In people with a creatinine clearance of about 75 mL/min, excretion by the kidney is about 40% in 72 hours. In people with a creatinine clearance below 10 mL/min, excretion can be as low as 1-5% in 72 hours.

The half-life of this drug is about 12 to 25 hours long and it takes roughly 5 half-lives to clear a substance from the body. That means it could take approximately 60 hours (2.5 days) to 125 hours (over 5 days) for the body to clear this antibiotic.

Doxycyline is likely detectable in your system for the following time frames:
– Blood/Serum: Peak serum concentrations in adults is roughly 2.6 mcg/mL, achieved after about 2 hours following a single 200 mg oral dose; after 24 hours, that dropped to 1.45 mcg/mL
– Breastmilk: The American Academy of Pediatrics recommends not providing breastfeeding within 24 hours of taking Flagyl, another antibiotic; while doxycyline can pass to breastmilk, it is not known what the long-term effects of this drug are on a breastfeeding infant.

(Numbers above are merely estimates, and may vary based on several factors, such as age and other medical conditions.)

Doxycycline is excreted in the urine and feces at high concentrations and in a biologically active form. In people with a creatinine clearance of about 75 mL/min, excretion by the kidney is about 40% in 72 hours. In people with a creatinine clearance below 10 mL/min excretion can be as low as 1-5% in 72 hours.

For most infections, symptoms start easing within a few days. However, it is essential that you finish the whole cycle as prescribed by your doctor.

If you lie down soon after you have taken doxycycline, the reflux of the drug can cause irritation to your throat.

No. Always follow your doctor’s indications.