Ophthalmic forms: Sulfacetamide
Sulfacetamide (known as Albucid) is available as eye drops and ointments. The drug penetrates ocular tissues and fluids remarkably well. However, it should be noted that pronounced conjunctival inflammation may lead to systemic absorption into the bloodstream.
It is used in ophthalmology for the treatment of conjunctivitis, blepharitis, and purulent corneal ulcers. The standard dosing regimen is instillation of 1–2 drops 4 to 6 times a day.
Tolerance is generally good, but high concentrations can cause local irritant effects: burning, itching, stinging, and lacrimation. In such cases, therapy is adjusted by switching to lower concentration solutions.
Silver-containing preparations
This group includes silver sulfadiazine and silver sulfathiazole. The presence of a silver atom fundamentally alters pharmacodynamics: upon dissociation, silver ions ($Ag^+$) are released, which bind to bacterial DNA. This provides a potent bactericidal effect.
The main distinguishing feature of these drugs is that their efficacy is not reduced in the presence of pus and tissue breakdown products. This is because the mechanism of action of silver ions does not depend on competition with para-aminobenzoic acid (PABA).
The spectrum of activity is broad and includes wound infection pathogens: staphylococci, Escherichia coli, Proteus, and Klebsiella. Activity against Pseudomonas aeruginosa (Pseudomonas aeruginosa) is of particular value.
They are applied topically as ointments for burn and wound infections, trophic ulcers, and pressure sores. Potential adverse effects include local allergic reactions, itching, and burning at the application site.
Combination drugs for the GI tract
The group includes sulfasalazine, salazopyridazine, and salazodimethoxine. Chemically, they are azo compounds consisting of a sulfonamide moiety and salicylic acid.
They are poorly absorbed in the small intestine, reaching the lower GI tract. In the large intestine, under the action of local microflora, hydrolysis (cleavage) of the compound into two active components occurs:
- 5-aminosalicylic acid — exerts a pronounced anti-inflammatory effect.
- Sulfonamide component — provides a local antibacterial effect.
Main indications: ulcerative colitis (UC), Crohn's disease, and baseline therapy for rheumatoid arthritis.
Sulfasalazine toxicity and group status
Sulfasalazine is taken orally (per os) and exhibits a wide spectrum of toxicity. Allergic reactions, dyspepsia, and a burning sensation in the rectum are possible. Hematologic adverse effects include leukopenia and agranulocytosis. The central nervous system may respond with ataxia, convulsions, tinnitus, and hallucinations. Cases of photosensitization and interstitial pneumonitis have also been described.
In modern clinical practice, the frequency of sulfonamide use is steadily declining. This is due to three factors:
- They are significantly inferior in antibacterial activity to modern antibiotics.
- They possess relatively high toxicity.
- Microorganisms rapidly develop resistance to them.
How to remember the action of sulfasalazine? Imagine a "double-bottom capsule": it passes through the small intestine in transit, and in the large intestine, bacteria "open" it, releasing the antibiotic (sulfonamide) and the anti-inflammatory agent (5-ASA).
Class and exam questions
Why do silver ointments work in purulent wounds while conventional sulfonamides do not?
Conventional sulfonamides compete with PABA, which is abundant in pus and destroyed tissues. Silver ions act differently—they bind directly to bacterial DNA, so pus does not interfere with their bactericidal effect.
What to do if sulfacetamide eye drops cause severe stinging and lacrimation?
Local irritation is typically associated with the use of high drug concentrations. To correct therapy, it is sufficient to switch to a solution with a lower active substance content.
How does sulfasalazine work in ulcerative colitis?
The drug is practically not absorbed in the small intestine. In the large intestine, microflora cleaves it into sulfonamide (suppressing pathogenic flora) and 5-aminosalicylic acid (relieving intestinal wall inflammation).
What else to study on this topic
- Mechanism of competitive antagonism between sulfonamides and para-aminobenzoic acid (PABA).
- Pharmacokinetics of sulfacetamide: conditions for systemic absorption.
- Effect of sulfasalazine on the hematopoietic system (mechanisms of agranulocytosis development).
- Causes and mechanisms of microbial resistance to sulfonamides.
Master the entire topic in the «Pharmacology» course
This is a summary. The course covers everything tested in classes and exams.
- Complete study guide on "Topical sulfonamides" and 5,304 other subject pages
- Assignments and quizzes after every topic — just like in a colloquium
- AI tutor answers questions on the topic anytime
- 116 video lessons on the subject
Other topics in the section "Antibacterial Chemotherapeutic Agents"
Free video lessons: pharmacologyShort lessons with study notes — no registration required.
Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.