Pregnancy: Other considerations
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In particular, drug pharmacokinetics will change in the mother. For example increases in plasma volume result in lower serum concentrations of drugs that are predominantly held in the plasma, that is those with a low volume of distribution (e.g. aspirin, phenytoin). A reduction in serum albumin concentrations may result in higher levels of the free fractions of some protein bound drugs (e.g. phenytoin, diazepam). Increases in renal function may affect the clearance of drugs excreted by the kidney (e.g. ampicillin, gentamicin).
It is important to remember that some of these parameters will quickly revert back to their pre-pregnancy levels and that dose adjustments may be required soon after delivery. For example the changes in drug metabolism that require lamotrigine doses to be significantly increased during pregnancy rapidly return to normal postpartum, requiring close monitoring and prompt dose reductions to avoid toxicity.
When advising on a medicine for use in pregnancy don’t forget the 'normal' contraindications and precautions as they apply to the mother (e.g. avoid recommending labetalol for hypertension in a pregnant patient with asthma). Preventable side effects from medication can reduce maternal compliance, but major side effects might also threaten the fetus.
Finally, note that all women should take folate supplements from the time pregnancy is planned and for the first 12 weeks of pregnancy to reduce the risks of neural tube defects in the fetus. Most women should take 400 micrograms daily, but there are exceptions. For example, women taking antiepileptic medication, those on proguanil for malaria prophylaxis, and women who have previously had a child with neural tube defects should take 5mg daily.
You can read more about folic acid use in pregnancy on the bumps website and read about other dietary advice in pregnancy on the NHS website.
Paternal exposure to medicines
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- Does the medicine have the potential to alter the number or structure of chromosomes, the genetic sequence or cause epigenetic modification of the DNA?
- Can the medicine affect spermatogenesis, sperm viability, motility or morphology?
- Can the medicine cause sexual dysfunction such as erectile dysfunction or loss of libido?
Most medicines probably don’t pose a significant risk but there are exceptions including cytotoxic agents. If a patient has been exposed to such a medicine then in theory he should wait 6 months (2 spermatogenic cycles) before conception is planned.
It is theoretically possible that fetal exposure to a drug or its active metabolites may occur through