Ceftriaxone
Ceftriaxone. Third-generation cephalosporin β-lactam — extended gram-negative + good gram-positive coverage. Once-daily IV/IM dosing… Intramuscular half-life 8.1 h.
Third-generation cephalosporin β-lactam — extended gram-negative + good gram-positive coverage. Once-daily IV/IM dosing makes it a workhorse for inpatient pneumonia, meningitis (CSF penetration), gonorrhea single-dose. Biliary > renal clearance — sludging in gallbladder.
PK: this record PASSES the two-route check — its citation genuinely dosed both intravenously and intramuscularly in a crossover — and its volume and intramuscular bioavailability are both verbatim. But the 8 versus 8.1 h split is a FABRICATED ROUTE DIFFERENCE: the paper reports one half-life for the crossover, and with a measured 100% intramuscular bioavailability there is no mechanism for a route difference anyway. BINDING IS SATURABLE ACROSS THE THERAPEUTIC RANGE, which the model cannot express: free fraction rises about fourfold, from 0.04 to 0.17, so total-drug volume runs 7.0 to 10.1 L and half-life 5.9 to 8.1 h between 0.15 and 3 g, while free-drug parameters stay dose-independent. The stored pair is therefore valid only at or below 1 g and will mis-predict at the 2 to 4 g meningitis regimens. ka 1.5 is dropped and is refuted by the paper own 1.4 h time to peak, which implies about 2.5 per hour.
Pharmacokinetics
- IV — t½ 8.1 h · F 100% · Vd 8.5 L
- Intramuscular — t½ 8.1 h · F 100% · Vd 8.5 L
Sources: PMID:3985603, PMID:7249794, PMID:6275779