Barbiturates once enjoyed vast popularity as sedatives and sleep inducing agents. Over time their side effects led to more caution and at present these agents are seldom prescribed for insomnia and sleep disorders. Some of the risks associated with barbiturates use include:-
Barbiturates are primarily sedatives and they induce sleep. Since this is their primary pharmacological effect, some amount of excessive drowsiness is commonly seen especially in case of overdose.
This sleepiness may persist over the next day as well. This may manifest as a hangover sleepiness that makes driving and operating heavy machinery on the next day morning a hazard. There is impaired psychomotor function and increased pain perception that may persist over the next day.
Dependence and tolerance to barbiturates
Over long term use dependence develops to barbiturates. This means that patients are unable to sleep without taking barbiturates.
Tolerance is an associated phenomenon. This means over long term use sleep is difficult without increasing the dose. Finally the highest dose range of the drugs fails to produce sleep but may lead to other side effects.
Depression of respiration
Barbiturates have a narrow therapeutic range. This means these agents lead to side effects when they cross the normal dose range. Since this range is a narrow one there is a risk of over dose.
Barbiturates in high doses cause depression of the respiratory centre of the brain leading to decreased drive for respiration. In severe cases of over dosage there is a complete suppression of respiration leading to respiratory failure.
Peripheral Nervous System depression
The peripheral nervous system is also depressed with over dosage of barbiturates. There is a decreased excitation of neuronal receptors that is enhanced by several other concomitant agents and drugs.
There is decreased cardiac contractility and cardiac output. This means the heart pumps blood with less power of contraction. There is also a decrease in blood flow to the brain.
Action on enzymes of the liver
There are several enzymes present in the liver that function in metabolizing various drugs. Barbiturates enhance the action of these enzymes. This is called enzyme induction.
Enzyme induction leads to increased metabolism of certain medications concomitantly taken along with barbiturates. This means the duration of action of these drugs is markedly reduced when taken alongside barbiturates.
Some of the drugs whose metabolism and effectiveness is affected by barbiturate use include anti-seizure drugs like phenytoin and carbamazepine, antibiotics like rifampicin etc.
Action on the renal function
There is decreased flow rate (glomerular flow rate) into the kidneys and decreased blood flow to the kidneys due to use of barbiturates. This results in lowered blood pressure and decreased urine volume
Barbiturate risks in older patients and pregnant women
The risk of side effects of barbiturates is higher in older patients and among pregnant women. This is because with age the ability to excrete and eliminate the drugs from the system decreases.
Elderly over the age of 65 are at higher risk of experiencing adverse effects of barbiturates and also are at risk of drug dependence and accidental overdose.
If taken during pregnancy these agents pass through the mother’s blood into the fetus via the placenta. The baby may be born with congenital abnormalities.
Reviewed by April Cashin-Garbutt, BA Hons (Cantab)