Sulfamethoxazole

Sulfamethoxazole is a drug from the group of antibiotics. It is used for bacterial infections such as urinary tract infections, bronchitis and prostatitis and is effective against both gram-negative and positive bacteria.

Pharmacodynamics

Sulfamethoxazole is a sulfonamide that inhibits bacterial dihydrofolic acid synthesis because of its structural similarity to an endogenous substrate, para-aminobenzoic acid (PABA). Most bacteria meet their need for folic acid by synthesizing it from PABA. Sulfamethoxazole competitively inhibits dihydropteroate synthase, the enzyme responsible for bacterial conversion of PABA to dihydrofolic acid. Inhibition of this pathway prevents the synthesis of tetrahydrofolate and ultimately the synthesis of bacterial purines and DNA, resulting in a bacteriostatic effect.

Pharmacokinetics

Sulfamethoxazole is rapidly absorbed after oral administration and has a bioavailability of 85-90%. Sulfamethoxazole is approximately 70% bound to plasma proteins, mainly albumin. Metabolism occurs in the liver. Excretion is mainly by glomerular filtration and tubular secretion in the kidneys. Approximately 84.5% of a single oral dose of sulfamethoxazole is normally recovered in the urine within 72 hours. The mean serum half-life of sulfamethoxazole is 10 hours and may be increased in patients with severely impaired renal function.

Side effects

The most common side effects of sulfamethoxazole are gastrointestinal disturbances (nausea, vomiting, loss of appetite) and allergic skin reactions (such as rash and urticaria).

In rare cases, serious adverse effects occur. These include Stevens-Johnson syndrome, toxic epidermal necrolysis, fulminant hepatic necrosis, agranulocytosis, aplastic anemia, and other blood dyscrasias.

With the use of sulfonamides, there is a possibility of severe allergic reactions.

Toxicological Data

LD50 (mouse, oral): 2300 mg-kg-1