the blood is chosen much more fre- orally, because both the volume of fluid quently. The disadvantage of this route for dissolution and the absorbing sur- is that the drug must pass through the face are much larger in the small intes- liver on its way into the general circula- tine than in the oral cavity. tion. This fact assumes practical signifi- Bioavailability is defined as the cance with any drug that may be rapidly fraction of a given drug dose that reach- transformed or possibly inactivated in es the circulation in unchanged form the liver (first-pass hepatic elimination; and becomes available for systemic dis- p. 42). Even with rectal administration, tribution. The larger the presystemic at least a fraction of the drug enters the elimination, the smaller is the bioavail- general circulation via the portal vein, ability of an orally administered drug. because only veins draining the short terminal segment of the rectum com- municate directly with the inferior vena cava. Hepatic passage is circumvented when absorption occurs buccally or sublingually, because venous blood from the oral cavity drains directly into the superior vena cava. The same would apply to administration by inhalation (p. 14). However, with this route, a local effect is usually intended; a systemic ac- tion is intended only in exceptional cas- es. Under certain conditions, drug can also be applied percutaneously in the form of a transdermal delivery system (p. 12). In this case, drug is slowly re- leased from the reservoir, and then pen- etrates the epidermis and subepidermal connective tissue where it enters blood capillaries. Only a very few drugs can be applied transdermally. The feasibility of Lüllmann, Color Atlas of Pharmacology © 2000 Thieme All rights reserved. Usage subject to terms and conditions of license.
Drug Administration 19 Inhalational Sublingual buccal Oral Intravenous Aorta Transdermal Subcutaneous Distribution in body Intramuscular Rectal A. From application to distribution Lüllmann, Color Atlas of Pharmacology © 2000 Thieme All rights reserved. Usage subject to terms and conditions of license.
20 Cellular Sites of Action Potential Targets of Drug Action agents acting in the cell’s interior need to penetrate the cell membrane. Drugs are designed to exert a selective The cell membrane basically con- influence on vital processes in order to sists of a phospholipid bilayer (80Å = alleviate or eliminate symptoms of dis- 8 nm in thickness) in which are embed- ease. The smallest basic unit of an or- ded proteins (integral membrane pro- ganism is the cell. The outer cell mem- teins, such as receptors and transport brane, or plasmalemma, effectively de- molecules). Phospholipid molecules marcates the cell from its surroundings, contain two long-chain fatty acids in es- thus permitting a large degree of inter- ter linkage with two of the three hy- nal autonomy. Embedded in the plas- droxyl groups of glycerol. Bound to the malemma are transport proteins that third hydroxyl group is phosphoric acid, serve to mediate controlled metabolic which, in turn, carries a further residue, exchange with the cellular environment. e.g., choline, (phosphatidylcholine = lec- These include energy-consuming ithin), the amino acid serine (phosphat- pumps (e.g., Na, K-ATPase, p. 130), car- idylserine) or the cyclic polyhydric alco- riers (e.g., for Na/glucose-cotransport, p. hol inositol (phosphatidylinositol). In 178), and ion channels e.g., for sodium terms of solubility, phospholipids are (p. 136) or calcium (p. 122) (1). amphiphilic: the tail region containing Functional coordination between the apolar fatty acid chains is lipophilic, single cells is a prerequisite for viability the remainder – the polar head – is hy- of the organism, hence also for the sur- drophilic. By virtue of these properties, vival of individual cells. Cell functions phospholipids aggregate spontaneously are regulated by means of messenger into a bilayer in an aqueous medium, substances for the transfer of informa- their polar heads directed outwards into tion. Included among these are “trans- the aqueous medium, the fatty acid mitters” released from nerves, which chains facing each other and projecting the cell is able to recognize with the into the inside of the membrane (3). help of specialized membrane binding The hydrophobic interior of the sites or receptors. Hormones secreted phospholipid membrane constitutes a by endocrine glands into the blood, then diffusion barrier virtually imperme- into the extracellular fluid, represent able for charged particles. Apolar parti- another class of chemical signals. Final- cles, however, penetrate the membrane ly, signalling substances can originate easily. This is of major importance with from neighboring cells, e.g., prostaglan- respect to the absorption, distribution, dins (p. 196) and cytokines. and elimination of drugs. The effect of a drug frequently re- sults from interference with cellular function. Receptors for the recognition of endogenous transmitters are obvious sites of drug action (receptor agonists and antagonists, p. 60). Altered activity of transport systems affects cell func- tion (e.g., cardiac glycosides, p. 130; loop diuretics, p. 162; calcium-antago- nists, p. 122). Drugs may also directly interfere with intracellular metabolic processes, for instance by inhibiting (phosphodiesterase inhibitors, p. 132) or activating (organic nitrates, p. 120) an enzyme (2). In contrast to drugs acting from the outside on cell membrane constituents, Lüllmann, Color Atlas of Pharmacology © 2000 Thieme All rights reserved. Usage subject to terms and conditions of license.
Cellular Sites of Action 21 1 Neural control D Nerve Transmitter Receptor Ion channel Cellular Hormonal transport control systems for Hormones controlled transfer of substrates D Hormone D receptors Transport molecule Enzyme D Direct action on metabolism D = Drug 2 3 Choline D D Phosphoric acid Phospholipid matrix Glycerol Protein Fatty acid Effect Intracellular site of action A. Sites at which drugs act to modify cell function Lüllmann, Color Atlas of Pharmacology © 2000 Thieme All rights reserved. Usage subject to terms and conditions of license.