Trimethoprim

Description

Trimethoprim selectivity between bacterial and mammalian dihydrofolate reductases results from the subtle but significant architectural differences between these enzyme systems. Whereas the bacterial enzyme and the mammalian enzyme both efficiently catalyze the conversion of dihydrofolic acid to tetrahydrofolic acid, the bacterial enzyme is sensitive to inhibition by trimethoprim by up to 40,000-fold lower concentrations than the mouse enzyme is. This difference explains the useful selective toxicity of trimethoprim.

Chemical properties

Crystalline

Originator

Eusaprim,Wellcome,Italy,1970

The Uses of Trimethoprim

An antibacterial and inhibitor of formylation. Dihydrofolate reductase inhibitor with selectivity for the prokaryote enzyme.Trimethoprim is an antibiotic involved in the treatment of urinary tract infections, middle ear infections and traveler?s diarrhea. It is associated with sulfamethoxazole and interferes with the cellular metabolism of folic acid in the bacterial cell by blocking the biosynthesis of nucleotides. Furthermore, It is also used to treat and prevent Pneumocystis jiroveci pneumonia.

The Uses of Trimethoprim

anti-inflammatory

The Uses of Trimethoprim

An antibacterial agent which selectively inhibits dihydrofolate reductase.

Background

Trimethoprim is an antifolate antibacterial agent that inhibits bacterial dihydrofolate reductase (DHFR), a critical enzyme that catalyzes the formation of tetrahydrofolic acid (THF) - in doing so, it prevents the synthesis of bacterial DNA and ultimately continued bacterial survival. Trimethoprim is often used in combination with sulfamethoxazole due to their complementary and synergistic mechanisms but may be used as a monotherapy in the treatment and/or prophylaxis of urinary tract infections. It is structurally and chemically related to pyrimethamine, another antifolate antimicrobial used in the treatment of plasmodial infections.

Indications

As a monotherapy, trimethoprim is indicated for the treatment of acute episodes of uncomplicated urinary tract infections caused by susceptible bacteria, including E. coli., K. pneumoniae, Enterobacter spp., P. mirabilis, and coagulase-negative Staphylococcus species. In various formulations in combination with sulfamethoxazole, trimethoprim is indicated for the following infections caused by bacteria with documented susceptibility: urinary tract infections, acute otitis media in pediatric patients (when clinically indicated), acute exacerbations of chronic bronchitis in adults, enteritis caused by susceptible Shigella, prophylaxis and treatment of Pneumocystis jiroveci pneumonia, and travelers' diarrhea caused by enterotoxigenic E. coli.
Trimethoprim is available as an ophthalmic solution in combination with polymyxin B for the treatment of acute bacterial conjunctivitis, blepharitis, and blepharoconjunctivitis caused by susceptible bacteria.

Definition

ChEBI: Trimethoprim is an aminopyrimidine antibiotic whose structure consists of pyrimidine 2,4-diamine and 1,2,3-trimethoxybenzene moieties linked by a methylene bridge. It has a role as an EC 1.5.1.3 (dihydrofolate reductase) inhibitor, a xenobiotic, an environmental contaminant, a drug allergen, an antibacterial drug and a diuretic. It is a member of methoxybenzenes and an aminopyrimidine.

Manufacturing Process

6 grams (0.26 mol) sodium was dissolved in 300 ml methanol under stirring and refluxing. 47.5 grams (0.55 mol) β-methoxypropionitrile and 98 grams (0.5 mol) 3,4,5-trimethoxybenzaldehyde were added and the mixture refluxed gently for 4 hours. The mixture was then chilled and 150 ml of water was added. The product crystallized rapidly. Crystallization was allowed to proceed at 5° to 10°C under stirring for 1 hour. The product was filtered by suction and washed on the filter with 200 ml of 60% ice cold methanol. The crude material was air-dried and used for further steps without purification. It melted at 78° to 80°C. A pure sample, recrystallized from methanol, melted at 82°C. The yield of 3,4,5-trimethoxy-2'-methoxymethylcinnamonitrile was 92 grams, corresponding to 70% of the theory.
19 grams (0.83 mol) sodium was dissolved in 300 ml methanol, 106 grams of 3,4,5-trimethoxy-2'-methoxymethylcinnamonitrile was added and the mixture gently refluxed for 24 hours. The solution, which had turned brown, was poured into 1 liter of water and the precipitated oil extracted repeatedly with benzene. The combined benzene layers (500 to 700 ml) were washed 3 times with 500 ml of water, the benzene removed by evaporation in a vacuum from a water bath, and the brown residual oil distilled in vacuo, boiling point 215° to 225°C/11 mm. The clear, viscous oil, 3,4,5-trimethoxy-2'-cyano_x0002_dihydrocinnamaldehyde dimethyl acetal, weighed 83 grams (71% of the theory), and showed a nD23 = 1.5230. It solidified upon standing. A sample recrystallized from methanol melted at 69° to 70°C and showed a strong melting point depression with the starting material; nD25 = 1.5190. 31.5 grams (0.107 mol) 3,4,5-trimethoxy-2'-cyano-dihydrocinnamaldehyde dimethyl acetal was refluxed with methanolic guanidine solution (200 ml containing 0.25 mol of guanidine) for 2 hours. The methanol completely distilled off under stirring, finally from a bath of 110° to 120°C until the residue solidified completely to a yellowish crystalline mass. After allowing to cool, it was slurried with 100 ml of water and collected by vacuum filtration and dried. The yield of 2,4-diamino-5-(3,4,5-trimethoxybenzyl)pyrimidine amounted to 28 grams (91% of the theory). The material showed the correct melting point of 199° to 200°C and was, however, yellowish discolored. 20 grams of the above product was added to 30 ml of 3 N aqueous sulfuric acid at 60°C under stirring. The solution was chilled under stirring to 5° to 10°C. The crystalline sulfate was collected by vacuum filtration and washed on the filter twice with 10 ml of cold 3 N aqueous sulfuric acid each time. From the filtrate there was recovered 1.3 grams (6.5%) of discolored material melting at 195° to 196°C and which can be added to subsequent purification batches.
The sulfate on the filter was dissolved in 200 ml of hot water, the solution charcoaled hot, and the product precipitated from the clear colorless filtrate by the gradual addition of a solution of 20 grams of sodium hydroxide in 40 ml of water under chilling. The precipitate was filtered by suction and washed thoroughly with water on the filter. The white material, 17.5 grams (88%) showed the correct melting point of 200° to 201°C, according to US Patent 3,341,541.

brand name

Proloprim (Monarch); Trimpex (Roche).

Therapeutic Function

Antibacterial (urinary)

Toxicity

The oral LD50 in mice and rats is 2764 mg/kg and >5300 mg/kg, respectively.
Prescribing information for trimethoprim states that signs of overdose may be evident following ingestion of doses >1 gram, and may include nausea, vomiting, dizziness, headaches, mental depression, confusion, and bone marrow depression. Treatment should consist of general supportive measures and gastric lavage, if applicable. Urinary acidification may increase renal elimination of trimethoprim. Hemodialysis is only moderately effective in eliminating trimethoprim and peritoneal dialysis is of no benefit.

Antimicrobial activity

Trimethoprim has a broad spectrum of antimicrobial activity. It is 20–100 times more active than sulfamethoxazole with respect to most bacterial forms. Trimethoprim is active with respect to Gram-positive, aerobic bacteria such as Staphylococcus aureus, Staphylococcus epidermidis, and various types of Streptococcus and Listeria monocytogenes. Trimethoprim is inferior to sulfonamides against forms of Nocardia. It is active with respect to Gram-negative, aerobic bacteria such as most E. coli, Enterobacter, Proteus, Klebsiella, Providencia, Morganella, Serratia marcescens, Citrobacter, Salmonella, Shigella, Yersinia enterocolitica that are sensitive to trimethoprim. Trimethoprim is also active with respect to Legionella, Acinetobacter, Vibrio, Aeromonas, Pseudomonas maltophila, P. cepacia, although P. aeruginosa is resistant to trimethoprim.

General Description

Odorless white powder. Bitter taste.

Air & Water Reactions

Insoluble in water.

Reactivity Profile

Trimethoprim readily forms salts with acids. .

Fire Hazard

Flash point data for Trimethoprim are not available. Trimethoprim is probably combustible.

Biochem/physiol Actions

Inhibits the synthesis of tetrahydrofolate by procaryote specific dihydrofolate reductase (DHFR).

Mechanism of action

Haemophilus influenzae and H. ducreyi are sensitive to trimethoprim. Pathogenic Neisseria (meningococci and gonococci) and Branhamella catarrhalis are moderately resistant to trimethoprim, although they are very sensitive to a combination of trimethoprim and sulfamethoxazole. Anaerobic bacteria in general are resistant to trimethoprim, although a combination of trimethoprim-sulfamethoxazole does have an effect on them. Pneumocystis carinii is also sensitive to that combination.
Bacterial resistance to trimethoprim can originate because of a number of reasons: inability of the drug to penetrate through the membrane (P. aeruginosa); the presence of dihydrofolate reductase that is not sensitive to inhibition by trimethoprim; overproduction of dihydrofolate reductase and mutation expressed as thyminic dependence, when the organism requires exogenic thymine for synthesizing DNA, i.e. bypassing metabolic blockage caused by trimethoprim.
Resistance to a combination of trimethoprim-sulfamethoxazole is always less frequent than when any of these drugs is used separately. This combination of drugs, which is known by the commercial names cotrimoxazole, bactrim, biseptol, sulfatrim, and many others, is used for treating infections of the respiratory tract, infections of the urinary tract, gastric infections, surgical infections, enteritis, meningitis, and other diseases.

Pharmacokinetics

Trimethoprim exerts its antimicrobial effects by inhibiting an essential step in the synthesis of bacterial nucleic acids and proteins. It has shown activity against several species of gram-negative bacteria, as well as coagulase-negative Staphylococcus species. Resistance to trimethoprim may arise via a variety of mechanisms, including alterations to the bacterial cell wall, overproduction of dihydrofolate reductase, or production of resistant dihydrofolate reductase. Rarely, trimethoprim can precipitate the development of blood disorders (e.g. thrombocytopenia, leukopenia, etc.) which may be preceded by symptoms such as sore throat, fever, pallor, and or purpura - patients should be monitored closely for the development of these symptoms throught the course of therapy.
As antimicrobial susceptibility patterns are geographically distinct, local antibiograms should be consulted to ensure adequate coverage of relevant pathogens prior to use.

Clinical Use

Trimethoprim (5-[(3,4,5-trimethoxyphenyl)methyl]-2,4-pyrimidinediamine or 2,4-diamino-5-(3,4,5-trimethoxybenzyl)pyrimidine) is closely related to several antimalarialsbut does not have good antimalarial activity by itself; it is,however, a potent antibacterial. Originally introduced incombination with sulfamethoxazole, it is now available as asingle agent.
Approved by the FDA in 1980, trimethoprim as a singleagent is used only for the treatment of uncomplicatedurinary tract infections. The argument for trimethoprim asa single agent was summarized in 1979 by Wormser andDeutsch. They point out that several studies comparingtrimethoprim with TMP–SMX for the treatment ofchronic urinary tract infections found no statistically relevantdifference between the two courses of therapy.The concern is that when used as a single agent, bacterianow susceptible to trimethoprim will rapidly developresistance. In combination with a sulfonamide, however,the bacteria will be less likely to do so. That is, they willnot survive long enough to easily develop resistance toboth drugs.

Synthesis

Trimethoprim, 2,4-diamino-5-(3,4,5-trimethoxybenzyl)pyrimidine (33.1. 51), is synthesized in various ways. The first scheme of synthesis begins with ethyl ester of 3,4,5-trimethoxydehydrocinnamic acid, which is formylated with ethyl formate using sodium as a base to make an enol of the semialdehyde 3,4,5-trimethoxybenzylmalonic ester (33.1.49), which undergoes a heterocyclization reaction with guanidine to make 2-amino- 4-hydroxy-5-(3,4,5-trimethoxybenzyl)pyrimidine (33.1.50). Subsequent replacement of the hydroxyl group in the resulting product with chlorine using phosphorous oxychloride and then with an amino group using ammonia gives the desired trimethoprim.

All of the other syntheses begin with 3,4,5-trimethoxybenzaldehyde. According to one of them, condensation of 3,4,5-trimethoxybenzaldehyde with 3-ethoxy- or 3-anilinopropionitrile gives the corresponding benzylidene derivative (33.1.52), which upon direct reaction with guanidine gives trimethoprim.

Trimethoprim has also been synthesized by condensing 3,4,5-trimethoxybenzaldehyde with malonic acid dinitrile in a Knoevenagel reaction, which forms the derivative (33.1.53), which is partially reduced to the enamine (33.1.54) by hydrogen using a palladium on carbon catalyst, which upon being reacted with guanidine is transformed into trimethoprim.

Finally, trimethoprim can be synthesized in a manner that also uses a Knoevenagel condensation of 3,4,5-trimethoxybenzaldehyde as the first step, but this time with ethyl cyanoacetate, which gives an ylidene derivative (33.1.55). The double bond in this product is reduced by hydrogen over a palladium on carbon catalyst, giving 3,4,5-trimethoxybenzylcyanoacetic ester (33.1.56). Reacting this in a heterocyclization reaction with guanidine gives the desired trimethoprim.

Drug interactions

Potentially hazardous interactions with other drugs
Anti-arrhythmics: increased risk of ventricular arrhythmias with amiodarone - avoid; concentration of procainamide increased.
Antiepileptics: antifolate effect and concentration of fosphenytoin and phenytoin increased.
Antimalarials: increased risk of antifolate effect with pyrimethamine.
Ciclosporin: increased risk of nephrotoxicity; concentration of ciclosporin reduced by IV trimethoprim.
Cytotoxics: increased risk of haematological toxicity with azathioprine, methotrexate and mercaptopurine; antifolate effect of methotrexate increased.
Tacrolimus: possible increased risk of nephrotoxicity.

Metabolism

Trimethoprim undergoes oxidative metabolism to a number of metabolites, the most abundant of which are the demethylated 3'- and 4'- metabolites, accounting for approximately 65% and 25% of the total metabolite formation, respectively. Minor products include N-oxide metabolites (<5%) and benzylic metabolites in even smaller quantities. The parent drug is considered to be the therapeutically active form.
The majority of trimethoprim biotransformation appears to involve CYP2C9 and CYP3A4 enzymes, with CYP1A2 contributing to a lesser extent.

Metabolism

About 10 to 20
% of trimethoprim is metabolised in the liver and small amounts are excreted in the faeces via the bile, but most, about 40 to 60
% of a dose, is excreted in urine, mainly as unchanged drug.
Trimethoprim is excreted mainly by the kidneys through glomerular filtration and tubular secretion.

Absorption

Steady-state concentrations are achieved after approximately 3 days of repeat administration. Average peak serum concentrations of approximately 1 μg/mL (Cmax) are achieved within 1 to 4 hours (Tmax) following the administration of a single 100mg dose. Trimethoprim appears to follow first-order pharmacokinetics, as a single 200mg dose results in serum concentrations approximately double that of a 100mg dose. The steady-state AUC of orally administered trimethoprim is approximately 30 mg/L·h.