S. Balakrishnan
Sponsored Links
This presentation is the property of its rightful owner.
1 / 48

S. Balakrishnan Department of Pharmacology, Pondicherry Institute of Medical Sciences PowerPoint PPT Presentation


  • 81 Views
  • Uploaded on
  • Presentation posted in: General

S. Balakrishnan Department of Pharmacology, Pondicherry Institute of Medical Sciences. Absorption. How long it takes after absorption till drug is detectable? (lag time or t lag ). How long it takes before peak – serum or plasma concentration are achieved (t max ).

Download Presentation

S. Balakrishnan Department of Pharmacology, Pondicherry Institute of Medical Sciences

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


S. Balakrishnan

Department of Pharmacology,

Pondicherry Institute of Medical Sciences


Absorption

How long it takes after absorption till drug is detectable? (lag time or tlag).

How long it takes before peak – serum or plasma concentration are achieved (tmax).

What is the peak serum concentration? (Cmax)


Absorption problems 1

Vomiting patient

Ketoconazole needs acid

Patients on proton pump inhibitors (PPI), H2 blockers

Take with Coca Cola


Absorption problems-2

Quinolones (ciprofloxacin)

Bind to antacids, sucralfate

Solution: PPI or H2 blocker

Didanosine (ddI) unstable in acid; so: antacid in the tablet

Drugs taken with (out) food


Distribution


Changing Vd

Gentamicin distributes into space resembling extracellular fluid (ECF)

ECF larger in shock, drops with recovery

Gentamicin levels lower in shock, rise with recovery


Limited distribution-1

Most antibiotics well distributed, but ...

Not always intracellular

Not always to:

Central nervous system

EyeProstateBone

Placenta Breast milk


Limited distribution-2

Meningitis: Higher doses to get adequate CNS levels

Prostatitis: Prefer trimethoprim-sulfamethoxazole, quinolones


Intracellular penetration

pH- only basic drugs penetrate

Beta lactams ansd AGs- NO

Quinolones and macrolides-YES


Distribution to placenta & breast milk

Hard to predict

Practical matter: look up data on a drug


Plasma protein binding

Unbound drug exerts effect.

Unbound drug diffuses into extra vascular sites.

Slows rate of elimination - & t½ - longer dosing interval.

Significant only if > 80%


Extensive protein binding

“Good”: Allows slow, steady release of heavily bound drug, e.g. ceftriaxone

“Bad”: since less “free” drug available for bacteria, e.g. Ceftriaxone

Reality: Only one factor


Protein binding perinatal issue

Sulfonamide displaces unconjugated bilirubin from serum protein

Perinatally, high unbound bilirubin causes kernicterus & brain damage

Don’t use sulfonamides in 3rd trimester, neonate


Biotransformation

Phase I

Phase II


Biotransformation: CYP 450

Often hepatic microsomal enzymes (CYP 450)

Rates vary up to 6-fold from one person to the next

Enzymes genetically determined


Biotransformation: HIV & TB

Rifampin (for TB) induces CYP450 3A4 & reduces levels of indinavir (for HIV)

Indinavir inhibits CYP450 3A4 & increases levels of rifampin

Solution: Low dose rifabutin, high dose indinavir


Biotransformation: ketoconazole, erythromycin

Ketoconazole, erythomycin inhibit CYP450 3A4

Slows metabolism of cisapride, levels rise, causes torsade de pointes, death

Cisapride highly restricted


Bioavailability

IV to oral switch


Elimination

Renal vs non renal clearance

Elimination t1/2


General concept: Elimination t1/2

Half-life

Time for serum concentration to fall 50%

Constant if a person is stable

Varies from person to person


Concentration- time curve


Extravascularconcentration

Extracellular sites reached via diffusion from blood

Intracellular fluid

Extracellular sites with restrictive barriers

Urine


General concept: Clearance

Quantitative measure of body’s ability to eliminate the drug

Includes various forms of excretion


Antimicrobial concept: MIC, MBC

MIC: Minimum inhibitory concentration (to inhibit growth in vitro)

MBC: Minimum bactericidal concentration (to kill in vitro)

MIC90: Inhibits 90% of strains


Break point

Is in part concentration which can be achieved at the site of infection

Susceptible: MIC < breakpoint

Resistant: MIC > breakpoint


Post-antibiotic effect

Persistence of effect (inhibition of growth or killing) after drug removed (or level below MIC)

“PAE” + pharmacokinetics affects dosing strategy


Post-antibiotic effect

Post antibiotic sub – MIC effects

Post antibiotic – leukocyte effects


Important PK/PD Parameters

Important PK/PD Parameters

8

Time above MIC:

6

Drug A

Drug A

Drug B

4

Drug B

Proportion of the dosing interval when the drug concentration exceeds the MIC

Antibiotic concentration (ug/ml)

2

B

B

0

Time

A

Time above MIC


Important PK/PD Parameters

AUC/MIC

is the ratio of the AUC to MIC

Peak/MIC

is the ratio of the peak concentration to MIC

Area under the curve over MIC

PEAK

Antibiotic concentration

Time


PK/PD and Antimicrobial Efficacy

  • 2 main patterns of bacterial killing

    • Concentration dependent

      • Aminoglycosides, quinolones, macrolides, azalides, clindamycin, tetracyclines, glycopeptides, oxazolidinones

      • Correlated with AUC/MIC , Peak/MIC

    • Time dependent with no persistent effect

      • Beta lactams

      • Correlated with Time above MIC(T>MIC)


Goal of therapy based on PK/PD


Magnitude of PK/PD measures predictive of efficacy for select antibiotic classes versus some pathogens


Aminoglycoside pharmacodynamics in vivo


Vancomycin Outcome vs 24h-AUC/ MIC ratio


Fluoroquinolone PK/PD vs S. pneumoniae


PK/PD of beta-lactams and macrolides in otitis media


Concentration dependent killing….azithromycin

  • 24 hour AUC/ 25-immunocompetent patients

  • 24 hour AUC/ 125- immnocompromised patients

  • 24 hour AUC mg.h/ L -3 mg.h/L

  • Macrolide susceptible S.pneumoniae MIC90 0.12 mg/L

  • H. Influenzae MIC90 1-2mg/L

  • Macrolide resistant S. pneumoniae MIC90 >8mg/L


PK/PD breakpoints of parenteral beta-lactams based on serum concentrations present for >40-50% of dosing regimens shown and MIC90 values of isolates of S. pneumoniae


Dosage Adjustment Needed in Renal Impairment I

Acyclovir ethambutol

aminoglycosides,Penicillins (except antistaph)

aztreonam,Quinolones

cephalosporins (except cefaperazone & ceftriaxone)

clarithromycin,Carbapenems


Dosage Adjustment Needed in Renal Impairment II

daptomycin,Vancomycin

doripenem, emtricitabine,

famiclovir, ertapenem,

flucytosine, ganciclovir,

imipenem, meropenem,

lamivudine, foscarnet,

fluconazole,


C/I in renal failure

Methanamine

Nalidixic acid

Nitrofurantoin

Sulfonamides

Tetracyclines except doxy & minocycline


Dosage adjust in hepatic impairment

Chloramphenicol

Clindamycin

Erythromycin

Metronidazole

Tigecycline


  • Login