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Seth Adams Duy Cao Scott Davis Cheryl Hanslovan Bryan Ing Kristin McKay Vic Patel Dan Rackham Darren Smith Phong Vuong. Digoxin (Lanoxin/Lanoxicaps). foxglove digitalis. General Structure. Mechanism of Action.

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Digoxin lanoxin lanoxicaps

Seth Adams

Duy Cao

Scott Davis

Cheryl Hanslovan

Bryan Ing

Kristin McKay

Vic Patel

Dan Rackham

Darren Smith

Phong Vuong

Digoxin (Lanoxin/Lanoxicaps)

foxglove digitalis



Mechanism of action
Mechanism of Action

  • Digoxin inhibits membrane bound sodium-potassium ATPase resulting in an increased intracellular [Na+] and thus an increase in the intracellular [Ca2+] by stimulation of Na+ and Ca2+ exchange.

  • Digoxin has an indirect effect on the sinoatrial and atrioventricular nodes (vagomimetic actions).

  • Baroreceptor sensitization also results from digoxin. This leads to increased afferent inhibitory activity and reduced activity of the sympathetic nervous system and renin-angiotensin system.


Digoxin lanoxin lanoxicaps

Digoxin

(-)

2

+

Ca

+

3Na

+

2K

NaCaX

ATPase

+

3Na

Ca2+

RyR

ATP

Ca2+

2

+

ATPase

Ca

SR

ADP

Contraction


Net effect
Net Effect

  • Positive inotropic action (an increase in the force and velocity of myocardial systolic contraction).

  • A decrease in the degree of activation of the sympathetic nervous system and renin-angiotensin system.

  • Slowing of the heart rate and decreased conduction velocity through the AV node.


Main clinical indications
Main Clinical Indications

  • Heart Failure

    • Increases cardiac output by positive inotropic actions

    • Therapeutic level of 0.5-1 mcg/L

  • Atrial Fibrillation

    • Rate control by vagomimetic actions

    • Therapeutic level of 0.5-2 mcg/L


Available dosage forms
Available Dosage Forms

  • Tablets ( F = 0.6 - 0.7)

    • 125 mcg ( yellow, # Y3B ) or 250 mcg ( white, # X3A )

  • Capsules (Lanoxicaps) ( F = 0.9 – 0.95)

    • 50 mcg ( red, # A2C ) , 100 mcg ( yellow, # B2C ), and 200 mcg ( green, # C2C)

  • Pediatric Elixer ( F = 0.75 – 0.85)

    • 50 mcg per 1 ml (10% alcohol)

  • Injection ( F = 1.0 )

    • 250 mcg per 1 ml (1 ml ampule)

  • Pediatric Injection ( F = 1.0 )

    • 100 mcg per 1 ml (1 ml ampule)


Side effects toxicities
Side Effects & Toxicities

  • Yellow/green visual changes, halos around light

  • N&V and diarrhea (50-75% of patients)

  • Bradycardia (75-90% of patients)

  • Fatigue, malaise, confusion, headache, etc.

  • Anorexia


Drug interactions
Drug Interactions

  • Amiodarone

    • ↑[Digoxin] by 70%

  • Verapamil

    • ↑[Digoxin] by 50-75%

  • Propafenone

    • ↑[Digoxin] by 30%

  • Quinidine

    • ↑[Digoxin] by 50-75%

  • Erythromycin

    • ↑[Digoxin]


Pharmacokinetic parameters
PharmacokineticParameters

  • Absorption

    • After oral dosing:

      • Onset of action in 0.5 – 2 hours

      • Peak effect reached in 2 – 6 hours

  • Distribution

    • Skeletal and heart muscle, but not into adipose tissue

    • Up to 25-30% is bound to plasma proteins

  • Metabolism

    • Follows first-order kinetics

    • Limited metabolism via sugar hydrolysis and lactone ring reduction

    • Half-life = 1-2 days

  • Excretion

    • 60-80% excreted unchanged in urine

    • Undergoes ACTIVE tubular secretion in the kidneys


Clinical considerations
Clinical Considerations

  • Doses must be individualized and depends on the type & severity of the disease, age & weight of the patient, renal function, and concomitant disease states

  • Normal dosage range is 125 – 500 mcg (50 – 200 mcg capsules) a day in a single dose

  • Contraindications: Patients w/ ventricular fibrillation, renal impairment, hypokalemia, hypomagnesemia, hypercalcemia, and pulmonary disease

  • Patient must be advised not to take nonprescription cough or cold medications, antacids, laxatives, or antidiarrheals without consulting the pharmacist or physician

  • Pregnancy category C


Digoxin equations
Digoxin Equations

  • IBW = 50 (or 45.5) + 2.3 x (inches over 60)

  • CrCl = ((140 - Age) x IBW) / (72 x SCr) ( x 0.85 for females)

  • Clearance Digoxin: Cldig = (0.8 ml/min/kg x IBW) + CrCl

    • w/ CHF: Cl = (0.33 ml/min/kg x IBW) + (0.9 x CrCl) (these values were multiplied by 0.06 to convert them from mL/min to L/hr)

    • w/ co-administration of amiodarone: Cl = 0.5 x Cl (without amiodarone)

  • Vd = 7.3 L/kg x IBW

    • w/ renal dysfunction: Vd = (3.8 L/kg x IBW) + (3.1 x CrCl)

  • LD = (Cp (desired level) x Vd) / (F)

  • MD = (Cp (desired level) x Cldig x Xo) / (F)


Sample problems
Sample Problems

  • WB is a 75-year-old female with PMH including atrial fibrillation, type II diabetes, hypertension, and renal insufficiency. She is 5’4” and weighs 75 kg. Her SCr is 3.4 mg/dL. Calculate a loading and maintenance dose for Lanoxin tablets for Mrs. B.

    • Target Cpss = 1.0 mcg/L for atrial fibrillation

  • AS is a 78-year-old male with CHF. He is 5’10” and weighs 73kg. His SCr is 1.1 mg/dL. Calculate a dosing regimen using Lanoxicaps.

    • Target Cpss = 0.7 mcg/L for CHF


Problem solutions 1
Problem Solutions - 1

  • WB w/ Renal Dysfunction:

    • IBW = 45.5 kg + 2.3 (4 in) = 54.7 kg

    • CrCl = ((140-75) x 54.7 kg (.85)) / (3.4 x 72) = 12.35 mL/min

    • Vd = (3.8 L/kg x 54.7 kg) + 3.1 (12.35 mL/min) = 246.15 L

    • Cldig= (0.8 mL/min/kg x 54.7 kg) + 12.35 mL/min = 56.11 mL/min = 3.37 L/hr

    • LD = (246.15 L x 1 mcg) / (0.7) = 351.64 mcg  Use 375 mcg tabs once

    • MD = Cpss = 1 mcg/L = (Xo(0.7)) / (3.37 L/hr x 24 hr)  0.7Xo = 80.88 mcg  Xo = 115.54 mcg  Use 125 mcg tabs qday


Problem solutions 2
Problem Solutions - 2

  • AS w/ Congestive Heart Failure:

    • IBW = 50.0 kg + 2.3 (10 in) = 73 kg

    • CrCl = ((140-78) x 73 kg) / (1.1 x 72) = 57.15 mL/min

    • Vd = (7.3 L/kg x 73 kg) = 532.9 L

    • Cldig= (0.33 mL/min/kg x 73 kg) + 0.9 (57.15 mL/min) = 75.52 mL/min = 4.53 L/hr

    • LD = (532.9 L x 0.7 mcg) / (0.95) = 392.66 mcg  Use 400 mcg caps once

    • MD = Cpss = 0.7 mcg/L = (Xo(0.95)) / (4.53 L/hr x 24 hr)  0.95Xo = 76.1 mcg  Xo = 80.11 mcg  Use 100 mcg caps qday


References
References

  • 20th edition top 200 pharmacy drug cards. SFI Medical Publishing. 2004.

  • Class lecture. Pharmacy 750. 11/3/2005. Connie Covington

  • Tharp, R. (2006) Digoxin Dosing. Retrieved March 9, 2006 from the world wide web: http://www.rxkinetics.com/dig.html

  • Medicinal Plants. (2006) Digoxin Image. Updated Aug 12, 2005. Retrieved March 8, 2006 from world wide web: http://www.science.siu.edu/plant-biology/PLB117/Nickrent.Lecs/Medicine.html

  • Rx-List. (2006) Digoxin. Updated March 12, 2006. Retrieved March 8, 2006 from world wide web: http://www.rxlist.com/cgi/rxlist.cgi?drug=digoxin

  • Digoxin Structure. Retrieved March 8, 2006 from world wide web: http://medpharm.chunma.ac.kr/Aldja/CVS/cardiac_glycoside/img/digoxin_structure.GIF