Jan 10, - Ativan peak duration - The most quality drugs manufactured by the infuture.eu flagyl mg how do w/the onset peak hr. Lorazepam, sold under the brand name Ativan among others, is a benzodiazepine medication. When given by injection onset of effects is between one and thirty minutes and effects last for up to a day. .. This explains why one lorazepam dose, despite its shorter serum half-life, has more prolonged peak effects than an Onset of action?: ?1–5 min (IV), 15–30 min (IM). Oct 10, - peak plasma levels are reached within minutes, whereas following . of lorazepam with probenecid may result in a more rapid onset or.