Guidelines for Prescribing Ivermectin and Trimethoprim
There is no FDA-approved combination medication called "Ivectrim" containing ivermectin and trimethoprim together. Ivermectin and trimethoprim are separate medications with different indications, dosing regimens, and safety profiles.
Ivermectin Prescribing Guidelines
FDA-Approved Indications
- Ivermectin is FDA-approved for the treatment of strongyloidiasis and onchocerciasis at specific doses 1
- For strongyloidiasis: Single oral dose of 200 mcg/kg of body weight 1
- For onchocerciasis: Single oral dose of 150 mcg/kg of body weight 1
Dosing Considerations
- Patients should take tablets on an empty stomach with water 1
- For strongyloidiasis treatment, follow-up stool examinations should be performed to verify eradication of infection 1
- For onchocerciasis, retreatment may be considered at intervals as short as 3 months 1
Safety Considerations
- Common side effects include dizziness, nausea, fever, headache, muscle/joint pain, and skin reactions 2
- When used for onchocerciasis, patients may experience a Mazzotti reaction (tender lymphadenopathy, headache, bone/joint pain, fever, urticaria, and asthma) 2
- Bioavailability increases 2.5 times when taken with high-fat food 2
- Patients with severe liver disease may be at higher risk for toxicity 3
Trimethoprim Prescribing Guidelines
FDA-Approved Indications
- Trimethoprim is typically prescribed as trimethoprim-sulfamethoxazole (TMP-SMZ) 4
- FDA-approved indications for TMP-SMZ include urinary tract infections, shigellosis, acute otitis media, acute exacerbations of chronic bronchitis, and Pneumocystis carinii pneumonia 4
Dosing Considerations
- For adults with urinary tract infections: 1 double-strength tablet or 2 regular-strength tablets (400 mg/80 mg) every 12 hours for 10-14 days 4
- For children: 40 mg/kg sulfamethoxazole and 8 mg/kg trimethoprim per 24 hours, divided into two doses every 12 hours 4
- Dose adjustment required for patients with impaired renal function 4
Safety Considerations
- Contraindicated in pregnant women, nursing mothers, and infants aged <2 months due to risk of kernicterus 5
- Common adverse effects include gastrointestinal symptoms, hypersensitivity skin reactions, and rarely Stevens-Johnson syndrome 5
- Should be used with caution in patients with impaired hepatic and renal functions, folate deficiency, and blood dyscrasias 5
Off-Label Uses
Acne Vulgaris
- TMP-SMZ is sometimes used off-label for acne treatment, but is not FDA-approved for this indication 5
- Use as monotherapy should be avoided 5
- Rare severe allergic reactions (Stevens-Johnson syndrome) make it potentially undesirable if alternative treatments exist 5
Head Lice
- Ivermectin has been used off-label for head lice treatment 5
- Not FDA-approved for this indication 5
- Should not be used for children who weigh less than 15 kg due to risk of crossing the blood-brain barrier 5
COVID-19
- Current evidence does not support the routine use of ivermectin for COVID-19 treatment or prevention 6
- The Cochrane review found very low to low-certainty evidence regarding efficacy and safety of ivermectin for COVID-19 6
- Self-medication with ivermectin for COVID-19 is not recommended 7
Important Precautions
- Never combine these medications without specific medical indication 5
- TMP-SMZ should not be administered to pregnant women, nursing mothers, or infants aged <2 months 5
- Ivermectin should be used with caution in patients with liver disease 3
- Monitor for drug interactions, especially with TMP-SMZ which interacts with methotrexate, oral anticoagulants, antidiabetic agents, and other medications 5
Common Pitfalls to Avoid
- Prescribing TMP-SMZ for patients with known sulfa allergies 5
- Using ivermectin at doses higher than FDA-approved for parasitic infections 3
- Failing to adjust TMP-SMZ dosing in patients with renal impairment 4
- Prescribing either medication as monotherapy for conditions requiring combination therapy 5
- Self-medication or using these medications for unproven indications 7