labetalol

see also beta blockers

• Racemic mixture of 4 isomers (beta-block 5 x alpha1-block):
  • RR: beta-block 4 x racemic; alpha1-block 20% of racemic; intrinsic beta2 agonist
  • RS: almost devoid blocker effects;
  • SR: almost no beta-block; alpha1-block 5 x racemic;
  • SS: almost no beta-block; alpha1-block approx racemic;
• ⇒ anti-HT,
• ⇒ arteriolar relaxation & vasodilation esp. in upright posture (alpha1-block);
• ⇒ vasodilation (beta 2 agonist);
• NB. also cocaine-like effect (decr. NA uptake);
• Labetalol is acceptable to use in breastfeeding

• Acute, severe hypertension during pregnancy or the post partum period

• Severe or uncontrolled asthma
• Uncontrolled congestive cardiac failure
• History of allergic disorders with a predisposition to bronchospasm
• Second or third degree AV block
• Sick sinus syndrome (without pacemaker)
• Shock (cardiogenic or hypovolaemic)
• Bradycardia with a heart rate <60bpm

Alternative antihypertensive agents including nifedipine (immediate release) or hydralazine should be used in patients with a contraindication to labetalol use.

• Available as an ampoule of clear fluid containing 100mg/20mL (i.e. 5mg/mL)
• Can be administered iv undiluted through an iv line primed with labetalol, and, preferably through a large bore iv cannula
• Can be administered in same iv line but through a different port, with magnesium sulphate in patients with pre-eclampsia and eclampsia
• adults via syringe driver:
  • 100mg in 20mL (5mg/mL) drawn up undiluted into a 20mL syringe
  • 1st bolus: 20mg over 2 minutes then flush with 10mL 0.9% saline
  • optional 2nd and 3rd boluses if inadequate response within 10 minutes: 20-40mg over 2 minutes then flush with 10mL 0.9% saline (3rd bolus can be increased to 60mg if needed)
  • Maintenance infusion:
    • Commence at 20mg/hr and titrate according to response
    • Discontinue by weaning over 1-2 hours when blood pressure is consistently less than 155 / 95 mm Hg
    • If the systolic blood pressure <140mmHg or diastolic <90mmHg cease infusion and consider bolus iv fluid

• iv bolus:
  • 10mg (2mL) given as slow IV injection over 1-2 minutes (given UNDILUTED)
  • Dose can be repeated at 10 minute intervals, titrate to desired systolic/diastolic BP
• iv infusion
  • 200mg (2 vials = 40mL) into 250mL fluid (withdraw 40ml)
  • Infuse at 3mL/minute to give approximately 2.5mg/min
  • Maximum dose 300mg in 24 hours