Consumption of nicotine across the globe has a varied way of its absorption in the body. Nicotine, being a weak base, is absorbed readily through the lungs, skin, nasal mucosa, oral, and gastrointestinal tract. Consumption of this drug highly depends on the smoking behavior of the user. Nicotine obtained from tobacco smoke is absorbed by the lungs, leading to an increased concentration of nicotine in the blood. The use of nicotine through nasal sprays leads to a rise in the amounts of the drug in the bloodstream.
Distribution of nicotine happens at certain volumes in adults of 1.7 to 3.0 kg-1. Plasma concentrations of nicotine appear to decrease in a biphasic manner. It is distributed to the lungs, brain, heart, adrenals, spleen, saliva, kidney, skeletal muscle, and thymus. During pregnancy, this drug is spread to placental tissue, fetal blood, amniotic fluid, fetal tissues, and breast milk (Voos et al., 2019). Passive diffusion plays a major role in the penetration of this drug through biological membranes.
Metabolism of nicotine in the body happens first in the liver through first-pass metabolism. Kidneys and the lungs can metabolize nicotine too but to a smaller extent. Nicotine is metabolized majorly into cotinine which is 70-80 percent. Nicotine-1-N-oxide becomes a minor metabolite of the drug with four -seven percent. Bacteria flora reduces nicotine-1-N-oxide to nicotine in the large intestine (Voos et al., 2019). Nicotine is excreted rapidly in the urine with approximately 5-20 percent of absorbed nicotine unchanged during the excretion. The amount of excretion depends on the pH of the urine. Admittedly, nicotine has a different manner of absorption depending on the way it is introduced into the bloodstream just like its distribution and excretion as discussed.
Reference
Voos, N., Goniewicz, M. L., & Eissenberg, T. (2019). What is the nicotine delivery profile of electronic cigarettes? Expert Opinion on Drug Delivery, 16(11), 1193-1203.