Gaseous drugs

In critical evaluation of the effect of a gas, vapor, or aerosol inhaled in to the respiratory tract of an animal, the dosimetric method has been recommended (Oberst, 1961). However, due to the complexity of measuring the various parameters simultaneously, only a few studies on gaseous drugs or chemicals have employed the dosimetric method (Weston and Karel, 1946 Adams et al., 1952 Leong and MacFarland, 1965 Landy et al., 1983 Stott and McKenna, 1984 Dallas et al., 1986, 1989). For studies on liquid or powdery aerosols, modified techniques such as intratracheal instillation (Brain et al., 1976) or endotracheal nebulization (Leong et al., 1988) were used to deliver an exact dose of the test material into the lower respiratory tract (LRT) while bypassing the URT and ignoring the ventilatory parameters. 

Gaseous drugs reach the alveoli. This mainly applies to inhalation anesthetics (chloroform, ether, N2O, and their more modem replacements). Very rapid transition into the bloodstream - very rapid onset of action. 

CGA V-7 is not applicable to mixtures of medical gases, that is, gaseous drugs or gaseous medical devices. CGA V-1 covers connections for medical gas mixtures [1]. 

Antiflatulents are used for die relief of painful symptoms of excess gas in the digestive tract. These drugs are useful as adjunctive treatment of any condition in which gas retention may be a problem (ie, postoperative gaseous distention, air swallowing, dyspepsia, peptic ulcer, irritable colon, or diverticulosis). In addition to its use for tiie relief of intestinal gas, charcoal may be used in the prevention of nonspecific pruritus associated with kidney dialysis treatment and as an antidote in poisoning. Simethicone is in some antacid products, such as Mylanta liquid and Di-Gel liquid. 

Disperse systems can be classified in various ways. Classification based on the physical state of the two constituent phases is presented in Table 1. The dispersed phase and the dispersion medium can be either solids, liquids, or gases. Pharmaceutically most important are suspensions, emulsions, and aerosols. (Suspensions and emulsions are described in detail in Secs. IV and V pharmaceutical aerosols are treated in Chapter 14.) A suspension is a solid/liquid dispersion, e.g., a solid drug that is dispersed within a liquid that is a poor solvent for the drug. An emulsion is a li-quid/liquid dispersion in which the two phases are either completely immiscible or saturated with each other. In the case of aerosols, either a liquid (e.g., drug solution) or a solid (e.g., fine drug particles) is dispersed within a gaseous phase. There is no disperse system in which both phases are gases. 

Ignoring the physical aspects of a given formulation can be disastrous, since the stability of the drug entity can be strongly affected by its matrix [3], A wide variety of reactions are known to take place in the solid state [4], the pathway of which can be dramatically different when compared with how the same reaction would proceed in the liquid or gaseous phase [5]. 

Local administration of NO to the lungs has been shown to reverse pulmonary hypertension in animal models [103], importantly with no systemic side effects. This is likely to be as a result of surplus NO being removed as nitrosyl-hemoglobin [104]. Such advantages of gaseous NO were first reported in 1991 [105, 106]. In 1999 and 2001 NO gas was approved as a drug in the USA and European Union, for treating hypoxemic respiratory failure in infants [107]. 

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. 

Peptide neurotransmitters present problems for the drug designer because they are too large. Gaseous neurotransmitters likewise present problems for the dmg designer, but... 

The volatile liquids and gases are given by inhalation route. The drugs may be given as solid particles, as nebulized particles from solutions or in the form of vapours. The volatile substances include gaseous... 

Drugs may be solid at room temperature (eg, aspirin, atropine), liquid (eg, nicotine, ethanol), or gaseous (eg, nitrous oxide). These factors often determine the best route of administration. The most common routes of administration are described in Chapter 3. The various classes of organic compounds—carbohydrates, proteins, lipids, and their constituents—are all represented in pharmacology. 

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