The major difference between diazepam and alprazolam is their half-lives. This is a measure of how long their action lasts in the body. Diazepam has a longer half-life than alprazolam, meaning that it affects the body for a longer time, while alprazolam exerts its effect for a shorter interval. Diazepam is referred to as long-acting and alprazolam as intermediate-acting.
Belonging to the same class, diazepam and alprazolam are both benzodiazepine drugs. They are sedative hypnotics used mainly to treat anxiety in the short term. Benzodiazepines may also be used for pre-operative sedation, management of alcohol withdrawal, treatment of some seizure disorders and as a muscle relaxant. Long term use of either drug is discouraged due to their addictive potential, both psychologically and physically.
Diazepam and alprazolam share a common mechanism of action on the central nervous system (CNS). They affect the GABA receptors in the brain, causing an anxiolytic, or calming effect. The therapeutic doses of these medications differ, however, to get the same effect. For alprazolam, 0.5 mg is approximately equivalent to 5 mg of diazepam.
Both diazepam and alprazolam are metabolized, or broken down in the body, by the hepatic microsomal enzyme system in the liver. This may make them more susceptible to drug interactions with other medications, especially those also metabolized by the liver. Any concomitant medications should be discussed with the prescribing medical practitioner. Some of the other drugs in the benzodiazepine class, like lorazepam and oxazepam, are not metabolized in the liver.
Benzodiazepines are available in most countries by prescription only, due to their highly addictive nature. Diazepam is available as an oral or injectable product. Alprazolam is available only as an oral product, in both normal release and sustained release forms. The dose and duration of both diazepam and alprazolam will be determined by the prescribing doctor, according to the condition being treated. The lowest effective dose for the shortest duration will be given.
Due to the fact that diazepam is available as an injectable and alprazolam is not, diazepam may be used in acute situations. These include treatment of status epilepticus, where a rapid onset of action is required. Absorption via the injectable route tends to be quicker than oral administration and may be preferred in life-threatening situations.
Patients addicted to benzodiazepines who try to stop using them may experience withdrawal symptoms. The withdrawal symptoms will appear more quickly with the intermediate-acting alprazolam than the longer-acting diazepam. Diazepam is sometimes used during the withdrawal period, allowing a lessening of withdrawal symptoms. Diazepam is then withdrawn slowly. Withdrawal from benzodiazepines should be done only under close medical supervision.