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What is the MOA of amiodarone?
Class III antiarrhythmic: blocks K+ channels which prolongs the repolarization and refractory period in the atrial and ventricular tissue
Also has same MOA as all other drugs (Na+, BB, CCB)
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What are some common uses for amiodarone?
- Supraventricular and ventricular tachycardia (VT, VF, A fib or flutter)
- Cardiac arrerst
- Prevention of post-operative AF during cardiothoracid surgery
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Where does amiodarone typically concentrate?
Fat tissues
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What type of absorption does amiodarone have?
Slow and incomplete
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Does food enhance or decrease the rate and extent of absorption? (AUC and Cmax)
Enhance: Increase AUC and Cmax
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What is the bioavailability of oral amiodarone?
50%
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What type of circulation does amiodarone undergo?
Enterohepatic circulation
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What percentage of amiodarone is protein bound?
96%
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What two proteins does amiodarone bind with?
- albumin
- alpha-1-acid glycoprotein
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What is the approximate volume of distribution of amiodarone?
60 L/kg
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What are the major sites of distribution for amiodarone?
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_________ cocentration 10-400 times greater than ________ concentrations
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Does amiodarone follow a one or two compartment model?
two
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What is the active metabolite of amiodarone?
Desethylamiodarone (DEA)
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Is the process of amiodarone being distributed to the tissues slow or fast?
Slow
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What is a major enzyme that metabolizes amiodarone?
3A4
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What enzyme(s) and/or transporter (s) is/are inhibited by amiodarone?
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Does amiodarone need to be adjusted in renal dysfunction?
No
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What is the 1/2 life for chronic oral dosing of amiodarone?
53 days
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What is the 1/2 life for IV amiodarone?
9 to 36 days
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Is the half life of N-DEA greater, less than, or equal to amiodarone?
Greater than or equal
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What are two factors that alter the clearance of amiodarone?
- Cirrhosis: decreases formation of DEA
- Elderly: decreased clearance
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What effect does renal failure, heart failure, or dialysis have on amiodarone?
None
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What is the onset of action of amiodarone?
1-3 weeks
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What is the duration of amiodarone?
30-90 days
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What is the therapeutic range of amiodarone?
0.5-2.0 mg/L
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When is the peak concentration of amiodarone?
3-7 hours
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What is the oral LD for amiodarone?
1.2-1.8 g/day in divided doses up to 10 grams
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What is the IV LD for amiodarone?
5-7 mg/kg over 30-60 minutes, then 1.2-1.8 g/day continuous infusion up to 10 grams
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What is the maintenance dose for amiodarone?
200-400 mg/day
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If the patient has been on IV therapy for < 1 week, what is the oral LD that should be given?
800-1600 mg/day for 1-2 weeks followed by a MD
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If the patient has been on IV therapy for 1 to < 3 weeks, what is the oral LD that should be given?
600-800 mg/day for 1-2 weeks followed by a MD
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If the patient has been on IV therapy for > 3 weeks, what is the oral LD that should be given?
None, go ahead and start with the MD
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When switching from oral to IV amiodarone, how should the dose be adjusted?
Give 50% of oral dose when switching to IV
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Which drugs can caused a prolonged QT interval when used with amiodarone?
- Azole antifungals
- Macrolides (erythromycin, clarithromycin)
- Fluoroquinolones
- Haloperidol
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Which drugs can cause delayed AV node conduction when used with amiodarone?
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When using digoxin and amiodarone together, what adjustment should be made?
Decrease the digoxin dose by 50%
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When using warfarin and amiodarone together, what adjustments hould be made?
Decrease the warfarin dose by 25%
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What drugs may have increased concentrations when administered with amiodarone?
- Digoxin
- Sildenafil
- Cyclosporine
- Tacrolimus
- Theophylline
- Warfarin
- Atorvastatin
- Simvastatin
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What drugs will decrease amiodarone levels?
- Phenytoin
- Phenobarbital
- Rifampin
- St. Johns Wort
- Cholestyramine
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What drugs will increase amiodarone levels?
- Grapefruit Juice
- Protease inhibitors
- Cimetidine
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Approximately how much of an increase in amiodarone levels would you expect to see when administered with grapefruit juice?
50%
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If amiodarone is given too quickly through an IV what are some AE that can happen?
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In order to prevent phlebitis, what is the cut off for giving central line amiodarone?
> 2 mg/nL
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What are some toxicites that can occur due to the MOA of amiodarone?
- Sinus bradycardia
- Atrioventricular block
- QT prolongation (rarely torsades)
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What are some proposed etiologies of toxicity related to chronic therapy?
- Long 1/2 life : accumulation of amiodarone and iodine
- Lipophilic distribution into adipose tissues of multiple organs
- Phospholipidosis : abnormal lipid storage
- Free radical formation
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At what dose do most toxicites occur?
> 400 mg/day
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What types of pulmonary toxicites are possible with amiodarone?
- Pulmonary fibrosis
- Hypersensitivity Pneumonitis
- Pulmonary inflammation
- Interstitial or alveolar Pneumonitis
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What is the MOA of pulmonary toxicity with amiodarone?
Abnormal phospholipid storage in lysosomal cells leading to membrane stiffness and cell damage
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Is pulmonary toxicity independent or depending on dose and/or duration of therapy?
Dependent
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Does pre-existing pulmonary disease increase the risk of pulmonary toxicity?
No, but it may worsen the prognosis
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What are some signs and symptoms of pulmonary toxicity?
- Nonproductive cough
- Dyspnea
- Pleuritic chest pain
- Weight loss
- Malaise
- Asymptomatic
- CSR: interstitial or alveolar infiltrates and/or extensive pulmonary fibrosis
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What types of hepatic toxicity are seen with amiodarone?
- Transient elevation in LFTs
- Clinical hepatitis and cirrhosis
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What are the signs and symptoms of hepatic toxicity?
- Asymptomatic
- Typical signs of liver failure (side pain, jaundice)
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What is the MOA of hepatic toxicity?
- Phospholipidosis
- Direct toxic effects
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Is it more common to see HYPOthyroidism or HYPERthyroidism with amiodarone?
HYPOthyroidism
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What is the MOA of thyroid toxicity with amiodarone?
- Excess iodine intake
- Amiodarone blocks conversion of T4 to T3 --> inactive thyroid hormonres
- Also leads to decreased synthesis of T4
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Is thyroid toxicity dependent or independent of dose/duration?
Independent
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What are two ocular toxicities that occur due to amiodarone?
- Corneal microdeposits
- Opetic neuropathy
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What are symptoms of corneal microdeposits?
- Asymptomatic
- Present with corneal cysts or abscesses
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What is the MOA of corneal microdeposits?
Secretion of amiodarone by the lacrimal glands and deposits on the surface of the cornea
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What are two dermatologic toxicites of amiodarone?
- Photosensitivity
- Blue-gray skin discoloration
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What is the MOA of blue-gray skin?
Photosensitive reaction resulting in lipofuscion deposits instead of melanin and pigment
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In what patient population are neurologic toxicities more common? Is it independent or dependent of dose?
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Are corneal microdeposits related or non-related to drug dose/duration?
Related
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What should you monitor at baseline for amiodarone use?
- EKG
- LFTs
- PFTs
- CXR
- TFTs
- Eye exam
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What tests should be ordered at 6 months post amiodarone?
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What tests should be ordered annually?
- PFTs (symptoms only)
- CXR (symptoms)
- EKG
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