CLASS III ANTIARRHYTHMIC DRUG-

Chemical structure:

☛ Benzofuran derivative
☛ First line anti arrythmc derivative in cardio pulmonary resuscitation by ATSA in VT
☛ Effective prophylactically in preventing AF post operatively.
☛ Wide spectrum of effectiveness including supraventricular and preexcitation syndrome.

 

Actions:

1. Increase APD
2. Decrease the slope of diastolic depolarization(phase 4) with depressed SA Node automaticity
3. Amiodarone prolomgs repolarisation and refracteriness in the SA Node in atria and ventricular myocardium in AV Node and HIS-PURKINJE system
4. Resting potential and myocardial automaticity are minimally affected but both ERP and Refractory [period are prolonged].
5. Blocks inactive sodium channels in purkinje fibers with significantly depress phase 0
6. They decrease AV junctional and SA Nodal automaticity and prolongs intranodal conduction.

 

Electrophysiologic effects of chronic amiodarone mimic those of thyroid ablation.

Blockage of cardiac effect of T3 . This mechanism has been propsed as an alternative to the active metabolic accumulation to account for the slow onset of anti arrythmic effect of Amiodarone.

Amiodarone increase the amount of electric cuirrent required to elicit VF.

Increase VF threshold –Selective increased activity in diseased tissue.

 

Haemodynamic Effect:

1. Decrease heart rate , mean aortic pressure, Heart rate and peak left ventricularpr .
2. Cardiac outpit was increased despite the negative ionotropic effect as a result o9f decrease in left ventricular afterload.
3. Haemodynamic detoriation may occur in same patients with compensated CHF because of anti adrenergic effects of the drug.

 PH k:

☛ Low bioavailability, very large half life, relatively low clearance and large volume of distribution
☛ Oral absorption is slow with peak plasma levels 3-7 hours after ingestion
☛ Plasma half life:14-107 days

 

Infusin doses:

0.5 to 3.9 mg/min and maintainence dose of 0.5to 1mg/min . This dose reduces VT by 85%, paired PVCs by 74%

☛ Oral loading dose
☛ 800mg/day for 7days
☛ 600mg/day for 3days
☛ IV 5mg/kg for 30 minutes
☛ 150 mg IV bolus followed by 1 mg/min for 6hours and 0.5 mg/min thereafter.
☛ In CPR 3oomg IV bolus is given and repeated with multiple boluses if defibrillation is unsuccessful

 

ADVERSE EFFECTS:

1. Photosensitivity : Abnormal pigmentation erythematous , pruritic rash , corneal micro depositions.
2. Pulmonary:Excertional dyspnea , cough, and weight loss , hypoxia may occur . CXR-Diffuse bilateral interstitial infiltrates because of abnormal production of phospholipids
3. Thyroid abnormalities : Hyper/Hypo Amiodarone contains two iodine atoms , 75mg of organic iodide , 200 mg of drug,10% becomes free iodine , heart rate does not increase because of anti adrenergic effect.
4.                                                                                                                        dr.ajita