Ranitidine
Ranitidine. H2 receptor antagonist — historically the highest-volume PO H2 blocker. Withdrawn 2020 due to NDMA contamination across the supply… Oral half-life 2.3 h.
H2 receptor antagonist — historically the highest-volume PO H2 blocker. Withdrawn 2020 due to NDMA contamination across the supply chain. Less CYP DDI than cimetidine but more than famotidine.
PK: the stored 3 h was wrong twice over and is a DIGIT COLLISION — its own paper reports 2.3 h oral and 1.7 h intravenous, and separately "a second peak at 3 +/- 0 h". The half-life is genuinely route-specific here and the paper gives the mechanism: more extensive biotransformation and biliary excretion after oral dosing, with renal recovery of 79% intravenously against 27% orally. ABSORPTION IS BIMODAL — "a first peak at 1.1 h and a second peak at 3 h" — so no single first-order rate is admissible at any value, and ka 1 is dropped rather than replaced. V 96 L and F 0.60 are BOTH verbatim and the volume is intravenous-derived, so that pairing is correct and is left alone. THE EFFECT-COMPARTMENT VALUE IS REMOVED FOR A STRUCTURAL REASON: the drug reaches its gastric pH target at 20-40 minutes while the plasma first peak is at 1.1 h, so the effect PRECEDES plasma, and an effect compartment can only delay effect, never advance it. Its note also said "oral" where the source studied EFFERVESCENT tablets, whose published selling point is faster onset.
Pharmacokinetics
- Oral — t½ 2.3 h · F 60% · Vd 96 L
- IV — t½ 1.7 h · F 100% · Vd 96 L
Sources: PMID:6125204, PMID:9663842, PMID:9205741, PMID:6329583