The rates of oral absorption depend on the lipophilicity of the drugs. Most sedative-hypnotics are highly lipid soluble and exert their actions fast.

Redistribution is when highly lipid soluble drugs distribute to the brain, heart and kidneys very fast and then redistributes to the muscle and fat tissue.

Hepatic metabolism accounts for the clearance of all benzodiazepines.Most benzodiazepines undergo microsomal oxidation (phase 1 reaction), including dealkylationand hydroxylation catalyzed by cytochrome P450 enzymes.The metabolites are subsequently conjugated (phase 2 reaction) to form glucuronides that are excreted in the urine. Manyphase 1 metabolites of benzodiazepines are pharmacologically active.

The metabolism of several commonly used benzodiazepines including diazepam, midazolam and triazolam is affected by inhibitors and inducers of cytochrome P450 isozymes, because these benzodiazepines are mainly metabolized by these enzymes and inhibition of these isozyme may cause prolonged action of theses drugs.

BD not dependent on cytochrome P450 enzyme metabolism:

• oxaxepam
• lorazepam
• temazepam
• lormetazepam

the drugs are preferred in patients with compromised cytochrome P450 activity.

Anterograde amnesia is inability to remember events occurring during the drug’s duration of action, and this can be caused by benzodiazepines.

Sedative-hypnotics decreases the time it takes to fall asleep, it increases the duration of NREM sleep while decreasing the duration of REM sleep where rapid eye movement takes place, it also decreases your deep sleep stage a.k.a your slow wave sleep.

The barbiturates thiopental and methohexital are very lipid soluble and penetrates the brain tissue rapidly following IV administration and this favors their use for induction in general anesthesia.

Benzodiazepines including clonazepam, nitrazepam, lorazepam and diazepam are sufficiently selective to be useful in the management of seizures.

Carbamates and BD exert an inhibitory effect on polysynaptic reflexes and internuncial transmission and at high dosages depresses the neuromuscular junction.

At hypnotic doses in healthy patients the effects of sedative hypnotics are comparable to changes during natural sleep, they can produce significant pulmonary depression in patients with pulmonary disease.

BD used as anxiolytics:

• Alprazolam
• Bromazepam
• Diazepam
• Chlordiazepoxide
• Clobazam
• Flurazepam
• Lorazepam
• Oxazepam

BD used as hypnotics:

• Loprazolam
• Lormetazaepam
• Midazolam
• Nitrazepam
• Temazepam
• Triazolam

Preperations in  which barbiturates are used for anxiolytic/hypnotic purposes:

•  Adco-phenobarbitone vitalet
• Lethyl
• Sedabarb
•  
• Prazepam