Types of Inhalants

Chnical and epidemiological observations suggest that inhalant use in humans occurs along a continuum, with considerable variability in usage patterns among individuals as a function of age, gender, socioeconomic status, ethnicity, avahabihty and type of inhalant, and other clinical variables. As a general rule, it is expected that as inhalant consumption and frequency of intoxication increase, the incidence and severity of medical and psychosocial problems wiU increase. 

NOTE Other inhalers are becoming available in addition to those illustrated above. Different types of inhalers require different techniques. 

HCG human chorionic gonadotropin HCL hairy cell leukemia Hct hematocrit HCTZ hydrochlorothiazide HD hemodialysis HDAC histone deacetylase Hep hepatitis hepatotox hepatotoxicity HER2 type of cancer gene HF heart failure HFA designation for type of inhalation device Hgb hemoglobin HIT/HITTS heparin-mduced thrombocytopenia... 

Even when the appropriate inhaler is chosen, the influence of the disease state cannot be ignored. Disease states can influence the dimension and properties of the airways and hence the disposition of any inhaled drug. Thus, great care must be taken when extrapolating the findings based on intratracheal administration to different animal species in order to predict deposition profiles after inhalation of aerosol formulations by patients suffering from airway disease. DPIs are not appropriate in many diseases when the ability to have sufficient airflow is hindered. Since many diseases that we would like to treat via pulmonary administration of biomolecules cause a decrease in airflow, we must be careful in the decision of which type of inhalation mechanism to choose. 

Other researchers have found gender differences in the type of inhalant preferred. For instance, in a Virginia study published in the American Journal of Drug and Alcohol Abuse (October 1999), males were significantly more likely than females to abuse gasoline and females were significantly more likely to abuse hair spray than their male age peers. 

Four types of inhalants are abused (1) anesthetic gases (2) industrial solvents, including a variety of hydrocarbons, such as toluene (3) aerosol propellants, such as various fluorocarbons and (4) organic nitrites, such as amyl or butyl nitrite. The mode of action of the inhalant anesthetics has been discussed in Chapter 25 General Anesthetics. 

Three different types of inhalers are used to deliver drugs to the deep lung. Nebulizers, the oldest type of inhaler, work by producing a mist of aqueous, drug-containing droplets. The drug can be either dissolved or suspended in the water phase. In a pressurized metered dose inhaler (pMDI), the drug is... 

Q8 The dry-powder type of inhaler used to deliver bronchodilators and corticosteroids to the lung by inhalation can sometimes irritate the airways and cause further bronchoconstriction. It is useful to nebulize the drug, that is deliver it to the lung in solution as an aerosol. So the chief advantage of the nebulizer is that it allows drugs to be delivered deep into Carmen s lung, without causing irritation and bronchoconstriction. 

Figure 1.1 Inhalants are the fourth most popular drug of abuse among high-school students. In 2000, more than 2 million Americans aged 12 to 17 had used inhalants at least once in their lifetime. In this graph, the inhalants are grouped by type. Volatile solvents were the most popular type of inhalant used, with 3.9% of individuals inhaling glue, shoe polish, or toluene.

Figure 3.3 Group VI lA of the periodic table of the elements, shown here, contains the halogens, including the elements fluorine (F), chlorine (Ci), and bromine (Br). The haiogens are nonmetais with strong, unpieasant odors that can burn flesh. One type of inhalant is the haiogenated hydrocarbon where haiogen atoms are attached to a hydrocarbon moiecuie.

Since inhalant abusers typically abuse a number of types of inhalants, a thorough physical examination and detailed history of the compounds they have abused is critical. This is followed by treatments for the medical conditions that have been caused by the inhalant(s) abused. Treatment for inhalant abusers is often complicated by the fact that inhalant abusers use multiple drugs (Figure 8.2). 

Inhalers are designed to help medication to be delivered directly into the lungs, where it will act mainly on the lung tissue and systemic effects will be minimised. The doses employed in inhalers are significantly lower than those used in oral medication, so the incidence of side-effects will be reduced. There are a number of different types of inhaler available ... 

If more than one type of inhaled medication is taken it is important to take them in the correct order. Bronchodilating inhalers are used first to help open the airways. These are followed by corticosteroid inhalers. This ensures that the airways are open when the corticosteroid is administered, allowing as much of the dose as possible to be absorbed. 

If more than one type of inhaled medication is taken it is important to take them in the correct order. 

Children under the age of 12 years generally cannot use this type of inhaler successfully unless it has a spacer device (see Section 9.4.2). 

One advantage with this type of inhaler is that there is an indicator on the side showing how many doses are left in the inhaler. When approximately 20 doses are left a red mark appears to prompt the patient to order a new inhaler. 

The patient factors enter into play in several ways. The effectiveness of all aerosol delivery systems depends to some extent on the ability of the patients to use them properly. This has been shown for different types of inhalation systems, such as metered-dose inhalers [28,29] and the breath-driven powder generators [15,30]. The second determinant is the state of the patient s airways. These effects are discussed in greater detail in the following section. 

The medicine cabinet of the future may hold various types of inhalable drags that will replace not only dreaded injections, but also drugs with numerous side effects when taken orally. New approaches will lend support to the broad challenge of delivering biotherapentics and other medications to the Inngs. 

Unlike most other drug delivery systems, those in the respiratory area can have a major influence on physician/patient acceptance. A wide range of devices are available in the three main categories of dry powder inhalers (DPIs) and metered dose inhalers (MDIs), i.e., pressurised aerosols and nebulisers. The preferred type of inhaler varies considerably between countries (e.g., DPIs in Scandinavia and MDIs in the United States), and between patient groups (e.g., nebulisers for paediatrics). 

Slightly different terminology is used in the two regions when classifying various types of inhaled products. These are compared in Table 16.1. 

Many years ago, the USA agreed with other comitries to stop using CECs (chlorofluorocarbons) as propellants in aerosols because they contribute to the destruction of the atmospheric ozone layer. Until recently, formulary exemptions were made for inhalers that contained CECs. The pMDI remains the most popular type of inhaler used by people with asthma, with a different propellant called hydrofluo-roalkane (HEA), also referred to as CFC-free propellant. It may be less powerful and have a different taste which could impair compliance and efficacy in children accustomed to using their old inhaler. The DPI is the... 

The efficiency of DPI devices, in terms of lung and alveolar deposition, varies with the type of inhaler, the drug formulation, and the inspiratory flow rate (81). The effect of these factors are discussed briefly in the following paragraphs. 

Recognizing the fact that pMDIs were the most widely used form of inhaled therapy and available in all markets for all types of inhaled respiratory medicine, it was felt that their use did justify an essential use exemption from the Montreal Protocol. Dry-powder devices were recognized as an alternative for many, but they were not available in all countries for all medicines and were not always suitable for the young and those with low inspiratory flow rates also, they may not be suitable in certain humid climates. In some markets their extra cost would also deprive many of necessary treatment. 

MMAD is frequently presented as the parameter characterising aerosols from inhalation devices best. This is not true however. To judge the quality of a therapeutic aerosol from a particular type of inhaler, more information is needed. The MMAD does not give any information about the size distribution of the aerosol particles. Substantial mass fractions may be outside the desired size range for adequate deposition of active substance in the target area, even when MMAD looks very favourable. Moreover, MMAD does not give information about the mass fraction of the dose (label claim) that has been delivered within the desired size range. For aU types of inhalers, the delivered fine particle dose (FPD) is much lower than the label claim and this may vary from 10 % to 60 % for DPIs and up to 90 % for... 

Wong and Hargreave (245) have written an excellent review about the bioequivalence of metered-dose inhaled medications. The article is written for comparisons of generic drugs with the original. It is, however, also relevant for comparison between different administration systems. The authors discuss the criteria for equivalence of medications in in vitro studies it should be close to 15% of the innovator. They also discuss the different main types of inhalation drugs (e.g., bronchodilators, steroids, and antiallergic aerosols). 

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