Chemical Structure and Classification
Furazolidone is a classic representative of synthetic antimicrobial agents known as nitrofuran derivatives. The chemical architecture of all drugs in this group follows a single principle, which is essential to understand for pharmacology exams.
The basic core of the molecule is a furan ring. A critically important, mandatory element without which the drug loses its antimicrobial activity is the nitro group ($-NO_2$), attached strictly at the C5 position.
Differences among drugs within this group are due to a variable element—different substituents (radicals) at the C2 position. It is this radical that determines which specific drug is synthesized: furazolidone, nitrofurantoin (furadantin), furazidin (furagin), nitrofural (nitrofurazone), or nifuroxazide (enterofuryl).
Pharmacokinetics: Why Does the Drug Work in the Intestine?
A key pharmacokinetic characteristic of furazolidone is its extremely low bioavailability when administered orally. The drug is very poorly absorbed in the gastrointestinal tract. In general pharmacology, low absorption is often viewed as a drawback, but for agents intended to treat intestinal infections, this is a major therapeutic advantage.
Due to the lack of systemic absorption, furazolidone is not distributed throughout the body; instead, it accumulates, creating a stably high concentration of the active substance directly in the intestinal lumen. It acts locally, destroying the pathogenic flora. Another nitrofuran, nifuroxazide, which is used for gastrointestinal infections (enterocolitis and acute diarrhea), possesses a similar pharmacokinetic profile.
Indications: Bacteria and Protozoa
The spectrum of activity covers both bacterial and protozoal infections. The main therapeutic targets include:
- Giardiasis. Due to its accumulation in the intestinal lumen, the drug effectively targets protozoa parasitizing the gastrointestinal tract.
- Trichomoniasis. The causative agent of the disease is Trichomonas vaginalis. The main goal of pharmacotherapy in this case is complete eradication of the pathogen. It is important to remember that the primary drug class for treating trichomoniasis is nitroimidazoles (systemic tablets and vaginal suppositories of metronidazole, ornidazole, tinidazole). Furazolidone serves as an alternative agent, prescribed when the primary drug class cannot be used for any reason.
Dosing Regimen and Prescription Guidelines
The drug is administered exclusively via the oral route. For adult patients, the therapeutic limits in prescribing references are set as follows:
- Formulation: 0.05 g tablets.
- Standard single dose: 0.1–0.15 g (corresponding to 2–3 tablets at a time).
- Maximum single dose: 0.2 g (maximum 4 tablets per single dose).
- Maximum daily dose: 0.8 g (maximum 16 tablets per day).
Prescription Example: Rp.: Tab. Furazolidoni 0.05 D.t.d. N. 20 S. Take 2 tablets (0.1 g) orally 4 times a day.