chemistry

Trimethoprim

Trimethoprim 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 Trimethoprim rather than just read about it. In short: Trimethoprim (TMP) is an antibiotic used mainly in the treatment of bladder infections. Other uses include for middle ear infections and travellers' diarrhoea.

Key takeaways

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

Reference excerpt

Trimethoprim (TMP) is an antibiotic used mainly in the treatment of bladder infections. Other uses include for middle ear infections and travellers' diarrhoea. With sulfamethoxazole or dapsone it may be used for Pneumocystis pneumonia in people with HIV/AIDS. It is taken orally (swallowed by mouth). Common side effects include nausea, changes in taste, and rash. Rarely it may result in blood problems such as not enough platelets or white blood cells. Trimethoprim may cause sun sensitivity. There is evidence of potential harm during pregnancy in some animals but not humans. It works by blocking folate metabolism via dihydrofolate reductase in some bacteria, preventing creation of bacterial DNA and RNA and leading to bacterial cell death. Trimethoprim was first used in 1962. It is on the World Health Organization's List of Essential Medicines. It is available as a generic medication.

Medical uses It is primarily used in the treatment of urinary tract infections, although it may be used against any susceptible aerobic bacterial species. It may also be used to treat and prevent Pneumocystis jirovecii pneumonia. It is generally not recommended for the treatment of anaerobic infections such as Clostridioides difficile colitis (the leading cause of antibiotic-induced diarrhea). Trimethoprim has been used in trials to treat retinitis. Resistance to trimethoprim is increasing, but it is still a first-line antibiotic in many countries.

Spectrum of susceptibility Cultures and susceptibility tests should be done to make sure bacteria are treated by trimethoprim.

Escherichia coli Proteus mirabilis Klebsiella pneumoniae Enterobacter species Coagulase-negative Staphylococcus species, including S. saprophyticus Streptococcus pneumoniae Haemophilus influenzae

Side effects

Common Nauseas Change in taste Vomiting Diarrhoea Rashes Sun sensitivity Itchiness

Rare Can cause thrombocytopenia (low levels of platelets) by lowering folic acid levels; this may also cause megaloblastic anemia. Trimethoprim antagonizes the epithelial sodium channel in the distal tubule, thus acting like amiloride. This can cause increased potassium levels in the body (hyperkalemia). Can compete with creatinine for secretion into the renal tubule. This can cause an artificial rise in the serum creatinine. Use in EHEC infections may lead to an increase in expression of Shiga toxin.

Contraindications Known hypersensitivity to trimethoprim History of megaloblastic anemia due to folate deficiency It may be involved in a reaction similar to disulfiram when alcohol is consumed after it is used, in particular when used in combination with sulfamethoxazole.

Pregnancy Based on the studies that show that trimethoprim crosses the placenta and can affect folate metabolism, there has been growing evidence of the risk of structural birth defects associated with trimethoprim, especially during the first trimester of pregnancy. The trophoblasts in the early fetus are sensitive to changes in the folate cycle. A 2013 study found a doubling in the risk of miscarriage in women exposed to trimethoprim in the early pregnancy.

Mechanism of action

Trimethoprim binds to dihydrofolate reductase and inhibits the reduction of dihydrofolic acid (DHF) to tetrahydrofolic acid (THF). THF is an essential precursor in the thymidine synthesis pathway and interference with this pathway inhibits bacterial DNA synthesis. Trimethoprim's inhibitory activity for bacterial dihydrofolate reductase is sixty thousand times greater than for human dihydrofolate reductase. Sulfamethoxazole inhibits dihydropteroate synthase, an enzyme involved further upstream in the same pathway. Trimethoprim and sulfamethoxazole are commonly used in combination due to possible synergistic effects, and reduced development of resistance. This benefit has been questioned.

History Trimethoprim was first used in 1962. In 1972, it was used as a prophylactic treatment for urinary tract infections in Finland. Its name is derived from trimethyloxy-pyrimidine.

References

Illustrations

Worked examples

Example 1 — a first encounter with Trimethoprim

Start with the simplest possible case. Write down what Trimethoprim 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 Trimethoprim 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 Trimethoprim 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 Trimethoprim

In research: Trimethoprim 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 Trimethoprim 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: Trimethoprim is common in secondary-school and first-year university syllabi. It links to neighbouring topics Antibiotics, Antimetabolites, Aromatic amines, so understanding it makes those chapters shorter.
In everyday life: Look for Trimethoprim 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 Trimethoprim in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Trimethoprim 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 Trimethoprim out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Trimethoprim in simple terms?

Trimethoprim (TMP) is an antibiotic used mainly in the treatment of bladder infections. Other uses include for middle ear infections and travellers' diarrhoea.

Why does Trimethoprim 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 Trimethoprim?

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 Trimethoprim.