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dopamine

dopamine

History:

  • The naturally occurring immediate precursor of noradrenaline;
  • was once used for cardiogenic shock with renal hypoperfusion;
  • was once used to counteract renal & mesenteric vasoconstriction with alpha-adrenergic doses adrenaline & noradrenaline;

Stability & preparation:

  • 40mg/ml 5ml; dilute by addition to saline &/or dextrose fluids;

Pharmacokinetics:

Routes of Administration:

  • Infusion as short T½
  • central line preferred
  • Monitor: blood volume; contractility; periph.perfusion;

Distribution:

  • Does not readily cross BBB → little effect on CNS receptors

Metabolism:

  • mainly by monoamine oxidase & COMT;

Excretion:

  • 97% in urine as metabolites; inhib. by probenecid; T½ 2min;

Pharmacodynamics:

<2µg/kg/min:

  • mainly acts on dopamine DA1 receptors:
    • ⇒ renal & mesenteric vasodilation
  • NB. “renal dose” dopamine does not effect clinical outcomes in pts with ARF (Ann Int Med April 2005)

2-5µg/kg/min:

  • dose-dep. beta (muscle vasodil.) & decr. NA release:
    • ⇒ unchanged total periph. resistance
    • ⇒ inc. CO; inc. SV; inc. contractility; inc.P initial only;
  • NB. HR depends on beta1→SAnode, DA2 →decr.NA rel.; vagal & symp.tone;

5-10µg/kg/min:

  • alpha effects as well (vasoconst.; inc. BP; inc. ven.press.;)

>20µg/kg/min:

  • mainly alpha → vasoconstriction mainly → resist.inc.;
    • ⇒ decr. renal & mesenteric blood flow & decr. urine output;
    • ⇒ risk of tachyarrythmias increases;

Bolus in arrest:

  • 2.5mg/kg approx = 45µg/kg adrenaline;

Side effects:

  • extravasation necrosis → large V; Rx with S/C local phentolamine;
  • ectopics; tachycardia; anginal pain; hypotension; vasoconstriction;
  • aberrant conduction; bradycardia; widened QRS; HT; gangrene;
  • N/V; headache; piloerection; SOB; azotaemia;

Toxic effects:

  • HT; marked decrease in pulse pressure;

Contraindications:

Major interactions:

  • incompatible with alkali & ? as for adrenaline / epinephrine;
  • MAOI ⇒ reduce starting dose to 1/10th;
  • alpha-beta blockers, etc. may cause complex interactions;
  • Probenecid ⇒ decr. excretion;
  • ? butyrophenones ⇒ block renal vasodilatation;
dopamine.txt · Last modified: 2012/01/17 15:04 (external edit)