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Clinical pharmacokinetics: Digoxin
YOUAN BI BENIET MARIUS
Pharm D, Master student in clinical Pharmacy
University of Nairo...
Outlines
INTRODUCTION
Part I : Pharmacokinetics of Digoxin
Part II : Determination of Digoxin dose regimen
CONCLUSION
Introduction
 Digoxin: primary cardiac glycoside in clinical use
 Main Clinical Indications:
 Atrial Fibrillation
Thera...
Introduction
 Pediatric Injection
– 100 mcg per 1 ml (1 ml ampule)
 Tablets
62.5 ; 125 mcg ( yellow,) or 250 mcg ( white,)
 Capsules...
Introduction
 narrow therapeutic index
 Most prominent features of the clinical use of digoxin
 An endpoint of therapy ...
Introduction
 This condition has Led to the development of
monograms and equations designed to estimate
optimal digoxin d...
 understanding the clinical pharmacokinetics of
Digoxin will help us to improve in the dosage
regimens design and ‘‘thera...
Objective
 To Describe the profile of digoxin concentration in
the body which depend of his absorption,
distribution, met...
I-Pharmacokinetics of Digoxin
Absorption
 80 % absorbed after oral administration of tablets
 75-80 % absorbed after adm...
I-Pharmacokinetics of Digoxin
Absorption: factors affecting bioavailability
 40 % degraded by intestinal bacteria 1 in 10...
1. serum digoxin concentration–time curve follows a
two-compartment model
2. 8-12 hours tissues distribution phase.
DIGOXI...
DIGOXIN LEVELS after IV
Dose
Distribution
3. During the distribution phase, digoxin in the serum
is not in equilibrium wit...
Distribution
 Bound tightly to muscles tissues Vd Correlated well
with lean body Tissues , very large distribution volume...
 Less than 10 % undergoes hepatic metabolism
 not dependent of the cytochrome P450 system
and it is not know to induce o...
 Digoxin Elimination follows first-order kinetics
 50-70% is excreted almost entirely unchanged by
the kidney
 Affected...
Determination of Digoxin dose
regimen
Factors Units
Minimum effective concentration, 0.5 ng/mL
Maximum safe concentration
...
Digoxin Equation
w/ renal dysfunction: Vd = (3.12 x CLcr* + 3.84) CT* x IBW
 IBW = 50 (or 45.5) + 2.3 x (inches over 60)
...
Digoxin Case
WB is a 75-year-old female with PMH including atrial
fibrillation, type II diabetes, hypertension, and renal
...
CALCULATE LOADING DOSE (1/3)
LD = Vd x Cp/F
where Vd = Volume of distribution (liters)
Cp = target serum level (mcg/l)
F =...
 WB w/ Renal Dysfunction
Vd = (3.12 x CLcr + 3.84) CT x IBW
 CLcr = ((140 - Age) x IBW) / (72 x SCr) ( x 0.85 for female...
 WB w/ Atrial fibrillation
Target Cpss = 1.0 mcg/L
Lanoxin tablets Dose regimen for
F = bioavailability factor = 0.75
LD...
CALCULATE MAINTENANCE DOSE
(1/3)
MD = (Cldig x Cp x tau) / F
where Cldig = Digoxin clearance (l/hr)
Cp = target serum leve...
CALCULATE OF MAINTENANCE DOSE
(2/3)
Cldig = Digoxin clearance
((140-75) x 54.7 kg (.85)) / (3.4 x 72) = 12.35 mL/min CLcr...
Cldig 3.37 L/hr
Target Cpss = 1.0 mcg/L
tau = 24hours
F tablets = 0.7
=
MD = (3.37 L/h x 1 mcg/L x 24h ) / 0.7 =115.54 mcg...
Conclusion
 Digoxin is a very cheap and effective drug and
therefore useful clinically in heart failure
 equations desig...
References
 20th
edition top 200 pharmacy drug cards. SFI Medical Publishing. 2004.
 Tharp, R. (2006) Digoxin Dosing. : ...
Thank you very much
For your attention!!!
Clinical pharmacokinetics of digoxin
Clinical pharmacokinetics of digoxin
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Digoxin : Clinical pharmacokinetics
Pharmacokinetics (ADME) and Digoxin case study

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Clinical pharmacokinetics of digoxin

  1. 1. Clinical pharmacokinetics: Digoxin YOUAN BI BENIET MARIUS Pharm D, Master student in clinical Pharmacy University of Nairobi
  2. 2. Outlines INTRODUCTION Part I : Pharmacokinetics of Digoxin Part II : Determination of Digoxin dose regimen CONCLUSION
  3. 3. Introduction  Digoxin: primary cardiac glycoside in clinical use  Main Clinical Indications:  Atrial Fibrillation Therapeutic level of 0.5-1 mcg/L  Heart Failure Increases cardiac output by (+) inotropic actions Rate control by (-) chronotropic effects Therapeutic level of 0.5-2 mcg/L  Digoxin :naturally occurring drug (Digitalis spp.)
  4. 4. Introduction
  5. 5.  Pediatric Injection – 100 mcg per 1 ml (1 ml ampule)  Tablets 62.5 ; 125 mcg ( yellow,) or 250 mcg ( white,)  Capsules (Lanoxicaps) – 50 mcg ( red,) , 100 mcg ( yellow,), and 200 mcg ( green,  Pediatric Elixir – 50 mcg per 1 ml (10% alcohol)  Injection 250 mcg per 1 ml (1 ml ampule) Introduction
  6. 6. Introduction  narrow therapeutic index  Most prominent features of the clinical use of digoxin  An endpoint of therapy which is difficult to define and measure due to great variability in serum digoxin concentrations in patients given the same dose
  7. 7. Introduction  This condition has Led to the development of monograms and equations designed to estimate optimal digoxin dosage.  Equations Based on the most important pharmacokinetic parameters F & Vd loading dose (LD) CL the maintenance dose & rate (t½) time to steady state & the dosing interval
  8. 8.  understanding the clinical pharmacokinetics of Digoxin will help us to improve in the dosage regimens design and ‘‘therapeutics drugs monitoring’’. Introduction  Incorrect dosage of digoxin occurs frequently and is due in most cases to relative over- or under dosage
  9. 9. Objective  To Describe the profile of digoxin concentration in the body which depend of his absorption, distribution, metabolism and elimination and to give a digoxin dose regimen process through a case study.
  10. 10. I-Pharmacokinetics of Digoxin Absorption  80 % absorbed after oral administration of tablets  75-80 % absorbed after administration of elixir  75-80 % absorbed from liquid filled capsule  80 % absorbed IM but not recommended
  11. 11. I-Pharmacokinetics of Digoxin Absorption: factors affecting bioavailability  40 % degraded by intestinal bacteria 1 in 10  FOOD: high fiber product  DRUGS: Antacids, cholestyramine, kaolin, sulfasalazine, metoclopramide and neomycin reduce bioavailability
  12. 12. 1. serum digoxin concentration–time curve follows a two-compartment model 2. 8-12 hours tissues distribution phase. DIGOXIN LEVELS after IV Dose Distribution I-Pharmacokinetics of Digoxin
  13. 13. DIGOXIN LEVELS after IV Dose Distribution 3. During the distribution phase, digoxin in the serum is not in equilibrium with digoxin in the tissues I-Pharmacokinetics of Digoxin
  14. 14. Distribution  Bound tightly to muscles tissues Vd Correlated well with lean body Tissues , very large distribution volume Vd = 7.3 L/kg x IBW , approximately 475 to 500L  25 % protein bound  Crosses the placenta and enter the breast milk – Pregnancy category C I-Pharmacokinetics of Digoxin
  15. 15.  Less than 10 % undergoes hepatic metabolism  not dependent of the cytochrome P450 system and it is not know to induce or inhibit it  metabolism via stepwise cleavage of the sugar moieties and lactone ring reduction Metabolism I-Pharmacokinetics of Digoxin
  16. 16.  Digoxin Elimination follows first-order kinetics  50-70% is excreted almost entirely unchanged by the kidney  Affected by some drugs interactions & diseases conditions  Half life 36-48 hours and increase in case of renal impairment Elimination I-Pharmacokinetics of Digoxin
  17. 17. Determination of Digoxin dose regimen Factors Units Minimum effective concentration, 0.5 ng/mL Maximum safe concentration 2.0 (CHF*) >2.0 (atrial arrhythmias) ng/mL Bioavailability 0.7 (tablets) 0.80 (elixir) 0.95 (capsule) Disease Factors Euthyroid = 1.0 Hypothyroid = 0.7 Hyperthyroid=1.25 Concurrent Therapy Factors None = 1.0 Quinidine = 0.6 Verapamil = 0.6 CHF Factor None = 1.0 CHF = 0.9 More than one disease or concurrent therapy factor: Use Factor =1.0 Facto r
  18. 18. Digoxin Equation w/ renal dysfunction: Vd = (3.12 x CLcr* + 3.84) CT* x IBW  IBW = 50 (or 45.5) + 2.3 x (inches over 60)  CLdig (L/h)= (0.06 x CHF x CLcr + 0.02) x Factor x IBW  CLcr = ((140 - Age) x IBW) / (72 x SCr) ( x 0.85 for females  Vd = 7.3 L/kg x IBW Determination of Digoxin dose regimen
  19. 19. Digoxin Case WB is a 75-year-old female with PMH including atrial fibrillation, type II diabetes, hypertension, and renal insufficiency. She is 5’4’’tall 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 II- Determination of Digoxin dose regimen
  20. 20. CALCULATE LOADING DOSE (1/3) LD = Vd x Cp/F where Vd = Volume of distribution (liters) Cp = target serum level (mcg/l) F = bioavailability factor • IV push = 1 • capsules= 0.95 • elixir = 0.8 • tablets = 0.75
  21. 21.  WB w/ Renal Dysfunction Vd = (3.12 x CLcr + 3.84) CT x IBW  CLcr = ((140 - Age) x IBW) / (72 x SCr) ( x 0.85 for females) CT = Concurrent Therapy Factors =1 IBW = 45.5 kg + 2.3 (4 in) = 54.7 kg = ((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 CALCULATE LOADING DOSE (2/3)
  22. 22.  WB w/ Atrial fibrillation Target Cpss = 1.0 mcg/L Lanoxin tablets Dose regimen for F = bioavailability factor = 0.75 LD = Vd x Cp/F LD = (246.15 L x 1 mcg) / (0.7) = 351.64 mcg CALCULATE LOADING DOSE (3/3) Use 375 mcg tabs once
  23. 23. CALCULATE MAINTENANCE DOSE (1/3) MD = (Cldig x Cp x tau) / F where Cldig = Digoxin clearance (l/hr) Cp = target serum level (mcg/l) tau = dosing interval (hours) F = bioavailability factor
  24. 24. CALCULATE OF MAINTENANCE DOSE (2/3) Cldig = Digoxin clearance ((140-75) x 54.7 kg (.85)) / (3.4 x 72) = 12.35 mL/min CLcr =  IBW = 54.7 kg 3.37 L/hr Cldig= Cldig = (0.8 ml/min/kg x IBW) + CLcr (0.8 mL/min/kg x 54.7 kg) + 12.35 mL/min = 56.11 mL/mi Cldig= 56.11 mL/min x 0.06 =
  25. 25. Cldig 3.37 L/hr Target Cpss = 1.0 mcg/L tau = 24hours F tablets = 0.7 = MD = (3.37 L/h x 1 mcg/L x 24h ) / 0.7 =115.54 mcg Then Use 125 mcg tabs qday CALCULATE OF MAINTENANCE DOSE (3/3)
  26. 26. Conclusion  Digoxin is a very cheap and effective drug and therefore useful clinically in heart failure  equations designed to estimate optimal digoxin dosage are very useful to avoid under or over dosage  NTI : understanding of the clinical pharmacokinetics useful to prevent digoxin toxicity
  27. 27. References  20th edition top 200 pharmacy drug cards. SFI Medical Publishing. 2004.  Tharp, R. (2006) Digoxin Dosing. : http://www.rxkinetics.com/dig.html  Medicinal Plants. (2006) Digoxin Image. Updated Aug 12, 2005. :http://www.science.siu.edu/plant biology/PLB117/Nickrent.Lecs/Medicine.html  Digoxin Structure. Retrieved March 8, 2006 from world wide web: http://medpharm.chunma.ac.kr/Aldja/CVS/cardiac_glycoside/img/digoxin_st ructure.GIF
  28. 28. Thank you very much For your attention!!!
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Digoxin : Clinical pharmacokinetics Pharmacokinetics (ADME) and Digoxin case study

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