CO-TRIMEXAZOLE SUSPENSION

Source of information: Drugbank (External Link). Last updated on: 3^rd July 18
*Trade Name used in the content below may not be the same as the HSA-registered product.

Active Ingredient / Synonyms

2,4-Diamino-5-(3,4,5-trimethoxybenzyl)pyrimidine | 5-[(3,4,5-Trimethoxyphenyl)methyl]-2,4-pyrimidinediamine | Trimethoprim | Triméthoprime | Trimethoprimum | Trimetoprima | Trimethoprim |

Description

A pyrimidine inhibitor of dihydrofolate reductase, it is an antibacterial related to pyrimethamine. The interference with folic acid metabolism may cause a depression of hematopoiesis. It is potentiated by sulfonamides and the trimethoprim-sulfamethoxazole combination is the form most often used. It is sometimes used alone as an antimalarial. Trimethoprim resistance has been reported. [PubChem]

Indication

For the treatment of urinary tract infections, uncomplicated pyelonephritis (with sulfamethoxazole) and mild acute prostatitis. May be used as pericoital (with sulfamethoxazole) or continuous prophylaxis in females with recurrent cystitis. May be used as an alternative to treat asymptomatic bacteriuria during pregnancy (only before the last 6 weeks of pregnancy). Other uses include: alternative agent in respiratory tract infections (otitis, sinusitus, bronchitis and pneumonia), treatment of Pneumocystis jirovecii pneumonia (acute or prophylaxis), Nocardia infections, and traveller's diarrhea.

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 affinity for bacterial dihydrofolate reductase is several thousand times greater than its affinity for human dihydrofolate reductase. Sulfamethoxazole inhibits dihydrofolate synthetase (aka dihydropteroate synthetase), an enzyme involved further upstream in the same pathway. Trimethoprim and sulfamethoxazole are commonly used in combination due to their synergistic effects. This drug combination also reduces the development of resistance that is seen when either drug is used alone.

Pharmacodynamics

Trimethoprim is a pyrimidine analogue that disrupts folate synthesis, an essential part of the thymidine synthesis pathway. Inhibition of the enzyme starves the bacteria of nucleotides necessary for DNA replication.The drug, therefore, exhibits bactericidal activity.

Pharmacokinetics

Absorption:

Readily and almost completely absorbed in the GI tract with peak serum concentrations attained 1-4 hours after oral administration. Widely distributed to tissues and fluids including kidney, lung, seminal fluid, aqueous humour, middle ear fluid, sputum, vaginal secretions, bile, bone and CSF.

Distribution:

Not Available

Metabolism:

Hepatic metabolism to oxide and hydroxylated metabolites.

Elimination:

Ten to twenty percent of trimethoprim is metabolized, primarily in the liver; the remainder is excreted unchanged in the urine. After oral administration, 50% to 60% of trimethoprim is excreted in the urine within 24 hours, approximately 80% of this being unmetabolized trimethoprim. Trimethoprim also passes the placental barrier and is excreted in human milk.

Half-life

8-11 hours in adults with normal renal function

Clearance

Not Available

Toxicity

LD₅₀=4850 (orally in mice)