No, there is no doxycycline 100 mcg (microgram) formulation available
Doxycycline is manufactured and prescribed in milligram (mg) doses, not microgram (mcg) doses—the standard formulations are 50 mg and 100 mg, which are 500 and 1000 times larger than 100 mcg, respectively. 1
Available Doxycycline Formulations
The FDA-approved doxycycline products include 1:
- Capsules: 50 mg and 100 mg
- Tablets: 100 mg
- Liquid suspension: 10 mg/mL (for FDA-approved products)
- Modified-release capsules: 40 mg (not recommended for most infections) 2
Standard Dosing
The confusion likely stems from the fact that 100 mg is the most common adult dose, used across multiple guidelines 3, 4:
- Acute Q fever: Doxycycline 100 mg twice daily for 14 days 3
- Skin and soft tissue infections (MRSA): 100 mg twice daily 4
- Sexually transmitted infections: 100 mg twice daily for 7 days for chlamydia 1, 5
- Doxycycline post-exposure prophylaxis (doxy-PEP): 200 mg as a single dose after sexual exposure 6
Clinical Context
If a prescription or order states "100 mcg," this is almost certainly an error and should be clarified immediately, as this would represent a 1000-fold underdose that would be therapeutically ineffective 1. The intended dose is likely 100 mg, which is the standard adult formulation for most indications 3, 4, 7, 2.
Pediatric Dosing Exception
For children, weight-based dosing is used (2.2 mg/kg per dose twice daily, maximum 100 mg per dose), but even these are measured in milligrams, not micrograms 3, 4.