Inamrinone
Inamrinone (formerly known as amrinone) is a **bipyridine positive inotropic agent** and vasodilator (often referred to as an inodilator). - **Second-line agent** for the short-term management of congestive heart failure (CHF). - Structurally unrelated to cardiac glycosides or catecholamines. - Very expensive and requires intensive monitoring in a hospital setting. > **Clinical Pearl:** The drug's name was officially changed from amrinone to inamrinone to prevent potentially fatal medication errors caused by confusion with the antiarrhythmic drug *amiodarone*.
Mechanism: Inamrinone acts primarily as a **phosphodiesterase III (PDE3) inhibitor**. - **Inhibition of PDE3** → decreased breakdown of intracellular cyclic AMP (cAMP) → increased intracellular calcium in the myocardium → **positive inotropy** (direct stimulation of cardiac contractility). - In vascular smooth muscle, increased cAMP leads to relaxation → **vasodilation**, which effectively reduces both cardiac preload and afterload.
Dosing by species
- Positive inotropic agent · 1-3 mg/kg IV followed by 30-100 micro-grams/kg/min IV infusion · IV · CRI
- Positive inotropic agent · 1-3 mg/kg IV as a slow IV bolus followed by a 10-100 micrograms/kg/min IV CRI; ½ the initial bolus may be administered 20-30 minutes after the first bolus. · IV · CRI
- Positive inotropic agent · 1-3 mg/kg IV as a slow IV bolus followed by a 10-100 micrograms/kg/min IV CRI; ½ the initial bolus may be administered 20-30 minutes after the first bolus. · IV · CRI
- Positive inotropic agent · 1-3 mg/kg IV followed by a 30-100 micrograms/kg/min IV CRI · IV · CRI
- Positive inotropic agent · 2 mg/kg bolus IV , followed by 30-300 micrograms/kg/min IV infusion · IV · CRI
- For patients coming off cardiopulmonary bypass with poor cardiac contractility · 0.25-0.6 mg/kg loading, then 5-45 micrograms/kg/min CRI · IV · CRI
- Adjunctive treatment for calcium channel blocker overdose · 30-100 micrograms/kg/min CRI. · IV · CRI · Alternative to dopamine or dobutamine; used with fluids, IV calcium, and potentially glucagon.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Routes of administration
Contraindications
- Severe aortic or pulmonic valve disease
- Hypersensitivity to inamrinone or bisulfites
Adverse effects
- Arrhythmias
- Hypotension
- Vomiting
- Diarrhea
- Thrombocytopenia (particularly with prolonged therapy)
- Hepatotoxicity
- Hypersensitivity reactions (variable symptomatology: pericarditis to myositis)
Drug interactions
- Digoxin · Additive inotropic effect; generally considered a positive drug interaction.
- Disopyramide · May cause excessive hypotension when used concurrently.
Monitoring
- Blood pressure
- Heart rate/rhythm (continuous ECG recommended)
- Body weight
- Platelet counts
Overdose
Because **hypotension** is the primary problem that would generally be seen, circulatory support should be instituted immediately. Only one human case of accidental massive overdose resulting in death has been reported (causal relationship not unequivocally established).
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.