chemistry

Sulfamethoxazole

Sulfamethoxazole is a chemistry topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Sulfamethoxazole rather than just read about it. In short: Sulfamethoxazole (SMZ or SMX) is an antibiotic. It is used for bacterial infections such as urinary tract infections, bronchitis, and prostatitis and is effective against both gram negative and positive bacteria such as Escherichia coli and Listeria monocytogenes.

Key takeaways

Sulfamethoxazole belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Sulfamethoxazole to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Sulfamethoxazole from memory before moving on to harder problems.

Reference excerpt

Sulfamethoxazole (SMZ or SMX) is an antibiotic. It is used for bacterial infections such as urinary tract infections, bronchitis, and prostatitis and is effective against both gram negative and positive bacteria such as Escherichia coli and Listeria monocytogenes. Common side effects include nausea, vomiting, loss of appetite, and skin rashes. It is a sulfonamide and bacteriostatic. It resembles a component of folic acid. It prevents folic acid synthesis in the bacteria that must synthesize their own folic acid. Mammalian cells, and some bacteria, do not synthesize but require preformed folic acid (vitamin B9); they are therefore insensitive to sulfamethoxazole. It was introduced to the United States in 1961. It is now mostly used in combination with trimethoprim (abbreviated SMX-TMP). The SMX-TMP combination is on the WHO Model List of Essential medicines as a first-choice treatment for urinary tract infections. Other names include: sulfamethalazole and sulfisomezole.

Side effects The most common side effects of sulfamethoxazole are gastrointestinal disturbances (nausea, vomiting, anorexia) and allergic skin reactions (such as rash and urticaria). There have been rare instances where severe adverse reactions have resulted in fatalities. These include Stevens–Johnson syndrome (SJS), toxic epidermal necrolysis, fulminant hepatic necrosis, agranulocytosis, aplastic anemia, and other blood dyscrasias. Allergic reactions to Sulfonamides have been shown to include the entire Gel-Coombs spectrum of hyperactivity reactions. Type 1 reactions include immunoglobulin E (IgE)-mediated reactions such as urticaria, angioedema, and anaphylaxis. In contrast, non-type 1 hypersensitivities are believed to be caused by metabolites of sulfonamides. Therefore, the liver and kidney are the determining factors of these other hypersensitivity reactions; alterations in kidney or liver functions may increase or decrease the frequencies of these reactions. One study has shown the allergic reaction rate to be about 3.0% over 359 courses of therapy. Of the allergic reactions, skin rashes, eosinophilia and drug fever were the most common, while serious reactions were less common. Sulfamethoxazole is contraindicated in people with a known hypersensitivity to trimethoprim or sulfonamides.

Mechanism of action

Sulfamethoxazole, a sulfanilamide, is a structural analog of para-aminobenzoic acid (PABA). They compete with PABA to bind to dihydropteroate synthetase and inhibit conversion of PABA and dihydropteroate diphosphate to dihydrofolic acid, or dihydrofolate. Inhibiting the production of dihydrofolate intermediate interferes with the normal bacterial synthesis of folic acid (folate). Folate is an essential metabolite for bacterial growth and replication because it is used in DNA synthesis, primarily at thymidylate and purine biosynthesis, and amino acids synthesis, including serine, glycine and methionine. Hence, blockage of folate production inhibits the folate-dependent metabolic processes for bacterial growth. Since it inhibits bacterial growth, sulfamethoxazole is considered a bacteriostatic antibiotic. Sulfonamides are selective against bacteria because they interfere with the synthesis of folate, a process which does not occur in humans. Humans do not synthesize folate, and must acquire it through diet.

Pharmacokinetics Absorption Sulfamethoxazole is well-absorbed when administered topically. It is rapidly absorbed when it is orally administered. Distribution Sulfamethoxazole distributes into most body tissues as well as into sputum, vaginal fluid, and middle ear fluid. It also crosses the placenta. About 70% of the drug is bound to plasma proteins. Its Tmax (or time to reach maximum drug concentration in plasma) occurs 1 to 4 hours after oral administration. The mean serum half-life of sulfamethoxazole is 10 hours. However, the half-life of the drug noticeably increases in people with creatinine clearance rates equal to or less than 30 mL/minute. A half-life of 22–50 hours has been reported for people with creatinine clearances of less than 10 mL/minute. Metabolism Sulfamethoxazole is metabolized in the human liver to at least 5 metabolites. These metabolites are the N4-acetyl-, N4-hydroxy-, 5-methylhydroxy-, N4-acetyl-5-methylhydroxy-sulfamethoxazole metabolites, and an N-glucuronide conjugate. The CYP2C9 enzyme is responsible for the formation of the N4-hydroxy metabolite. In vitro studies suggest sulfamethoxazole is not a substrate of the P-glycoprotein transporter. Excretion Sulfamethoxazole is primarily renally excreted via glomerular filtration and tubular secretion. About 20% of the sulfamethoxazole in urine is the unchanged drug, about 15–20% is the N-glucuronide conjugate, and about 50–70 % is the acetylated metabolite. Sulfamethoxazole is also excreted in human milk.

See also Sulfisoxazole List of cytochrome P450 modulators

Notes

External links

Illustrations

Worked examples

Example 1 — a first encounter with Sulfamethoxazole

Start with the simplest possible case. Write down what Sulfamethoxazole claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Sulfamethoxazole before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Sulfamethoxazole ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Sulfamethoxazole

In research: Sulfamethoxazole appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Sulfamethoxazole in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Sulfamethoxazole is common in secondary-school and first-year university syllabi. It links to neighbouring topics 4-Aminophenyl compounds, Aromatic amines, CYP2C9 inhibitors, so understanding it makes those chapters shorter.
In everyday life: Look for Sulfamethoxazole outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Sulfamethoxazole in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Sulfamethoxazole means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Sulfamethoxazole out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Sulfamethoxazole in simple terms?

Why does Sulfamethoxazole matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Sulfamethoxazole?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Sulfamethoxazole.