PHARMACOKINETICS & PHARMACODYNAMICS

Mario Wilmath

BASIC PK PARAMETERS

LIBERATION

ABSORPTION

DISTRIBUTION

METABOLISM

ELIMINATION

DOSAGE FORM, STABILITY, QUALITY

ROUTE, DOSE

DRUG TARGET, EFFICACY

HALF-LIFE, SAFETY

DURATION, FREQUENCY

Cardiovascular : Lidocaine, procainamide, digoxin

Infectious Disease: Aminoglycosides, vancomycin

Neurology: Phenytoin, carbamazepine, phenobarbital, valproic acid

Oncology: Methotrexate

Pulmonary: Theophylline, aminophylline

Transplant: Cyclosporine, tacrolimus, sirolimus

CLINICAL DRUG MONITORING

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DOSE & DOSING INTERVALS Intravenous: X0 = C0/Vd

Single IV: Ct future = C0* e-ket Ct past = C0 / e-ket

Multiple IV: Dose= (Cp *Vd)(1-e-nkeτ /1-e-keτ)e-ket

Short-term Infusion (0.5 h), Multiple Dosing:

› R0= CL*Cmax{1-e-keτ /1-e-keT} e-ket 1

› Cmin= Cmax*e-ke(τ -T)

Continuous Infusion (1 h): › R0= CL*Cpss*[1-e-keτ]/1-e-keT 1 ] e-ket 1

› Cmin= Cpss*e-ke(τ -T)

› 2R0/(C1+C2) + 2Vd (C1-C2) )/(C1+C2) (t1-t2)

Loading Dose: LD = Vd*Css / SF

Intermittent IV Bolus: Dose/τ = CL*Cp{1-e-keτ/1-e-keT}*e-ke(τ -T)

Maintenance Dose: MD =CL*Css* τ / SF Oral:

› Multidose: Cave steady state = [LD/Vd*(1-e-keτ)]

› Dose = C*(ka-ke)*Vd/SF*ka* (e-ket-e-kat) Steady State: Multiple doses cause term 1-e-nket 1

Ansel. Dosage Forms.

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EMPIRIC DOSING - NOMOGRAMS

DIGOXIN

AMINOGLYCOSIDES

THEOPHYLLINERxkinetics.org

A review of clinical use of theophylline in acute asthma: Factors influencing kinetic disposition and drug interactionsOhnishi, A./Methods Find Exp Clin Pharmacol 2000, 22(4): 253ISSN 0379-0355 Copyright 2000 Prous Science CCC: 0379-0355 DOI: 10.1358/mf.2000.22.4.584459

Loading Dose 25 mg/kgMaintenance Dose 19 mg/kg

VANCOMYCIN

IBW Ht

Creatinine Clearance

PHYSIOLOGIC PARAMETERS FOR INDIVIDUALIZED THERAPY

1. Body Compartment: Central vs Peripheral2. Body Surface Area3. Weight & Body Composition

• Actual body weight – All Tissues• Ideal body weight - Muscle• Adjusted body weight – Intermediate Distribution

4. Adjustments to PK:• Age• Gender• Disease• Food• Drug Interactions

5. Clinical Endpoint, Surrogate Marker, Lab Measures

6. Toxicity

REFERENCES

1. Allen L, Ansel H, Popovich N. Ansel’s Pharmaceutical Dosage Forms and Drug Delivery Systems. Lippincott Williams & Wilkins. Baltimore, MD, USA. 2005.

2. Bauman JL, et al. “A Method of Determining the Dose of Digoxin for CHF in the Modern Era.” Archives of Internal Medicine. Vol 166, Dec 11/25, 2006.

3. Derendorf H, Hochhaus G, Winkler J. “How the Lung Handles Drugs. Pharmacokinetics and Pharmacodynamics of Inhaled Corticosteroids.” Proceedings of the American Thoracic Society, Vol 1. pp 356-363, 2004.

4. Hendeles L, et al. “Food-induced "dose-dumping" from a once-a-day theophylline product as a cause of theophylline toxicity.” Chest 87.6.758 Vol. 87no. 6 758-765. June 1985.

5. DiPiro JT. Concepts in Clinical Pharmacokinetics.6. Hammerlein, et al. “Age-Related Changes in Drug Metabolism and

Effect.” Clinical Pharmacokinetics, Jul:35(1), 1998.7. Tomlin ME. Pharmacology and Pharmacokinetics- A Basic Reader.

Elsavier, 2010. 8. Images as noted and courtesy of Wikipedia Commons

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