Assessment of drugs in schizophrenia. Assessment of psychiatric and social state. 20V

Labetalol (Trandate, Glaxo Inc.; Normodyne, Schering Corp.)

Labetalol is a competitive antagonist of α1-, β1-, and β2-adrenergic receptors. The hemodynamic effects of the drug include reduced blood pressure, heart rate, and peripheral resistance, with little change in resting cardiac output or stroke volume. In open trials and controlled studies, labetalol was an effective antihypertensive. Labetalol compared favorably with β-blockers alone or in combination with vasodilators, for the treatment of hypertension. Reductions in heart rate are less pronounced with labetalol as compared with propranolol. Labetalol produces rapid reductions in blood pressure when administered intravenously for severe hypertension. The most frequent adverse reactions to the drug include fatigue, postural symptoms, headache, and gastrointestinal complaints. Labetalol may prove advantageous when vasodilation in addition to β-blockade is desired, or for selected patients experiencing adverse effects attributable to β-blockade. Until the clinical profile of labetalol is better defined, the use of the drug should be limited.

[Perioperative beta-blockers. Part two: therapeutic indications]

PURPOSE

To review the pharmacologic and pathophysiologic information necessary to prescribe beta-blockers (BB) in perioperative medicine.

DATA SOURCE

Manual retrieval and electronic research of the literature using MEDLINE (key-words: anesthesia and beta- blocker; surgery and beta-blocker).

DATA SYNTHESIS

In non cardiac surgery, the beneficial effects of BB have been demonstrated in hypertensive patients since 1979. In 1996, the beneficial effects of atenolol in patients with coronary artery disease (reduction of postoperative myocardial ischemia and overall reduction in two-year mortality) were demonstrated. In coronary surgery, the interest of preoperative BB treatment has been shown since 1983. Administration of BB has been shown to be beneficial in acute myocardial infarction or chronic cardiac failure (except in NYHA class IV patients).

CONCLUSION

BB have been shown to exert a beneficial effect on postoperative outcomes in patients with cardiovascular disease or risk factors, and their more widespread use in perioperative medicine is encouraged.

The influence of labetalol on arterial blood gas data, pulmonary haemodynamics and pulmonary shunting

The arterial oxygen and carbon dioxide tensions, pulmonary and systemic haemodynamics and pulmonary shunting and mechanics were measured during the first 30 min after intravenous labetalol administration. Thirty patients, recovering in the intensive care unit after neurosurgical interventions were randomly divided in 2 groups of 15 patients, receiving either labetalol or placebo. In the labetalol treated group the arterial oxygen tension decreased from 553.6 +/- 16.8 to 529.3 +/- 19.8 mmHg 5 min after the injection of labetalol. A concomitant increase in arterial carbon dioxide tension from 40.1 +/- 1.1 to 45.5 +/- 1.3 mmHg was noticed. Pulmonary vascular resistance decreased from 159.6 +/- 14.7 to 116.7 +/- 11.7 dynes.sec.cm-5 and pulmonary shunting increased from 4.8% +/- 1.4% to 8.1% +/- 2.4% 5 min following injection. All these changes were statistically significant for p less than 0.01. After 30 min all values had returned to their initial level. No changes were registered in the control group. As airway resistance appeared not to be affected by the labetalol administration it may be concluded that the observed changes in blood gas data are most likely due to a transient decrease of the pulmonary vascular resistance with a concomitant increase in pulmonary shunting.

Synergism between halothane and labetalol

A patient in chronic renal failure, who was receiving large doses of the combined alpha- and beta-blocking agent, labetalol, was selected for renal transplantation. A low concentration of halothane was used for induction and maintenance of anaesthesia, but severe myocardial depression occurred which proved unresponsive to atropine or isoprenaline, although it responded to a dopamine infusion. Synergism has already been reported between labetalol and high concentrations of halothane, but this case suggests that, in patients with previous myocardial damage, much lower concentrations of this inhalational agent may prove fatal.

N-acetyl-p-amino-phenol (paracetamol, acetaminophen) in the treatment of acute schizophrenia

The hypothesis that schizophrenia is caused by the release of prostaglandin E into the hypothalamus and may sometimes be accompanied by an elevation of temperature was examined by a clinical trial of the prostaglandin E suppressant N-acetyl-p-amino-phenol (paracetamol, acetaminophen). Ten acute schizophrenic patients were included in a double-blind, crossover trial of paracetamol and a placebo, in which each treatment was given for a week. Regular 4-hourly temperatures were recorded in all these cases and in 5 non-schizophrenic patients for comparison. The findings provided no evidence that paracetamol mitigated the symptoms of schizophrenia. The temperatures of the schizophrenics were not elevated more than those of the controls, but the number of cases used was probably too small for this finding to be conclusive.

Circulatory effects of labetalol during halothane anaesthesia

Labetalol is a drug possessing both alpha and beta adrenergic receptor blocking properties. Its possible use in induced hypotension during halothane anaesthesia has been investigated. It causes a satisfactory decrease in arterial pressure unaccompanied by tachycardia. The circulatory effects of the drug during halothane anaesthesia, both with spontaneous and controlled respiration, have been measured and compared with those of halothane alone. In patients anaesthetised with 1% halothane, labetalol, with both spontaneous and controlled ventilation, was associated with a reduction in MAP from 71.5 mmHg to 54.0 mmHg (P less than 0.001) and 66.8 mmHg to 50.4 mmHg (P less than 0.001) respectively. This reduction was associated with decreases in Qt of 18% and 12% respectively. In the presence of labetalol, with 3% halothane and spontaneous respiration, the depressant effects of the anaesthetic on the heart became rapidly apparent: Qt was reduced by a further 28%. In patients not receiving labetalol, the depressant effects of 3% halothane were frequently countered by the positive inotropic effects of hypercarbia.

Poor hypotensive response and tachyphylaxis following intravenous labetalol

Three renal patients with transplant kidneys and uncontrolled hypertension were treated with intravenous doses of labetalol. Only minor depressor effects were noted and tachyphylaxis developed in 1 patient. Other parenteral hypotensive agents reduced blood pressure satisfactorily.