Sulfamethoxazole

Absorption

Sulfamethoxazole is rapidly absorbed following oral administration and has a bioavailability of 85-90%. The Tmax is approximately 1-4 hours following oral administration, and the Cmax at steady-state is 57.4 - 68.0 μg/mL.

Toxicity

The oral LD50 of sulfamethoxazole in mice and rats is 2300 mg/kg and 6200 mg/kg, respectively.
Signs or symptoms of sulfonamide overdose include anorexia, colic, nausea, vomiting, dizziness, headache, drowsiness, and unconsciousness. Less common symptoms may include pyrexia, hematuria, and crystalluria. Later manifestations of overdose may include blood dyscrasias and jaundice. Treatment should be symptomatic and supportive, and may include gastric lavage or forced emesis if applicable. Monitor patient lab work for evidence of blood dyscrasias or electrolyte imbalances.

Description

Like sulfisoxazole, this drug is effective in treating infections caused by streptococci, gonococci, pneumococci, staphylococci as well as colon bacillus. Unlike sulfisoxazole, only about 70% of it binds with proteins in the plasma after oral administration, and it diffuses mostly to tissues and tissue fluids. However, since it is removed much slower than sulfisoxazole, it does not require frequent administration and is also the drug of choice for many systemic infections. Moreover, it is an ingredient of a combined drug named bactrim, biseptol, and so on (which will be examined later on), which has a fixed correlation with trimethoprim. Synonyms of this drug are gantanol, sinomin, sulfisomezole, and others.

Chemical properties

solid

The Uses of Sulfamethoxazole

Sulfamethoxazole is an antibacterial drug and an antipneumocystis. Sulfonamide antibiotic that blocks the synthesis of dihydrofolic acid by inhibiting the enzyme dihydropteroate synthase.This compound is a contaminant of emerging concern (CECs).

Background

Sulfamethoxazole is a bacteriostatic sulfonamide antibiotic that interferes with folic acid synthesis in susceptible bacteria. It is generally given in combination with trimethoprim, which inhibits a sequential step in bacterial folic acid synthesis - these agents work synergistically to block two consecutive steps in the biosynthesis of nucleic acids and proteins which are necessary for bacterial growth and division, and using them in conjunction helps to slow the development of bacterial resistance. In this combination, sulfamethoxazole is useful for the treatment of a variety of bacterial infections, including those of the urinary, respiratory, and gastrointestinal tracts.

Indications

Sulfamethoxazole is indicated in combination with trimethoprim, in various formulations, 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.
In Canada, additional indications include the adjunctive treatment of cholera, treatment of bacillary dysentery, nocardiosis, and second-line treatment of brucellosis in combination with gentamicin or rifampicin.

Definition

ChEBI: An isoxazole (1,2-oxazole) compound having a methyl substituent at the 5-position and a 4-aminobenzenesulfonamido group at the 3-position.

brand name

Gantanol (Roche); Urobak (Shionogi).

Antimicrobial activity

The intrinsic activity is similar to that of sulfadiazine.

General Description

Crystals or white powder.

General Description

Sulfamethoxazole’s plasma half-life is 11 hours. Sulfamethoxazole is a sulfonamide drug closely relatedto sulfisoxazole in chemical structure and antimicrobial activity.It occurs as a tasteless, odorless, almost white crystallinepowder. The solubility of sulfamethoxazole in the pHrange of 5.5 to 7.4 is slightly lower than that of sulfisoxazole but higher than that of sulfadiazine, sulfamerazine, or sulfamethazine.Following oral administration, sulfamethoxazole is notabsorbed as completely or as rapidly as sulfisoxazole, andits peak blood level is only about 50% as high.

Air & Water Reactions

Insoluble in water.

Fire Hazard

Flash point data for Sulfamethoxazole are not available but Sulfamethoxazole is probably non-flammable.

Pharmaceutical Applications

This is the sulfonamide component of co-trimoxazole. It is slightly soluble in water.

Pharmacokinetics

Oral absorption： 85%
C_max 800 mg oral： c.50 mg/L after 3–6 h
Plasma half-life： 6–20 h
Volume of distribution： 12–18 L
Plasma protein binding： 65%
Penetration of extravascular sites, including the CSF, is good. It crosses the placenta and achieves levels in breast milk of about 10% of the simultaneous plasma concentration. It is extensively metabolized, but about 30% of the dose is excreted unchanged in urine so that high concentrations are achieved.

Clinical Use

Sulfamethoxazole is used only in combination with the diaminopyrimidine trimethoprim.

Side Effects

Sulfonamides, including sulfamethoxazole, have been implicated in hypersensitivity reactions - these agents should be discontinued at the first sign of a developing rash, as this may signal the start of a more severe reaction such as Stevens-Johnson syndrome or toxic epidermal necrolysis. Sulfamethoxazole treatment may contribute to folate deficiency and should, therefore, be used with caution in patients at a higher risk of developing a deficiency. Hemolysis has been observed in patients with glucose-6-phosphate dehydrogenase deficiency who are using sulfamethoxazole/trimethoprim. In addition, benign intracranial hypertension has been reported in children. Most side effects of co-trimoxazole are thought to be attributable to the sulfonamide component.

Safety Profile

Moderately toxic by ingestion and intraperitoneal routes. Questionable carcinogen with experimental tumorigenic data. When heated to decomposition it emits very toxic fumes of NOx and SOx.

Synthesis

Sulfamethoxazole, N1 -(5-methyl-3-isoxazolyl)sulfanilamide (33.1.20), is synthesized by a completely analogous scheme, except by using 3-amino-5-methylisoxazol as the heterocyclic component.

Metabolism

Sulfamethoxazole metabolism is mediated primarily by arylamine N-acetyltransferase (NAT) enzymes, which are responsible for acetylation of sulfamethoxazole at its N4 position. Sulfamethoxazole may also undergo oxidation at its C5 and N4 atoms, the latter of which is catalyzed by CYP2C9. Glucuronidation of the N4 atom, likely mediated by unspecified UGT enzymes, is an additional minor route of metabolism. None of the identified metabolites of sulfamethoxazole appear to carry antimicrobial activity.
The hydroxylamine metabolite of sulfamethoxazole, generated via oxidation by CYP2C9, may be further converted to a more reactive nitroso- metabolite.