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Section IIICardiovascular drugsPreparation and uses
Milrinone is formulated as a yellow solution containing 1 mg.ml−^1 and may be stored
at room temperature. It should be diluted before administration and should only be
used intravenously for the short-term management of cardiac failure.Kinetics
Approximately 70% is plasma protein bound. It has an elimination half-life of 1–2.5
hours and is 80% excreted in the urine unchanged. The dose should be reduced in
renal failure.Amrinone
Amrinone is not available in the UK. It has a similar pharmacological profile to
the other selective phosphodiesterase inhibitors. Approximately 40% is excreted
unchanged in the urine. One in 40 patients suffers a reversible dose-related throm-
bocytopenia.Glucagon
Within the pancreas,α-cells secrete the polypeptide glucagon. The activation of
glucagon receptors, via G-protein mediated mechanisms, stimulates adenylate
cyclase and increases intracellular cAMP. It has only a limited role in cardiac failure,
occasionally being used in the treatment ofβ-blocker overdose by an initial bolus of
10 mg followed by infusion of up to 5 mg.hr−^1 .Hyperglycaemia and hyperkalaemia
may complicate its use.Ca^2 +
While intravenously administered Ca^2 +salts often improve blood pressure for a few
minutes, their use should be restricted to circulatory collapse due to hyperkalaemia
and Ca^2 +channel antagonist overdose.T 3
Thyroxine (T 4 ) and triiodothyronine (T 3 ) have positive inotropic and chronotropic
effects via intracellular mechanisms. They are only used to treat hypothyroidism and
are discussed in more detail in Chapter 25.