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Septra (Trimethoprim / Sulfamethoxazole) - Drug Interactions, Contraindications, Overdosage, etc

 
 



DRUG INTERACTIONS

Drug Interactions:

In elderly patients concurrently receiving certain diuretics, primarily thiazides, an increased incidence of thrombocytopenia with purpura has been reported. In the literature, two cases of hyperkalemia in elderly patients have been reported after concomitant intake of trimethoprim/sulfamethoxazole and an angiotensin converting enzyme inhibitor.

It has been reported that SEPTRA may prolong the prothrombin time in patients who are receiving the anticoagulant warfarin. This interaction should be kept in mind when SEPTRA is given to patients already on anticoagulant therapy, and the coagulation time should be reassessed.

SEPTRA may inhibit the hepatic metabolism of phenytoin. SEPTRA, given at a common clinical dosage, increased the phenytoin half-life by 39% and decreased the phenytoin metabolic clearance rate by 27%. When administering these drugs concurrently, one should be alert for possible excessive phenytoin effect.

Sulfonamides can also displace methotrexate from plasma protein binding sites, thus increasing free methotrexate concentrations.

OVERDOSAGE

Acute:

The amount of a single dose of SEPTRA that is either associated with symptoms of overdosage or is likely to be life-threatening has not been reported. Signs and symptoms of overdosage reported with sulfonamides include anorexia, colic, nausea, vomiting, dizziness, headache, drowsiness, and unconsciousness. Pyrexia, hematuria, and crystalluria may be noted. Blood dyscrasias and jaundice are potential late manifestations of overdosage. Signs of acute overdosage with trimethoprim include nausea, vomiting, dizziness, headache, mental depression, confusion, and bone marrow depression.

General principles of treatment include the institution of gastric lavage or emesis; forcing oral fluids; and the administration of intravenous fluids if urine output is low and renal function is normal. Acidification of the urine will increase renal elimination of trimethoprim. The patient should be monitored with blood counts and appropriate blood chemistries, including electrolytes. If a significant blood dyscrasia or jaundice occurs, specific therapy should be instituted for these complications. Peritoneal dialysis is not effective and hemodialysis is only moderately effective in eliminating trimethoprim and sulfamethoxazole.

Chronic:

Use of SEPTRA at high doses and/or for extended periods of time may cause bone marrow depression manifested as thrombocytopenia, leukopenia, and/or megaloblastic anemia. If signs of bone marrow depression occur, the patient should be given leucovorin; 5 to 15 mg leucovorin daily has been recommended by some investigators.

CONTRAINDICATIONS

SEPTRA is contraindicated in patients with a known hypersensitivity to trimethoprim or sulfonamides and in patients with documented megaloblastic anemia due to folate deficiency. SEPTRA is also contraindicated in pregnant patients at term and in nursing mothers, because sulfonamides pass the placenta and are excreted in the milk and may cause kernicterus. SEPTRA is contraindicated in pediatric patients less than 2 months of age.

REFERENCES

  1. Kremers P, Duvivier J, Heusghem C. Pharmacokinetic studies of co-trimoxazole in man after single and repeated doses. J Clin Pharmacol. 1974;14:112-117.

  2. Kaplan SA, Weinfeld RE, Abruzzo CW, McFaden K, Jack ML, Weissman L. Pharmacokinetic profile of trimethoprim- sulfamethoxazole in man. J Infect Dis. 1973;128(suppl):S547-S555.

  3. Varoqaux O, et al. Pharmacokinetics of the trimethoprim-sulfamethoxazole combination in the elderly. Br J Clin Pharmacol. 1985; 20: 575-581.

  4. Antibiotic susceptibility discs; certification procedure. Federal Register. 1972;37:20527-20529.

  5. Bauer AW, Kirby WMM, Sherris JC, Turck M. Antibiotic susceptibility testing by standardized single disk method. Am J Clin Pathol. 1966;45:493-496.

  6. Brumfitt W, Pursell R. Trimethoprim-sulfamethoxazole in the treatment of bacteriuria in women. J Infect Dis. 1973;128 (suppl):S657-S663.

  7. Marinella MA. Trimethoprim – induced hyperkalemia: An analysis of reported cases. Gerontology 45: 209-212, 1999.

Rx Only.

Prescribing Information as of March 2007.

Distributed by: Monarch Pharmaceuticals, Inc., Bristol, TN 37620

(A wholly owned subsidiary of King Pharmaceuticals, Inc.)

Manufactured by: King Pharmaceuticals, Inc., Bristol, TN 37620

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