The following adverse reactions have been observed with the use of barbiturates in hospitalized patients. Because such patients may be less aware of certain of the milder adverse effects of barbiturates, the incidence of these reactions may be somewhat higher in fully ambulatory patients.
More than 1 in 100 patients. The most common adverse reaction, somnolence,
is estimated to occur at a rate of 1 to 3 patients per 100.
Less than 1 in 100 patients. The most common adverse reactions estimated
to occur at a rate of less than 1 in 100 patients listed below, grouped by organ
system, and by decreasing order of occurrence are:
Central nervous system/psychiatric: Agitation, confusion, hyperkinesia,
ataxia, CNS depression, nightmares, nervousness, psychiatric disturbance, hallucinations,
insomnia, anxiety, dizziness, thinking abnormality.
Respiratory: Hypoventilation, apnea.
Cardiovascular: Bradycardia, hypotension, syncope.
Gastrointestinal: Nausea, vomiting, constipation.
Other reported reactions:Headache, hypersensitivity (angioedema, skin
rashes, exfoliative dermatitis), fever, liver damage. a
Drug Abuse And Dependence
Abuse and dependence
Abuse and addiction are separate and distinct from physical dependence and
tolerance. Abuse is characterized by misuse of the drug for non-medical purposes,
often in combination with other psychoactive substances. Physical dependence
is a state of adaptation that is manifested by a specific withdrawal syndrome
that can be produced by abrupt cessation, rapid dose reduction, decreasin g
blood level of the drug and/or administration of an antagonist. Tolerance is
a state of adaptation in which exposure to a drug induces changes that result
in a diminution of one or more of the drug's effects over time. Tolerance may
occur to both the desired and undesired effects of drugs and may develop at
different rates for different effects.
Addiction is a primary, chronic, neurobiological disease with genetic, psychosocial,
and environmental factors influencing its development and manifestations. It
is characterized by behaviors that include one or more of the following: impaired
control over drug use, compulsive use, continued use despite harm, and craving.
Drug addiction is a treatable disease, utilizing a multidisciplinary approach,
but relapse is common.
Barbiturates may be habit-forming. Tolerance, psychological dependence, and physical dependence may occur especially following prolonged use of high doses of barbiturates. Daily administration in excess of 400 milligrams (mg) of pentobarbital or secobarbital for approximately 90 days is likely to produce some degree of physical dependence. A dosage of from 600 to 800 mg taken for at least 35 days is sufficient to produce withdrawal seizures. The average daily dose for the barbiturate addict is usually about 1.5 grams. As tolerance to barbiturates develops, the amount needed to maintain the same level of intoxication increases; tolerance to a fatal dosage, however, does not increase more than two-fold. As this occurs, the margin between an intoxicating dosage and a fatal dosage becomes smaller.
Symptoms of acute intoxication with barbiturates include unsteady gait, slurred speech, and sustained nystagmus. Mental signs of chronic intoxication include confusion, poor judgment, irritability, insomnia, and somatic complaints. Symptoms of barbiturate dependence are similar to those of chronic alcoholism.
If an individual appears to be intoxicated with alcohol to a degree that is radically disproportionate to the amount of alcohol in his or her blood, the use of barbiturates should be suspected. The lethal dose of a barbiturate is far less if alcohol is also ingested.
The symptoms of barbiturate withdrawal can be severe and may cause death. Minor withdrawal symptoms may appear 8 to 12 hours after the last dose of a barbiturate. These symptoms usually appear in the following order: anxiety, muscle twitching, tremor of hands and fingers, progressive weakness, dizziness, distortion in visual perception, nausea, vomiting, insomnia, and orthostatic hypotension. Major withdrawal symptoms (convulsions and delirium) may occur within 16 hours and last up to 5 days after abrupt cessation of these drugs. Intensity of withdrawal symptoms gradually declines over a period of approximately 15 days.
Drug dependence to barbiturates arises from repeated administration of a barbiturate or agent with barbiturate-like effect on a continuous basis, generally in amounts exceeding therapeutic dose levels. The characteristics of drug dependence to barbiturates include: (a) a strong desire or need to continue taking the drug; (b) a tendency to increase the dose; (c) a psychic dependence on the effects of the drug related to subjective and individual appreciation for those effects; and (d) a physical dependence on the effects of the drug requiring its presence for maintenance of homeostasis and resulting in a definite, characteristic, and self-limited abstinence syndrome when the drug is withdrawn.
Treatment of barbiturate dependence consists of cautious and gradual withdrawal of the drug. Barbiturate-dependent patients can be withdrawn by using a number of different withdrawal regimens. In all cases, withdrawal takes an extended period of time. One method involves initiating treatment at the patient's regular dosage level, in 3 to 4 divided doses, and decreasing the daily dose by 10 percent if tolerated by the patient.
Infants physically dependent on barbiturates may be given phenobarbital 3 to 10 mg/kg/day. After withdrawal symptoms (hyperactivity, disturbed sleep, tremors, hyperreflexia) are relieved, the dosage of phenobarbital should be gradually decreased and completely withdrawn over a 2- week period.