McKenna's Pharmacology for Nursing, 2e

311

C H A P T E R 2 0 Anxiolytic and hypnotic agents

TABLE 20.2

DRUGS IN FOCUS Barbiturate used as anxiolytic-hypnotic

Drug name

Dosage/route

Usual indications

Adult: 30–120 mg/day PO, slow IV or IM Paediatric: 1–6 mg/kg PO b.d. or t.d.s. or 1–3 mg/kg/day by slow IV or IM

Sedative–hypnotic; control of seizures Onset: 10–60 minutes Duration: 4–16 hours Special considerations: Taper gradually after long-term use; give IV slowly; monitor injection sites

Phenobarbitone sodium (generic)

Contraindications and cautions Contraindications to barbiturates include allergy to any barbiturate and a previous history of addiction to sedative/hypnotic drugs because the barbiturates are more addicting than most other anxiolytics. Other con- traindications are latent or manifest porphyria, which may be exacerbated ; marked hepatic impairment or nephritis, which may alter the metabolism and excre- tion of these drugs ; and respiratory distress or severe respiratory dysfunction, which could be exacerbated by the CNS depression caused by these drugs. Preg- nancy is a contraindication because of potential adverse effects on the fetus ; congenital abnormalities have been reported with barbiturate use. Use with caution in people with acute or chronic pain because barbiturates can cause paradoxical excite- ment, masking other symptoms ; with seizure disorders because abrupt withdrawal of a barbiturate can precipi- tate status epilepticus ; and with chronic hepatic, cardiac or respiratory diseases, which could be exacerbated by the depressive effects of these drugs. Care should be taken with breastfeeding women because of the poten- tial for adverse effects on the infant. Adverse effects As previously stated, the adverse effects caused by barbi- turates are more severe than those associated with other, newer sedatives/hypnotics. For this reason, barbiturates are no longer considered the mainstay for the treatment of anxiety. In addition, the development of physical tol- erance and psychological dependence is more likely with the barbiturates than with other anxiolytics. The most common adverse effects are related to general CNS depression. CNS effects may include drows- iness, somnolence, lethargy, ataxia, vertigo, a feeling of a “hangover”, thinking abnormalities, paradoxical excite- ment, anxiety and hallucinations. GI signs and symptoms such as nausea, vomiting, constipation, diarrhoea and epigastric pain may occur. Associated cardiovascular effects may include bradycardia, hypotension (par- ticularly with IV administration) and syncope. Serious hypoventilation may occur, and respiratory depression and laryngospasm may also result, particularly with IV administration. Hypersensitivity reactions, including

Prototype summary: Phenobarbitone Indications: Sedation, short-term treatment of insomnia, long-term treatment of tonic–clonic seizures and cortical focal seizures, emergency control of certain acute convulsive episodes, preanaesthetic. Actions: Inhibits conduction in the ascending RAS; depresses the cerebral cortex; alters cerebellar function; depresses motor output; can produce excitation, sedation, hypnosis, anaesthesia and deep coma; and has anticonvulsant activity. Pharmacokinetics: Route Peak Onset Duration Oral 15 mins 30–60 mins 10–16 hours IM 10–30 mins 4–6 hours IV up to 15 mins 5 mins 4–6 hours T 1/2 : 79 hours; metabolised in the liver, excreted in urine. Adverse effects: Somnolence, agitation, confusion, hyperkinesias, ataxia, vertigo, CNS depression, hallucinations, bradycardia, hypotension, syncope, nausea, vomiting, constipation, diarrhoea, hypoventilation, apnoea, withdrawal syndrome, rash. Clinically important drug–drug interactions Increased CNS depression results if these agents are taken with other CNS depressants, including alcohol, antihistamines and other tranquillisers. If other CNS depressants are used, dose adjustments are necessary. There is often an altered response to phenytoin if it is combined with barbiturates; evaluate the person frequently if this combination cannot be avoided. If bar- biturates are combined with monoamine oxidase (MAO) inhibitors, increased serum levels and effects occur. If the older sedatives/hypnotics are combined with MAO inhibitors, people should be monitored closely and nec- essary dose adjustments made. rash, serum sickness and Stevens–Johnson syndrome, which is sometimes fatal, may also occur.