1 TDM in individualizacija TDM in individualizacija odmerjanja zdravil odmerjanja zdravil Iztok Grabnar Iztok Grabnar Terapevtski cilji Terapevtski cilji Izbor zdravila in Izbor zdravila in re re ž ž ima odmerjanja ima odmerjanja Spremljanje terapevtskih in toksičnih učinkov FK FD Na Na č č rtovanje terapije z zdravili rtovanje terapije z zdravili Spremljanje terapije z zdravili Spremljanje terapije z zdravili 1. Klinični učinki Indikacija ↑ odmerek ↓ odmerek Znaki toksičnosti F F u u r r o o semid semid Srčno popuščanje ↑ Edemi Motnje elektrolitov Hipotenzija Dehidracija K K arbidopa arbidopa /DOPA /DOPA Parkinsonizem Slaba kontrola Diskinezije Zmedenost simptomov Depresija Tiopent Tiopent al al Anestezija Nezadostna Pregloboka Zastoj anestezija anestezija dihanja
13
Embed
TDM in individualizacija odmerjanja zdravilne_farmakokinetike... · 1 TDM in individualizacija odmerjanja zdravil Iztok Grabnar Terapevtski cilji Izbor zdravila in režima odmerjanja
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
1
TDM in individualizacija TDM in individualizacija odmerjanja zdravilodmerjanja zdravil
Iztok GrabnarIztok Grabnar
Terapevtski ciljiTerapevtski cilji
Izbor zdravila in Izbor zdravila in rerežžima odmerjanjaima odmerjanja
Spremljanje terapevtskih in toksičnih učinkov
FK FD
NaNaččrtovanje terapije z zdravilirtovanje terapije z zdravili
Spremljanje terapije z zdraviliSpremljanje terapije z zdravili1. Klinični učinki
VVarfarinarfarin TE zapleti visok INR nizek INR krvavitve
TTiiroroksksinin Hipotiroidizem nizek TSH visok TSH hipertiroidizem
StatinStatin Zvišan holesterol ↑AST/CK visok hol. miopatija
Spremljanje terapije z zdraviliSpremljanje terapije z zdravili2. Merjenje terapevtskih učinkov in vitro
Spremljanje terapije z zdraviliSpremljanje terapije z zdravili3. Merjenje koncentracije učinkovine
•Kvantitativni odnos med koncentracijo učinkovine in terpevtskimi in toksičnimi učinki•Plazemska koncentracija slabo korelira z odmerkom•Visoko tveganje za terapevtski neuspeh (izostanek terapevtskih učinkov ali toksičnost)*
* Terapevtski neuspeh:
(1) Nizek terapevtski indeks
(2) Visoka variabilnost v farmakokinetiki
- nasitljiva eliminacija- genetski dejavniki (slabi metabolizatorji)- sočasna obolenja- sočasna terapija z drugimi zdravili (interakcije)
Komplianca!
The uses of monitoring are
• to assess adherence to therapy
• to individualize therapy
• to diagnose toxicity
• to guide withdrawal of therapy
• to determine whether a patient is already taking a drug before starting therapy (eg theophylline in an unconscious patient with asthma)
• in research (eg to monitor for drug interactions in post-marketing surveillance using population pharmacokinetics).
TherapeuticTherapeuticRangeRange
Repeated Drug Dosing to Maintain SS LevelsRepeated Drug Dosing to Maintain SS LevelsWithin a Therapeutic RangeWithin a Therapeutic Range
•Lower limit set by the drug level giving perhaps 50% of the maximum therapeutic effect.
•The upper limit is defined by toxicity NOT therapeutic effect and is the level causing toxicity in <5-10% patients.
3
TDM: AminoglycosidesTDM: Aminoglycosides
• Monitoring is mandatory in ALL patientsAG accumulate in the renal cortex to levels 100-fold > plasma
>95% of AG are cleared by glomerular filtration
•Toxicity manifests as:
•NEPHROTOXICITY (Proximal tubule)
•OTOTOXICITY (Hair cells)
Targets for IV GENTAMICINTargets for IV GENTAMICINConventional dosingConventional dosingpeak 30-60 min post-dose = 5-10 mg/L ) BUT toxicity can emerge below these levelsTrough before next dose < 2 mg/L ) if loop diuretics co-administered
Extended interval dosingExtended interval dosingpeak 30-60 min post-dose = 20-30 mg/L )Trough before next dose < 1 mg/L ) If impaired renal function either REDUCE DOSE or INCREASE DOSE INTERVAL(in anephric patients creatinine clearance = 0 : adjustment, knr/kr = 1/20 so …dose reduced to 0.25mg/kg/d or interval increased to 160h)
TDM: Anticonvulsants (PHENYTOIN)TDM: Anticonvulsants (PHENYTOIN)•Therapeutic range - 40-80μmol/L (NB total drug)
Hypoalbuminaemia and urea both ↑ the free fraction
•Toxicity - manifests as nystagmus, ataxia and confusion(dose-dependent in that order)
Extensive but saturable hydroxylation in the liver I.e. switches from zero to 1st order elimination within the TR - ‘apparent’ t1/2may rise from 10-15h to >150h *
* dose increments within the TR should be no more than 25-50mg
Mild P450 inducer and will increase clearance of:warfarin, dexamethasone, cyA and pethidine.
Alteration in ClearanceAlteration in Clearance increased decreased
• Toxicity - manifest as tachyarrythmias, vomiting & convulsions.
• PK problems - Bioavailability varies widely between preparations and lower in MR formulations given PM vs. AM. Non-linear CL: 90% eliminated by the liver & 10% unchanged in the urine (reversed ratio in neonates) I.e.No adjustment for renal failure required but ↓ dose in presence of impaired hepatocellular function.
Whenever possible establish drug level before administering IV andif in doubt do not give bolus loading dose.
TDM: LithiumTDM: LithiumTherapeutic range 0.6-1.2 mmol/L NB at plateau (pre-dose) & avoid Li-heparin tubes!
Toxicity - signs as a guide - TR: fine tremor especially at dosing peak- moderate intox (1.5-3): coarse tremor, ataxia & diarrhoea- severe intoxication (>3): confusion & fits
PK problems Complete absorption - SR formulations to reduce peak levels.>95% excreted by the kidney - initial t1/2 12hbut terminal t1/2 much longer ⇒
70-80% reabsorbed in PCT with no distalreabsorption (unlike Na) ∴PCT retention (hence toxicity risk ) is ↑ by:• reduced exchangeable Na from any cause• loop or thiazide diuretics• NSAIDs or ACEIs.
Special problems Pregnancy - Dose requirements increase due to ↑ renal clearance. Li is also teratogenic and excreted in breast milk
Severe intoxication - usually requires dialysis but because of slow clearance from some compartments rebound rises in Li levels may necessitate repeated HD.
4
TDM: DigoxinTDM: Digoxin• Therapeutic range 1-2ng/L (taken >6h post-dosing; 1ng/L=1.3nmol/L) for inotropic effect not AF.
• Toxicity - may be nonspecific eg nausea, vomiting, abdo pain & confusion but remember bradycardia with increasing of heart block especially with AV junctional escape rhythms and visual disturbance (xanthochromia).
• PK problems - 10% population have enteric bacterium (E. lentum) that can metabolize digoxin. Large volume of distribution (≈ 5L/kg lean BW) and predominexcreted unchanged in the urine with CL∝ GFR.
PK ↑ Vd and CL Thyrotoxicosis/T4↓ Vd and/or CL Verapamil, amiodarone, propafenone↑ absorption Erythromycin, omeprazole↓ absorption Exchange resins, kaolin↓ GFR Any cause of renal impairment/Cyclosporine
PD increase block Hypokalaemia/Kaluretic diureticsof the Na pump
Enzyme Induction/inhibition by Anticonvulsants:Enzyme Induction/inhibition by Anticonvulsants:
•• je opis povezave med fiziologijo je opis povezave med fiziologijo /patofiziologijo in farmakokinetiko /patofiziologijo in farmakokinetiko /farmakodinamiko/farmakodinamiko
Kaj je ?Kaj je ? Enoprostorni farmakokinetiEnoprostorni farmakokinetiččni modelni modelDolgotrajna intravenska infuzijaDolgotrajna intravenska infuzija
...the most probable value of unknown quantities will be that in which the sum of squares of the differences between the actually observed and computed values multiplied by numbers that measure the degree of precision is a minimum...
( ) ( )( )2
1∑=
−→m
jjjjWLS t,ytzwminˆ αα
Johann Carl Friedrich Gauss (1777Johann Carl Friedrich Gauss (1777--1855)1855)
Graphical illustration of the statistical model used in NONMEM for the special case of a one compartment model with first order absorption. (Vozeh et al. Eur J Clin Pharmacol 1982;23:445-451)
11
4321 ΘΘΘΘ=Θ
333213
322223
312111
ωωωωωωωωω
=Ω
332313
322212
312111
σσσσσσσσσ
=Σ
Mean, expected value, or some other point estimate:
Variability among subjects around that mean:
Residual (unexplained) variability and/or model misspecification:
Responses on data input requirements from a questionnaire survey of producers of software for population pharmacokinetic-pharmacodynamic analysis
Program Nature of input, Constraints Dosing histories specified in a flexible manner How is covariate information specified?
BUGS ASCII, S-Plus data set User has to supply code Variable in data set
MIXNLIN SAS data set User has to supply code Classified as inter- and intra-individualNone, but must conform to covariates SAS conventions
NLINMIX SAS data set User has to supply code Variables in the SAS data set
NLME ASCII, spreadsheets and data bases User has to supply code Variables in the data set
NLMIX ASCII, user responsible for writing input routine User has to supply code As for input
NONMEM ASCII Yes (specified by the routine PREDPP) Variables in the data set None (some dimensions areinitially set but these may bechanged by the user)
NPEM ASCII via USC*PACK program Yes Either linked to a pharmacokinetic99 days of time, 99 doses, or numerical value. Interpolation99 values of dependent between covariate values is possiblevariables (maximum of 6)
NPML ASCII User has to supply code Variables in the data set
PPHARM Dedicated data base ASCII Yes Variables in data base or in ASCII file
3. 3. IdentiIdentifikacijafikacija dejavnikov s katerimi lahko dejavnikov s katerimi lahko povepovežžemo intersubjektno variabilnostemo intersubjektno variabilnost