ampul form and used by inhalation or orally in alcohol solution. Currently, it is recommended for treating cyanide poisoning; although not the best antidote, it does not require intravenous injections.
Amyl nitrite is a yellowish liquid with an ethereal odor and a pungent taste. It is volatile and inflammable at room temperature. Amyl nitrite vapor forms an explosive mixture in air or oxygen. Inhalation of the vapor may involve definite explosion hazards if a source of ignition is present, as both room and body temperatures are within the flammability range of amyl nitrite mixtures with either air or oxygen. It is nearly insoluble in water but is miscible with organic solvents. The nitrite also will decompose in valeric acid and nitric acid.
Nitroglycerin. Glyceryl trinitrate is the trinitrate ester of glycerol and is listed as available in tablet form in the usp. It is prepared by carefully adding glycerin to a mixture of nitric and fuming sulfuric acids. This reaction is exothermic, and the reaction mixture must be cooled to between 10°C and 20°C.
The ester is a colorless oil, with a sweet, burning taste. It is only slightly soluble in water, but it is soluble in organic solvents.
Injection Nitrobid IV
Nitroglycerin is used extensively as an explosive in dynamite. A solution of the ester, if spilled or allowed to evaporate, will leave a residue of nitroglycerin. To prevent an explosion of the residue, the ester must be decomposed by adding alkali. Even so, the material dispensed is so dilute that the risk of explosions does not exist. It has a strong vasodilating action and, because it is absorbed through the skin, is prone to cause headaches among workers associated with its manufacture. This transdermal penetration is why nitroglycerin is useful in a patch formulation. In medicine, it has the action typical of nitrites, but its action develops more slowly and is of longer duration. Of all the known coronary vasodilatory drugs, nitroglycerin is the only one capable of stimulating the production of coronary collateral circulation and the only one able to prevent experimental myocardial infarction by coronary occlusion.
Previously, the nitrates were thought to be hydrolyzed and reduced in the body to nitrites, which then lowered the blood pressure. This is not true, however. The mechanism of vasodilation of nitroglycerin through its formation of NO is described previously.
Nitroglycerin tablet instability was reported in molded sublingual tablets.8 The tablets, although uniform when manufactured, lost potency both because of volatilization of nitroglycerin into the surrounding materials in the container and intertablet migration of the active ingredient. Nitroglycerin may be stabilized in molded tablets by incorporating a "fixing" agent such as polyethylene glycol 400 or polyethylene glycol 4000.9 In addition to sublingual tablets, the drug has been formulated into an equally effective lingual aerosol for patients who have problems with dissolution of sublingual preparations because of dry mucous membranes. Transdermal nitroglycerin preparations appear to be less effective than other long-acting nitrates, as absorption from the skin is variable.
Diluted Erythrityl Tetranitrate, USP. Erythritol tetranitrate, 1,2,3,4-butanetetrol, tetranitrate (r*, s*)-(Cardilate), is the tetranitrate ester of erythritol and nitric acid. It is prepared in a manner analogous to that used for nitroglycerin. The result is a solid, crystalline material. This ester is also very explosive and is diluted with lactose or other suitable inert diluents to permit safe handling; it is slightly soluble in water and soluble in organic solvents.
Erythrityl tetranitrate requires slightly more time than ni-troglycerin to produce its effect, which is of longer duration. It is useful when mild, gradual, and prolonged vascular dilation is warranted. The drug is used in the treatment of, and as prophylaxis against, attacks of angina pectoris and to reduce blood pressure in arterial hypertonia.
Erythrityl tetranitrate produces a reduction of cardiac preload as a result of pooling blood on the venous side of the circulatory system by its vasodilating action. This action results in a reduction of blood pressure on the arterial side during stressful situations and is an important factor in preventing the precipitation of anginal attacks.
Diluted Pentaerythritol Tetranitrate, USP. Pen-taerythritol tetranitrate, 2,2-bis (hydroxymethyl)-1,3-propanediol tetranitrate (Peritrate, Pentritol), is a white, crystalline material with a melting point of 140°C. It is insoluble in water, slightly soluble in alcohol, and readily soluble in acetone. The drug is a nitric acid ester of the tetrahydric alcohol pentaerythritol and is a powerful explosive. Accordingly, it is diluted with lactose, mannitol, or other suitable inert diluents to permit safe handling.
It relaxes smooth muscle of smaller vessels in the coronary vascular tree. Pentaerythritol tetranitrate is used pro-phylactically to reduce the severity and frequency of anginal attacks and is usually administered in sustained-release preparations to increase its duration of action.
Diluted Isosorbide Dinitrate, USP. Isosorbide dinitrate, 1,4:3,6-dianhydro-d-glucitol dinitrate (Isordil, Sorbitrate), occurs as a white, crystalline powder. Its water solubility is about 1 mg/mL.
Isosorbide dinitrate, as a sublingual or chewable tablet, is effective in the treatment or prophylaxis of acute anginal attacks. When it is given sublingually, the effect begins in about 2 minutes, with a shorter duration of action than when it is given orally. Oral tablets are not effective in acute anginal episodes; the onset of action ranges from 15 to 30 minutes. The major route of metabolism involves den-itration to isosorbide 5-mononitrate. This metabolite has a much longer half-life than the parent isosorbide dinitrate. As such, this particular metabolite is marketed in a tablet form that has excellent bioavailability with much less firstpass metabolism than isosorbide dinitrate. Isosorbide is marketed as a combination therapy with hydralazine under the tradename BiDil specifically for African Americans with CHF.
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