antibioticsbooks

chapter 3 Pharmacokinetics 25
Table 3–1
Examples of Absorption for Different Oral Antibiotics
Drug
Bioavailability
Typical
Intravenous Dose
Typical Oral
Dose
Drugs with High Bioavailability and Similar Intravenous–Oral Doses
Metronidazole 95–100% 500 mg IV q8h 500 mg PO q8h
Levofloxacin 95–100% 500–750 mg IV q8 500–750 mg PO
daily
Linezolid 95–100% 600 mg IV q8h 600 mg PO q12h
Fluconazole 95–100% 200–400 mg IV
daily
200–400 mg PO
daily
Doxycycline 95–100% 100 mg IV q12h 100 mg PO q12h
Ciprofloxacin ~80% 400 mg IV q12h 500 mg PO q12h
Drugs with High Bioavailability but Different Intravenous–Oral Doses
Aminopenicillins ~90% Ampicillin: 1–2 g
IV q4–6h
First-gen
cephalosporins
~90% Cefazolin: 1–2 g
IV q8h
Amoxicillin: 500
mg–1 g PO TID
Cephalexin: 500 mg
PO QID
Drugs with Low Bioavailability and Different Intravenous–Oral Doses
Cefuroxime ~40% 750 mg IV q8h 500 mg PO BID
Acyclovir ~25% 5 mg/kg IV q8h 400 mg PO TID
doses, and those with limited oral bioavailability.
Some oral antibiotics have almost zero bioavailability
and take advantage of this clinically to
eradicate pathogens in the GI tract, where they
achieve much higher concentrations than they
would if given intravenously.
It is important to consider factors that can
affect the bioavailability of antibiotics. Three factors
that can substantially influence absorption
are food, gastric acidity, and chelating agents.
Some antibiotics are better absorbed with food
and some without, while for most antibiotics the
presence or absence of food has minimal effect.