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9780521704632c12 CUFX213A/Peck 9780521618168 December 28, 2007 12:15
Section IIICardiovascular drugsKinetics
Ephedrine is well absorbed orally, intramuscularly and subcutaneously. Unlike
adrenaline it is not metabolized by MAO or COMT and, therefore, has a longer dura-
tion of action and an elimination half-life of 4 hours. Some is metabolized in the liver
but 65% is excreted unchanged in the urine.Metaraminol
Metaraminol is a synthetic amine with both direct and indirect sympathomimetic
actions. It acts mainly viaα 1 -adrenoceptors but also retains someβ-adrenoceptor
activity.Presentation and uses
Metaraminol is presented as a clear solution containing 10 mg.ml−^1 .Itisused to
correct hypotension associated with spinal or epidural anaesthesia. An intravenous
bolus of 0.5–2 mg is usually sufficient.Effects
Cardiovascular – its main actions are to increase systemic vascular resistance,
which leads to an increased blood pressure. Despite its activity atβ-adrenoceptors
the cardiac output often drops in the face of the raised systemic vascular resistance.
Coronary artery flow increases by an indirect mechanism. Pulmonary vascular
resistance is also increased leading to raised pulmonary artery pressure.Other inotropic agents
Non-selective phosphodiesterase inhibitors
Aminophylline
Aminophylline is a methylxanthine derivative. It is a complex of 80% theophylline
and 20% ethylenediamine (which has no therapeutic effect but improves solubility).Presentation and uses
Aminophylline is available as tablets and as a solution for injection containing
25 mg.ml−^1 .Oralpreparations are often formulated as slow release due to its half-
life of about 6 hours. It is used in the treatment of asthma where the dose ranges
from 450 to 1250 mg daily. When given intravenously during acute severe asthma
aloading dose of 6 mg.kg−^1 over 20 minutes is given, followed by an infusion of
0.5 mg.kg−^1 .h−^1 .Itmay also be used to reduce the frequency of episodes of central
apnoea in premature neonates. It is very occasionally used in the treatment of heart
failure.