Barbiturate Pharmacology

Here are some basic definitions.  You must know the differences between all of these as these are the therapeutic uses for barbiturates.

General Anesthetic: Total loss of sensation.  Requires the highest dose.

Hypnotic: Induces sleep

Sedative: Agent that quiets excitement, by calming mind and body

Anticonvulsant: Stops or decreases incidents of seizures (inhibits convulsions) at doses below sedative/hypnotic doses so it has the lowest relative dose.

Barbiturate Pharmacology

Barbiturates have been around for a long time and we still don’t know which receptors they hit.  We know it works on the CNS, and the initial effect is excitement for the short and fasting acting ones due to that surge.  But then the depressant effect comes in.

Barbiturates cause sleep induction but the sleep is not normal due to decreased REM sleep which is the most important phase of sleep (even though there’s a lot of activity going on).  With barbiturates, since you sleep without the REM sleep, prolonged use will lead to irritability, restlessness and nightmares.  For this reason it should not be used habitually for over 7 days.

Barbiturates have hyperalgesia properties, which is the opposite of analgesia (where you don’t feel pain).  In other words, if you do have pain, barbiturates heighten the pain.

All barbiturates have anesthetic, hypnotic, sedative and anticonvulsant properties, but each one is generally approved for only one specific use.

Barbiturates are easy to spot because they end with -barbital.  There is one general anesthetic that’s unusual because it doesn’t end with barbital, and that’s thiopental.  Thiopental is a very fast acting general anesthetic.  It puts the person out and they wake up quickly which is great in an ambulatory setting because they could just go home afterwards.  The problem is it’s a poor analgesic so this wouldn’t be great for a dentists office.

What happens when a drug causes a problem such as hyperalgesia?  We add another drug.  That will always be the answer.  So in this case, for example, a dentist may use nitrous oxide (laughing gas).

Barbiturate’s have a hepatic function:  Enzyme induction (metabolic induction) occurs which speeds up the metabolism of other agents.

Dependence:   They can be both physically and psychologically dependent.

Withdrawal: They cannot go cold-turkey on a barbiturate due to the risk of seizures.

Barbiturate examples

Hypnotics

Pentobarbital (Nembutal) – inj, p.o., p.r.

Secobarbital (Seconal) – inj., p.o.

Anticonvulsant

Phenobarbital (Luminal) – inj., p.o.

Anesthetic

Thiopental (Pentothal) – inj.