Clonidine

Clonidine - is an a2-adrenoceptor agonist which may have a protective effect on cardiovascular morbidity and mortality in the critically ill patient.The mechanism of the protective effect is likely to be manifold. a2-adrenoceptor agonists attenuate haemodynamic instability, inhibit central sympathetic discharge, reduce peripheral norepinephrine release and dilate post-stenotic coronary vessels. Its use as an antihypertensive agent has since been superseded by other drugs. It has a useful sedative property, which is synergistic with opioids and other sedative agents. It is a useful short-term adjuvant to sedation especially following extubation where there is a high sympathetic drive and in the agitated patient. Its usage should not usually exceed 3 days, as withdrawal can lead to rebound hypertension and agitation.

Uses:
Short-term adjunct to sedation (unlicensed)

Contraindications:
Hypotension
Porphyria

Administration:
• IV bolus: 50 μg 8 hourly, given slowly over 10–15 min, may be increased gradually to 250 μg 8 hourly
• IV infusion: 30–100 μg/h
Compatible with glucose 5% and sodium chloride 0.9%
Oral: 50 μg 8 hourly, may be increased gradually to 400 μg 8 hourly

How not to use clonidine:
Sudden withdrawal if used for longer than 3 days

Adverse effects:
Bradycardia
Hypotension
Fluid retention
Dry mouth
Sedation
Depression
Constipation

Cautions
Avoid prolonged use and sudden withdrawal (rebound hypertension)
Peripheral vascular disease (concomitant use with beta blockers may worsen condition)
Second-degree heart block (may progress to complete heart block)

Avoid concomitant use with:
Beta-blockers (bradycardia)
Tricyclics (counteract effect)
NSAIDs (sodium and water retention)
Digoxin (bradycardia)
Haloperidol (prolongation of QT interval)

Organ failure:
Renal: no dose reduction necessary in renal failure, though plasma levels are higher in severe renal dysfunction