B.i.d. stands for the Latin phrase “bis in die,” which means twice a day. You’ll most often see it on a prescription label or in a doctor’s instructions telling you to take a medication two times per day, typically spaced about 12 hours apart.
Where You’ll See B.I.D.
Doctors and pharmacists use b.i.d. as shorthand when writing prescriptions. A prescription might read something like “amoxicillin 500 mg b.i.d.,” meaning you’d take one dose in the morning and another in the evening. The abbreviation saves space on prescription pads and electronic orders, though your pharmacy label will usually translate it into plain English like “take one tablet twice daily.”
FDA regulations require that all prescription drug labeling include clear information about frequency and duration of administration. For over-the-counter drugs, the label must include plain-language directions for use. So even if your doctor writes “b.i.d.” on your prescription, the bottle you pick up from the pharmacy should spell it out in words you can easily understand.
Why Spacing Matters
Twice daily doesn’t just mean “at some point, take it twice.” The goal is to keep a steady level of the drug in your bloodstream throughout the day. For antibiotics, pain medications, seizure drugs, and blood pressure medications, evenly spaced doses work noticeably better than two doses taken close together. A common approach is to pair doses with your morning and evening routines, roughly 12 hours apart. Taking both doses at breakfast and lunch, for instance, would leave a long overnight gap where the drug level drops too low to be effective.
Other Dosing Abbreviations
B.i.d. belongs to a family of Latin-based shorthand that describes how often you take a medication. Here are the most common ones:
- q.d. (quaque die): once a day
- b.i.d. (bis in die): twice a day
- t.i.d. (ter in die): three times a day
- q.i.d. (quater in die): four times a day
- q.o.d. (quoque alternis die): every other day
As the frequency goes up, the intervals between doses get shorter. T.i.d. means roughly every 8 hours, and q.i.d. means roughly every 6 hours. These aren’t rigid to the minute, but the spacing principle is the same: keep the drug working consistently rather than spiking and crashing.
What to Do if You Miss a Dose
For most twice-daily medications, the standard guidance is straightforward: take the missed dose as soon as you remember, as long as your next scheduled dose isn’t due within a few hours. If it is, skip the missed one and return to your regular schedule. Don’t double up to make up for it.
Some drug classes have stricter rules. Seizure medications taken twice daily, for example, follow a tighter window. A forgotten dose can generally be taken if it’s within 6 hours of when it was due. If more than 6 hours have passed, you’d skip it and take the next dose at the normal time. The specific window depends on the medication, so the instructions that come with your prescription are worth reading carefully.
Why Prescriptions Still Use Latin
Medical Latin abbreviations date back centuries, when Latin was the shared language of science across Europe. They stuck around because they’re compact and universal across languages. A doctor in any country recognizes “b.i.d.” regardless of what language they speak day to day. That said, these abbreviations can cause confusion for patients and even lead to errors when handwriting is unclear. The abbreviation “q.d.” (once daily), for instance, has been misread as “q.i.d.” (four times daily), a potentially dangerous mix-up. Many hospitals and health systems now encourage writing out “twice daily” in full on patient-facing documents to avoid exactly this kind of mistake.