Distribution during pregnancy

Distribution during pregnancy

Once a woman is pregnant, physiological changes can occur that will effect drug distribution. Most notably, there can be an increase in total body water of up to 50%. This is due to the growth of the uterus, fetus, placenta and amniotic fluid. The total body fluid increases with 20%, which is about 1200 - 1600ml above non-pregnant women. In addition, regional blood flow increases: the blood flow through kidneys, skin and mammary gland is increased. The blood flow through the uterus increases even until 20% of the cardiac output at term. Skeletal muscle blood flow is decreased.

Another important determinant for drug concentration

in the plasma is the albumin binding. During pregnancy there is a decrease in albumin concentration. Therefore, the albumin binding decreases.

Therefore, if we use the same example with 10 units of drug, an additional 3 units distribute into other fluids and now only three remain in the plasma. Also, only 1 of these 3 units (30%) are bound to albumin. The drug is also distributed through the system at a greater flow rate of Q.

The changes in body composition have an impact on distribution of certain drugs. The volume of distribution of hydrophilic drugs will be increased and thus dose adjustments are needed.

1

During pregnancy the plasma proteinbinding of many drugs is reduced in the mother's plasma. This is caused by: