Alprazolam (Xanax, Xanor) and
lorazepam (Ativan) are very similar in terms of efficacy and therapeutic effects. Both of these benzodiazepines (BZDs) are very potent -- one mg of lorazepam is equipotent to 10 mg of
diazepam (Valium), whereas 0.5 mg of alprazolam is equipotent to 10 mg of diazepam (in other words, on a gram for gram basis, alprazolam is 20 times as potent as diazepam, whereas lorazepam is 10 times as potent as diazepam). Both alprazolam and lorazepam are 1,4-benzodiazepines (so-called "classical" BZDs). Most BZDs are 1,4-benzodiazepines, and the numerous drugs in this class (including alprazolam, nordazepam, lorazepam, nitrazepam, oxazepam, flurazepam, halazepam, lormetazepam, loprazolam, midazolam, flunitrazepam, prazepam, estazolam, etc.) have various combinations of sedative, hypnotic, amnestic, anxiolytic, anticonvulsant, and muscle-relaxant properties. The 1,5-benzodiazepines, such as clobazam (Frisium, Urbanol) and triflubazam are less sedating, and clobazam has a much longer half-life than lorazepam or alprazolam (clobazam is prescribed in many countries).
Although lorazepam and alprazolam have short half-lives, they differ markedly in terms of their metabolism. The principal metabolite of lorazepam is the glucuronide, which is excreted in the urine as lorazepam glucuronide. Alprazolam, on the other hand, is hydroxylated in the liver to form hydroxyalprazolam, which is much less pharmacologically active than the parent compound. Thus, alprazolam should not be taken together with drugs that burden the P450 cytochrome pathway (e.g., ritonavir); lorazepam is much safer when administered together with such drugs.
Lorazepam is a unique BZD in that it is a powerful anti-emetic; it is therefore used frequently as an adjunctive drug in chemotherapy.
Lorazepam and alprazolam have a relatively high potential for abuse, because of their potency and the possibility of interdose rebound effects. Both drugs pack a powerful and sharp punch; diazepam, on the other hand, has a slower onset of action and a much longer half-life (its primary metabolite, nordazepam, has a half-life of between 30 and 200 hours).
I hope that this information is useful.
PHILIP CHANDLER
Alprazolam to Lorazepam 
Alprazolam versus lorazepam... 
Linear Mode
