01Which labelled uses are once daily?
Usual maintenance: 100 mg daily. Malaria prophylaxis: 100 mg daily with the travel dates already described. The alternate chlamydia row: 200 mg once daily for 7 days.
200 mg once daily is a named 7-day alternate, not a new habit for acne adjunct. This site's lock remains 100 mg delayed-release.
02Why does day one split 100 mg every 12 hours?
Because the usual adult dosage is 200 mg on the first day, given as 100 mg every 12 hours. That is a load, then a step down to 100 mg daily for many uses.
Daily maintenance can be one swallow or 50 mg every 12 hours. This vault still talks in 100 mg delayed-release units. A 50 mg split is only if that strength is what was written.
03Does switching to MPC change once versus twice?
MPC replacement is 120 mg for 100 mg Doryx. The usual MPC pattern mirrors the same day-one split and daily maintenance in 120 mg units. It is still a different product.
Do not take 100 mg DR twice and 120 mg MPC once on the same day to invent a match. Pick the written product. Ordinary tablets and MPC are not silent substitutes.
04Who chooses once versus twice on an unlisted infection?
The clinician, after naming a labelled use or accepting that the file has no day count. Severe acne adjunct has no frequency of its own beyond the usual adult pattern the writer applies.
If the order is silent on timing, ask before guessing. Guessing twice daily on a malaria pack, or once daily on a 60-day anthrax pack, is how calendars break. Duration backup: how long the course runs.
05When does 100 mg every 12 hours continue after day one?
In more severe infections, particularly chronic urinary-tract infections. Uncomplicated C. trachomatis, gonococcal infection except anorectal infection in men, and NGU from U. urealyticum keep 100 mg twice daily for 7 days. Syphilis rows that allow doxycycline keep twice daily for 2 or 4 weeks. Anthrax post-exposure keeps twice daily for 60 days. Epididymo-orchitis from C. trachomatis is twice daily for at least 10 days.
Those are named rows. Do not keep twice-daily dosing because a leftover blister looks even.
06If you miss one swallow on a twice-daily row, do you switch to once daily?
No. A miss does not rewrite the indication. Do not double. The miss page is a missed Doryx 100 mg tablet.
If nausea is the reason people want once daily, gastric irritation can take food or milk. That is comfort, not a frequency change the patient votes in.