Medications and Drugs
Pharmacy Editor: Jay W. Marks, MD
GENERIC NAME: trimethoprim
BRAND NAMES: Trimpex, Proloprim, Primsol
DRUG CLASS AND MECHANISM: Trimethoprim is a synthetic (man-made)
antibiotic that interferes with the production of tetrahydrofolic acid, a
chemical that is necessary in order for bacteria and human cells to produce
proteins. Trimethoprim inhibits production of tetrahydrofolic acid by inhibiting
the enzyme responsible for making tetrahydrofolic acid from dihydrofolic acid.
Trimethoprim inhibits the bacterial enzyme more than the corresponding human
enzyme. Therefore, trimethoprim has less effect on the production of
tetrahydrofolic acid by humans. Trimethoprim is effective against a wide variety
of bacteria. Trimethoprim was first approved by the FDA in combination with
sulfamethoxazole (for
example, Bactrim, Septra) in 1973. It was approved as a
stand-alone drug in 1980.
PRESCRIPTION: Yes
GENERIC AVAILABLE: Yes
PREPARATIONS: Tablets: 100, and 200 mg. Solution: 50 mg/5 ml
STORAGE: Tablets should be kept at room temperature, 15-30 C (59-86
F).
PRESCRIBED FOR: Trimethoprim
is used for the treatment of urinary tract infections
, traveler's diarrhea, respiratory and middle ear infections,
and, when combined with either sulfamethoxazole or dapsone, for prevention and
treatment of Pneumocystis infections.
DOSING: The usual dose is 100 mg every 12 hours or 200 mg every 24
hours for 10 days. As with all antibiotics, it is important to complete the
entire course of trimethoprim even if symptoms improve early in therapy. Persons
with kidney diseases may need to receive lower doses. (Diseased kidneys may not
eliminate trimethoprim adequately from the body, and levels of trimethoprim may
increase in the body and lead to side effects.)
DRUG INTERACTIONS: Changes in one patient's mental status occurred
when a combination of trimethoprim and sulfamethoxazole was given with
amantadine (Symmetrel).
Blood levels of phenytoin (Dilantin) may
be increased by treatment with trimethoprim. This may lead to side effects
associated with phenytoin such as
dizziness, and reduced attention. Trimethoprim also may increase blood levels of
digoxin (Lanoxin) and warfarin (Coumadin) and lead to serious toxic effects.
Anemia, due to a reduction in folic acid, can occur in persons receiving
trimethoprim in combination with divalproex, valproic acid, methotrexate,
pyrimethamine, triamterene, or trimetrexate.
The combination of trimethoprim and cyclosporine can increase the risk of
kidney damage from cyclosporine.
When trimethoprim and dapsone are used together, increased blood
concentrations of both drugs can occur, sometimes with side effects that include
a toxic condition called methemoglobinemia.
Rifampin can increase the elimination of trimethoprim by the kidneys and may
reduce the effectiveness of trimethoprim.
PREGNANCY: Although there are
no human studies that have examined the effects of trimethoprim on the fetus,
animal studies have shown adverse effects. Therefore, the physician must weigh
the potential risks to the fetus against the potential benefits to the mother
when considering trimethoprim therapy for pregnant women
.
NURSING MOTHERS: Trimethoprim
is distributed into breast
milk in high
concentrations. Use of trimethoprim by mothers who are breast-feeding should be
avoided.
Report Problems to the Food and Drug Administration
You are encouraged to report negative side effects of prescription drugs to the FDA. Visit the FDA MedWatch website or call 1-800-FDA-1088.
- Drug Interactions - Learn about potential drug interactions you may be exposed to. Drug interactions can occur with prescription drugs, OTC medication, vitamins, herbs, and supplements.
- Liver Blood Tests - Learn about liver blood tests used to detect liver damage disease such as fatty liver, cirrhosis, hepatitis, Tylenol liver damage, and more. This includes measuring the aminotransferases enzymes (AST and ALT levels)
- Urinary Tract Infection (UTI In Adults) - Learn about urinary tract infection causes, symptoms, signs, diagnosis and treatment of UTIs in men and women. Antibiotics may be used to treat recurrent bladder infections.
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