Trimethoprim-sulfamethoxazoleNursing considerations

Side effects by what to assess

Sources: [1][2][3][4][5]

INR (prothrombin time)

Why

Prolonged prothrombin time in patients on warfarin

When

When started in a patient on warfarin

Normal

INR 0.8 to 1.1 when not on a blood thinner. On warfarin, the usual target is 2.0 to 3.0.

Sources: [1][2]

Potassium

Why

Trimethoprim-induced hyperkalemia

When

Closely with high doses, renal insufficiency, potassium disorders, or potassium-raising drugs

Act on

Stop for a significant electrolyte abnormality

Normal

3.7 to 5.2 mEq/L.

Sources: [1][2][3]

Serum creatinine

Why

Renal insufficiency, crystalluria, and dose adjustment

When

During therapy, with urinalysis, especially in renal impairment

Act on

Halve the dose at creatinine clearance 15 to 30; not recommended below 15

Normal

0.7 to 1.3 mg/dL in men and 0.5 to 0.95 mg/dL in women.

Sources: [1][2][3]

White blood cell count

Why

Agranulocytosis, leukopenia, and other blood dyscrasias

When

Frequently during therapy

Act on

Stop for a drop in any formed blood element

Normal

4,500 to 11,000 per microliter.

Sources: [1][2]

High-alert status

Trimethoprim-sulfamethoxazole is not on the ISMP acute care high-alert list.

Sources: [1]

Narrow therapeutic index

The label does not describe a narrow therapeutic index or direct dosing by measured blood levels of the drug.

Sources: [1]

Boxed warning

None on the current label.

Sources: [1]

Antidote or reversal

No specific antidote. With normal kidneys and low urine output, give IV fluids; acidifying the urine speeds trimethoprim elimination. Hemodialysis is only moderately effective. For bone marrow depression from high-dose or prolonged use, give leucovorin 5 to 15 mg daily until blood counts recover.

Sources: [1]

Patient teaching

• Stop taking it and call your provider for rash, sore throat, fever, joint pain, cough, chest pain, trouble breathing, unusual bruising, or yellow skin or eyes
• Drink plenty of fluids to prevent crystals and kidney stones
• Finish the full course; it treats bacterial infections, not colds
• Call your provider for watery or bloody diarrhea, even months after the last dose
• Tell your provider if you take warfarin, phenytoin, methotrexate, or diabetes pills

Sources: [1][2]

Sound-alike and look-alike names

None listed in the ISMP list of confused drug names.

Sources: [1]

Adult dose

Urinary tract infection

1 DS tablet (800 mg/160 mg) or 2 regular tablets every 12 hours for 10 to 14 days.

Shigellosis or traveler's diarrhea

1 DS tablet every 12 hours for 5 days.

Chronic bronchitis exacerbation

1 DS tablet every 12 hours for 14 days.

Pneumocystis pneumonia treatment

Trimethoprim 15 to 20 mg/kg/day with sulfamethoxazole 75 to 100 mg/kg/day, split every 6 hours, for 14 to 21 days.

Pneumocystis prophylaxis

1 DS tablet daily.

Sources: [1]

Renal adjustment

Creatinine clearance above 30: usual regimen. 15 to 30: half the usual regimen. Below 15: not recommended. Half-lives of both components rise in severe renal impairment.

Sources: [1][2]

Hepatic adjustment

Contraindicated with marked hepatic damage; avoid in impaired hepatic function. Fulminant hepatic necrosis has occurred.

Sources: [1][2][3]

Mechanism

Sulfamethoxazole competes with para-aminobenzoic acid (PABA) to block bacterial dihydrofolic acid synthesis, and trimethoprim reversibly inhibits dihydrofolate reductase, blocking the next step to tetrahydrofolic acid. Together they block two consecutive steps in nucleic acid and protein synthesis, and resistance develops more slowly than with either drug alone. Both are cleared mainly by the kidneys, with half-lives of about 10 hours (sulfamethoxazole) and 8 to 10 hours (trimethoprim). Trimethoprim inhibits CYP2C8 and OCT2; sulfamethoxazole inhibits CYP2C9.

Sources: [1][2][3]