Tiêu đề 18. GENERAL PRESCRIBING GUIDELINES FOR PREGNANCY AND BREAST FEEDING.pdf ✅

PHARMD GURU Page 1  Pregnant women may require drug therapy for preexisting medical conditions or for problems associated with their pregnancy.  This patient population may be exposed to drugs or environmental agents that have adverse effects on the unborn.  It is important to understand the principles of drug use in these patients because any drug administered to a pregnant woman may directly harm the developing fetus or adversely influence her pregnancy. FETAL DEVELOPMENT: The effect of drug therapy in pregnancy depends largely on the stage of fetal development during which exposure occurs. 1. Blastogenesis: During this stage (the first 15-21 days after fertilization), cleavage and germ layer formation occur. The embryonic cells are in a relatively undifferentiated stage. 2. Organogenesis: (14-56 days) All major organs start to develop during this period. Exposing the embryo to certain drugs at this time may cause major congenital malformations. 3. Fetal period: (ninth week to birth) At the ninth week, the embryo is referred to as fetus. In this stage the developing fetus may be at risk from exposure to the pharmacological effects of a variety of fetotoxic drugs and microorganisms. PLACENTAL TRANSFER OF DRUGS:  The placenta is formed by the chorionic villi of the embryo and the decidua basalis of the endometrium of the mother.  It is the functional unit between the fetal body and the maternal blood.  The functions of the placenta include nutrition, metabolism, respiration, excretion and endocrine activity to maintain fetal and maternal well being. GENERAL PRESCRIBING GUIDELINES FOR PREGNANCY AND BREAST FEEDING
PHARMD GURU Page 2  In order for a drug to cause a teratogenic or pharmacological effect in the embryo or fetus, it must cross from the maternal circulation to the fetal circulation or tissues. Generally, this passage occurs via placenta.  The placenta is not a protective barrier: The transfer of most nutrients, oxygen, waste products, drugs and other substances occurs via passive diffusion. FACTORS AFFECTING PLACENTAL DRUG TRANSFER:  Molecular weight: Low molecular weight (less than 500 daltons) diffuses freely across the placenta. High molecular weight drugs (5001000 d) cross less easily. Very large molecular wt. drugs eg.heparin do not cross the placental membranes.  pH: Weakly acidic and weakly basic drugs tend to diffuse across the placental membranes.  Lipid solubility: Moderately lipid-soluble drugs easily diffuse across the placental membranes.  Drug absorption: During pregnancy, gastric tone and motility are decreased, which result in delayed in delayed GI emptying time.  Drug distribution: The alteration of volume of distribution is the result of a combination of changes associated with pregnancy, including increased plasma volume and increased cardiac output secondary to an increase in stroke volume and heart rate.  Plasma protein binding the placenta.  Physical characteristics of the placenta: As pregnancy progresses, the placental membranes become progressively thinner, resulting in a decrease in diffusion distance.  Coexistent disease states: Maternal hypertension or diabetics may reduce or enhance placental drug transfer.
PHARMD GURU Page 3 FDA PREGNANCY CATEGORY: The FDA has a categorization of drug risks to the fetus that runs from: Category A (safest) to "Category X" (known danger - do not use). Category A: Category A, Controlled studies in women fail to demonstrate a risk to the fetus in the first trimester (and there is no evidence of a risk in later trimesters), and the possibility of fetal harm appears remote. Category B: Either animal-reproduction studies have not demonstrated a fetal risk but there are no controlled studies in pregnant women, or animal-reproduction studies have shown an adverse effect (other than a decrease in fertility) that was not confirmed in controlled studies in women in the first trimester (and there is no evidence of a risk in later trimesters). Category C: Either studies in animals have revealed adverse effects on the fetus (teratogenic or embryocidal or other) and there are no controlled studies in women, or studies in women and animals are not available. Drugs should be given only if the potential benefit justifies the potential risk to the fetus. Category D: There is positive evidence of human fetal risk, but the benefits from use in pregnant women may be acceptable despite the risk (e.g., if the drug is needed in a life-threatening situation or for a serious disease for which safer drugs cannot be used or are ineffective). Category X: Studies in animals or human beings have demonstrated fetal abnormalities, or there is evidence of fetal risk based on human experience or both, and the risk of the use of the drug in pregnant women clearly outweighs any possible benefit. The drug is contraindicated in women who are or may become pregnant.