Nicotine levels reach the brain within 7 seconds after a single puff on a cigarette, but peak concentrations can require as long as 4 hours after application of a patch. Chewing gum produces peak plasma concentrations within 15-20 minutes. It crosses the placenta and is secreted in milk. The concentrations of nicotine in amniotic fluid and fetal serum exceed those in maternal serum. Detectable amounts also appear in the serum and urine of infants of smoking, nursing mothers.
Plasma concentrations decline in a biphasic manner.
This may be the result of nicotine's action on the sympathetic nervous system or secondary to release of catecholamines from the adrenal medulla. Tolerance to this effect does not develop. Nicotine use should be discouraged during pregnancy because spontaneous abortions have been reported. Nicotine is classified as FDA category D for the transdermal systems and category X for the gum. Nicotine should not be used during breast-feeding.