Administration in form of
Drops, mixture, effervescent solution
the rectum or vagina. The resulting oily film spreads over the mucosa and enables the drug to pass into the mucosa.
Powders, ointments, and pastes (p. 16) are applied to the skin surface. In many cases, these do not contain drugs but are used for skin protection or care. However, drugs may be added if a topical action on the outer skin or, more rarely, a systemic effect is intended.
Transdermal drug delivery systems are pasted to the epidermis. They contain a reservoir from which drugs may diffuse and be absorbed through the skin. They offer the advantage that a drug depot is attached non-invasively to the body, enabling the drug to be administered in a manner similar to an infusion. Drugs amenable to this type of delivery must: (1) be capable of penetrating the cutaneous barrier; (2) be effective in very small doses (restricted capacity of reservoir); and (3) possess a wide therapeutic margin (dosage not adjustable).
posage Forms for Parenteral (1), Pulmonary (2), Rectal or Vaginal (3), and Cutaneous Application
Drugs need not always be administered orally (i.e., by swallowing), but may also be given parenterally. This route usually refers to an injection, although enter-al absorption is also bypassed when drugs are inhaled or applied to the skin.
For intravenous, intramuscular, or subcutaneous injections, drugs are often given as solutions and, less frequently, in crystalline suspension for intramuscular, subcutaneous, or intra-articular injection. An injectable solution must be free of infectious agents, pyrogens, or suspended matter. It should have the same osmotic pressure and pH as body fluids in order to avoid tissue damage at the site of injection. Solutions for injection are preserved in airtight glass or plastic sealed containers. From ampules for multiple or single use, the solution is aspirated via a needle into a syringe. The cartridge ampule 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 solutions for injection.
Drugs can be sprayed in aerosol form onto mucosal surfaces of body cavities 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 pressurized container.
Mucosal application of drug via the rectal or vaginal route is achieved by means of suppositories and vaginal tablets, respectively. On rectal application, absorption into the systemic circulation 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 solidifies 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 by inhalation
Inhalation in the form of an aerosol (p. 12), a gas, or a mist permits drugs to be applied to the bronchial mucosa and, to a lesser extent, to the alveolar membranes. This route is chosen for drugs intended to affect bronchial smooth muscle or the consistency of bronchial mucus. Furthermore, gaseous or volatile agents can be administered by inhalation with the goal of alveolar absorption and systemic effects (e.g., inhalational anesthetics, p. 218). Aerosols are formed when a drug solution or micron-ized powder is converted into a mist or dust, respectively.
In conventional sprays (e.g., nebulizer), the air blast required for aerosol formation is generated by the stroke of a pump. Alternatively, the drug is delivered from a solution or powder packaged in a pressurized canister equipped with a valve through which a metered dose is discharged. During use, the inhaler (spray dispenser) is held directly in front of the mouth and actuated at the start of inspiration. The effectiveness of delivery depends on the position of the device in front of the mouth, the size of aerosol particles, and the coordination 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 |im in diameter are trapped in the oropharyngeal cavity; those having diameters between 10 and 60 |m will be deposited on the epithelium of the bronchial tract. Particles < 2 |m in diameter 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 lining 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 Lullmann, Color Atlas of Pharmacology © 2000 Thieme All rights reserved. Usage subject to terms and conditions of license.
mucociliary transport functions to remove inspired dust particles. Thus, only a portion of the drug aerosol (~ 10%) gains access to the respiratory tract and just a fraction of this amount penetrates the mucosa, whereas the remainder of the aerosol undergoes mucociliary transport to the laryngopharynx and is swallowed. The advantage of inhalation (i.e., localized application) is fully exploited by using drugs that are poorly absorbed from the intestine (isoprotere-nol, ipratropium, cromolyn) or are subject to first-pass elimination (p. 42; bec-lomethasone dipropionate, budesonide, flunisolide, fluticasone dipropionate).
Even when the swallowed portion of an inhaled drug is absorbed in unchanged form, administration by this route has the advantage that drug concentrations at the bronchi will be higher than in other organs.
The efficiency of mucociliary transport depends on the force of kinociliary motion and the viscosity of bronchial mucus. Both factors can be altered pathologically (e.g., in smoker's cough, bronchitis) or can be adversely affected by drugs (atropine, antihistamines).
Pharmaceutical preparations applied to the outer skin are intended either to provide skin care and protection from noxious influences (A), or to serve as a vehicle for drugs that are to be absorbed into the skin or, if appropriate, into the general circulation (B).
Skin Protection (A)
Protective agents are of several kinds to meet different requirements according to skin condition (dry, low in oil, chapped vs moist, oily, elastic), and the type of noxious stimuli (prolonged exposure to water, regular use of alcohol-containing disinfectants [p. 290], intense solar irradiation).
Distinctions among protective agents are based upon consistency, phy-sicochemical properties (lipophilic, hy-drophilic), and the presence of additives.
Dusting Powders are sprinkled onto the intact skin and consist of talc, magnesium stearate, silicon dioxide (silica), or starch. They adhere to the skin, forming a low-friction film that attenuates mechanical irritation. Powders exert a drying (evaporative) effect.
Lipophilic ointment (oil ointment) consists of a lipophilic base (paraffin oil, petroleum jelly, wool fat [lanolin]) and may contain up to 10 % powder materials, such as zinc oxide, titanium oxide, starch, or a mixture of these. Emulsifying ointments are made of paraffins and an emulsifying wax, and are miscible with water.
Paste (oil paste) is an ointment containing more than 10% pulverized constituents.
Lipophilic (oily) cream is an emulsion of water in oil, easier to spread than oil paste or oil ointments.
Hydrogel and water-soluble ointment achieve their consistency by means of different gel-forming agents (gelatin, methylcellulose, polyethylene glycol). Lotions are aqueous suspensions of water-insoluble and solid constituents.
Hydrophilic (aqueous) cream is an emulsion of an oil in water formed with the aid of an emulsifier; it may also be considered an oil-in-water emulsion of an emulsifying ointment.
All dermatologic agents having a lipophilic base adhere to the skin as a water-repellent coating. They do not wash off and they also prevent (occlude) outward passage of water from the skin. The skin is protected from drying, and its hydration and elasticity increase.
Diminished evaporation of water results in warming of the occluded skin area. Hydrophilic agents wash off easily and do not impede transcutaneous output of water. Evaporation of water is felt as a cooling effect.
Dermatologic Agents as Vehicles (B)
In order to reach its site of action, a drug (D) must leave its pharmaceutical preparation and enter the skin, if a local effect is desired (e.g., glucocorticoid ointment), or be able to penetrate it, if a systemic action is intended (transdermal delivery system, e.g., nitroglycerin patch, p. 120). The tendency for the drug to leave the drug vehicle (V) is higher the more the drug and vehicle differ in lipophilicity (high tendency: hydrophil-ic D and lipophilic V, and vice versa). Because the skin represents a closed lipo-philic barrier (p. 22), only lipophilic drugs are absorbed. Hydrophilic drugs fail even to penetrate the outer skin when applied in a lipophilic vehicle. This formulation can be meaningful when high drug concentrations are required at the skin surface (e.g., neomy-cin ointment for bacterial skin infections).
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