Chapter 14 Pharmacology Flashcards
Mechanisms of Placental Drug Transfer
-Ultrafiltration
-Simple Diffusion
-Facilitated Diffusion
-Active Transport
The placenta acts as a semipermeable membrane with maternal hydrostatic forces pushing drugs with low molecular weight through to the fetal side.
Ultrafiltration
Substances readily passing through the placenta to the fetus as a result of a concentration gradient existing between the fetus and the mother.
Simple Diffusion
When the transfer of drugs across the placenta is aided by proteins.
Facilitated Diffusion
When the drug is moved across the placental membranes against the concentration gradient.
Active Transport
Drug transfer across the placenta is determined by the following 4 factors:
-The concentration difference across the placenta
-The lipid solubility of the drug
-The degree of ionization of the drug
Drugs that cause physical or mental developmental abnormalities
Teratogens or Teratogenic substances
The effects of Teratogens are dependent on several factors:
-The dose of the drug that reaches the fetus or embryo
-The length of exposure to the teratogen
-The gestational age of the fetus at time of exposure
-Other drugs taken concurrently by the mother
Which trimester is the most critical time for teratogens to have an effect?
The first trimester
The process by which a drug enters the body and is distributed throughout the system.
Pharmacokinetics
-Absorbtion
-Distribution
-Metabolism
-Excretion
Drugs that readily cross cell membranes are distributed throughout all fluid areas and very rapidly into the heart, brain, liver, kidney and other highly vascularized tissues, have a high affinity to protein.
Lipid Soluble drugs
Gastric pH
At birth Gastric pH is 6 to 8 but falls to 1 to 3 in the first 24 hours after birth.
The way in which a drug enters the body.
Absorption
-Gastrointestinal tract
-Intramuscuar
-Skin
-Intravenous
Following the absorption of a drug, it is distributed into interstitial, cellular and extracellular fluids
Distribution
Binding to serum proteins
Many drug interactions and toxicity reactions occur when drugs compete for binding to serum proteins, which increases the unbound portion of one or more of the drugs being administered.
Volume of distribution
The volume of distribution relates the amount of drug in the body to the plasma concentration.
-This is very important when it comes to calculating dosages.
The changing or alteration of the drug to a different form, either active or inactive
Metabolism
-The primary site where drug metabolism takes place is the liver.
Most drugs are poorly metabolized in the premature infant, the excretion of a drug is the most determining factor in the termination of a drug’s effects.
Excretion
Excretion
The renal function, both glomerular filtration rate and tubular secretion, in preterm and full-term infants is not completely developed at the time of birth.
Excretion
Drugs that are not extensively metabolized and are primarily excreted through the kidneys are eliminated more slowly in premature infants and dosage adjustments must be made.
