Sulfamethoxazole-Trimethoprim

Sulfamethoxazole-Trimethoprim

Indication

• There are few indications for the use of co-trimoxazole in the neonate; Sulfamethoxazole-Trimethoprim is contraindicated during the first 7 days of life due to risk of kernicterus at lower levels of bilirubin
• Its use is limited to those unusual situations where culture and sensitivity results dictate (E.G. Pneumocystis carinii).

Pharmacology

• Sulfamethoxazole-Trimethoprim is a combination product which contains two anti-infectives, trimethoprim (TMP) and sulfamethoxazole (SMZ) in a 1:5 ratio
• Sulfamethoxazole-Trimethoprim acts by inhibiting sequential steps in the synthesis of tetrahydrofolic acid, an important cofactor in DNA synthesis
• Well absorbed (90 to 100%) following oral administration
• In adults, approximately 80% of trimethoprim and 20% of sulfamethoxazole are excreted unchanged in the urine

Side Effects

• Sulfamethazole weakly displaces bilirubin from albumin; do NOT administer co-trimoxazole to infants with hyperbilirubinemia
• GI adverse effects and sensitivity skin reactions are the most frequent (approximately 3.5% of patients)
• Rare hematological reactions
• Local reactions (pain, inflammation and rarely thrombophlebitis)

Contraindications

• Patients with documented megaloblastic anemia secondary to folate deficiency
• Patients with suspected glucose-6-phosphate-dehydrogenase (G-6-PD) deficiency
• Use within first 7 days of life

Dose

The available IV solution must be diluted at least 15 times prior to administration and given by slow infusion over at least 30 minutes

It should be noted by the physician that the manufacturer states that Sulfamethoxazole-Trimethoprim must be diluted at least 15 times before administration. Consideration should be given to the use of a third generation cephalosporin before Sulfamethoxazole-Trimethoprim is used. Sulfamethoxazole-Trimethoprim should not be used in infants less than 28 days old. It is recommended that this guideline be adhered to. The physician should be aware of the increased fluid intake and adjust the fluid management (including tpn) of the infant accordingly

Sample Calculation for IV administration. Order reads:

• 6mg TMP and 30 mg SMZ IV q12h

Desired dose:

Therefore the volume of drug to be administered is 0.375 mL

Diluted 15 times:

• 0.375 mL x 15 = 5.625 mL

Total volume:

• 0.375 mL (Drug) + 5.25 mL (Diluent) = 5.625 mL (Round off to 5.6 mL) to be given by slow infusion over 30 minutes. 

Remember: whenever a drug volume exceeds 2 mL, additional extension tubing must be added.

Available

• The pediatric Suspension contains per mL: 
  • 8 mg TMP, 40 mg SMX
• 5 mL multidose vial for injection, with benzyl alcohol present, contains per mL: 
  • 16 mg TMP, 80 mg SMX