Are there any interactions between Bactrim DS (trimethoprim/sulfamethoxazole) and paromomycin?

Drug Interaction Between Bactrim DS and Paromomycin

There are no clinically significant documented drug interactions between Bactrim DS (trimethoprim/sulfamethoxazole) and paromomycin. These medications can be safely co-administered when clinically indicated.

Pharmacological Basis for Safety

Paromomycin's Minimal Systemic Absorption

• Paromomycin is an aminoglycoside antibiotic that is poorly absorbed from the gastrointestinal tract when given orally, resulting in minimal systemic exposure and therefore minimal potential for systemic drug interactions 1, 2.
• The drug acts primarily within the intestinal lumen for parasitic infections (amebiasis, cryptosporidiosis) or bacterial overgrowth conditions 3, 4.

Bactrim DS Interaction Profile

• The primary drug interactions of concern with trimethoprim/sulfamethoxazole involve drugs metabolized by cytochrome P450 enzymes, antifolate medications (like methotrexate), and drugs affecting renal elimination 5.
• Paromomycin does not fall into any of these categories 1, 2.

Key Interaction Considerations for Bactrim DS (Not Related to Paromomycin)

While not relevant to paromomycin specifically, be aware that Bactrim DS has important interactions with:

High-Risk Drug Combinations

• Methotrexate: Co-trimoxazole causes bone marrow suppression and increased antifolate effects; this combination should be avoided 5.
• Warfarin: Potentiation of anticoagulant activity requiring INR monitoring 5.
• Drugs prolonging QT interval: Sulfamethoxazole can cause QT prolongation and torsades de pointes 5.
• Digoxin: Trimethoprim may increase serum digoxin levels, particularly in elderly patients 5.

Monitoring Recommendations When Using Bactrim DS

Regardless of co-administration with paromomycin, standard monitoring for Bactrim DS includes:

• Complete blood count to detect hematologic toxicity (anemia, thrombocytopenia, granulocytopenia) 5.
• Serum potassium levels, especially in patients taking ACE inhibitors, ARBs, or those at risk for hyperkalemia 5.
• Renal function monitoring, as both trimethoprim and sulfamethoxazole are renally eliminated 1, 2.
• Immediate discontinuation if rash develops, given risk of Stevens-Johnson syndrome or toxic epidermal necrolysis 5.

Special Populations Requiring Caution

Elderly Patients

• Increased susceptibility to adverse effects from trimethoprim/sulfamethoxazole, including bone marrow suppression and electrolyte disturbances 5, 6.
• More frequent monitoring is warranted in this population 6.

Renal Impairment

• Dose adjustment of Bactrim DS is required when creatinine clearance falls below 30 mL/min 1, 2.
• Trimethoprim and sulfamethoxazole metabolites accumulate in renal dysfunction, potentially leading to toxicity 1.

Clinical Bottom Line

Proceed with co-administration of Bactrim DS and paromomycin without concern for direct drug-drug interaction. Focus your monitoring efforts on the well-established adverse effects of each individual agent rather than interaction-related complications. The lack of systemic absorption of oral paromomycin eliminates the pharmacokinetic basis for interaction with systemically active Bactrim DS 1, 3, 2.