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Nitrofurazone

5-Nitro-2-furaldehyde semicarbazone (Furacin) occurs as a lemon-yellow crystalline solid that is sparingly soluble in water and practically insoluble in organic solvents. Nitrofurazone is chemically stable, but moderately light sensitive.

It is used topically in the treatment of burns, especially when bacterial resistance to other agents may be a concern. It may also be used to prevent bacterial infection associated with skin grafts. Nitrofurazone has a broad spectrum of activity against Gram-positive and Gram-negative bacteria, but it is not active against fungi. It is bactericidal against most bacteria commonly causing surface infections, including S. aureus, Streptococcus spp., e. coli, Clostridium perfringens, Enterobacter (Aerobacter) aero-genes, and Proteus spp.; however, p. aeruginosa strains are resistant.

Nitrofurazone is marketed in solutions, ointments, and suppositories in a usual concentration of 0.2%.

Furazolidone

3-[(5-Nitrofurylidene)amino]-2-oxazolidinone (Furoxone) occurs as a yellow crystalline powder with a bitter aftertaste. It is insoluble in water or alcohol. Furazolidone has bactericidal activity against a relatively broad range of intestinal pathogens, including s. aureus, E. coli, Salmonella, Shigella, Proteus spp., Enterobacter, and Vibrio cholerae. It is also active against the protozoan Giardia lamblia. It is recommended for the oral treatment of bacterial or proto-zoal diarrhea caused by susceptible organisms. The usual adult dosage is 100 mg 4 times daily.

The mechanism of antimicrobial action of the nitrofurans has been extensively studied, but it still is not fully understood. In addition to their antimicrobial actions, the nitrofurans are known to be mutagenic and carcinogenic under certain conditions. It is thought that DNA damage caused by metabolic reaction products may be involved in these cellular effects.

Only a small fraction of an orally administered dose of furazolidone is absorbed. Approximately 5% of the oral dose is detectable in the urine in the form of several metabolites. Some gastrointestinal distress has been reported with its use. Alcohol should be avoided when furazolidone is being used because the drug can inhibit aldehyde dehydrogenase.

Nitrofurantoin

Nitrofurantoin, 1-(5-nitro-2-furfurylidene)- 1-aminohydan-toin (Furadantin, Macrodantin), is a nitrofuran derivative that is suitable for oral use. It is recommended for the treatment of urinary tract infections caused by susceptible strains of e. coli, enterococci, s. aureus, Klebsiella, Enterobacter, and Proteus spp. The most common side effects are gastrointestinal (anorexia, nausea, and vomiting); however, hy-persensitivity reactions (pneumonitis, rashes, hepatitis, and hemolytic anemia) have occasionally been observed. A macrocrystalline form (Macrodantin) is claimed to improve gastrointestinal tolerance without interfering with oral absorption.

Methenamine and Its Salts

Methenamine

The activity of hexamethylenetetramine (Urotropin, Uritone) depends on the liberation of formaldehyde. The compound is prepared by evaporating a solution of formaldehyde and strong ammonia water to dryness.

The free base exists as an odorless, white crystalline powder that sublimes at about 260°C. It dissolves in water to form an alkaline solution and liberates formaldehyde when warmed with mineral acids. Methenamine is a weak base with a pKa of 4.9.

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