Paracetamol: Paracetamol quickly and completely absorbed after oral administration. Absolute bioavailability after oral administration is about 80% and is dose-dependent in the dose range from 5 to 20 mg / kg body weight. It practically does not bind to plasma proteins, and its volume distribution is about 0.91 kg.
After oral administration, the half-life (T1/2) of paracetamol from plasma is about 2.3 hours in healthy adults, varying from 1.5 to 3.0 hours.
Paracetamol undergoes intensive biotransformation in the liver, its main metabolites are inactive phenolsulfate and glucuronide conjugates. The intermediate product of the metabolism of paracetamol is usually excreted by the kidneys in the form of conjugates of mercapturic acid and cysteine. Glutathione conjugate can be excreted with bile, but in this case it is cleaved by intestinal peptidases and the cleavage products are reabsorbed.
Chlorpheniramine maleate: After oral administration, it is almost completely absorbed and distributed in the tissues.The maximum concentrations in the plasma were achieved in 2-3 hours after a single dose on an empty stomach at a dose of 12 mg.
Unchanged chlorpheniramine (35%), as well as monodemethylated (20%) and demodetylated (10%) metabolites were detected in human urine. Chlorpheniramine and its demethylated metabolites are slowly excreted over time.
Dextromethorphan hydrobromide: After oral administration, dextromethorphan is well absorbed, but is subjected to intensive pre-systemic metabolism in the liver, resulting in a plasma concentration of only 0.1 μg / L after 0.5 hours and an average maximum concentration 2.5 hours after a single dose of 20 mg is 1.8 μg / l. Dextromethorphan undergoes intensive metabolism in the liver; about 50% of the dose is excreted by the kidneys within 24 hours. The intestine excretes less than 1% of the dose. About 8% of the dose is excreted unchanged by the kidneys for 6 hours.
Phenylephrine hydrochloride: Absorption of phenylephrine after oral administration varies significantly, it undergoes intensive presystemic metabolism. As a result, its systemic bioavailability is only 40%, and the maximum plasma concentrations are achieved 1-2 hours after ingestion. The volume of distribution is 200-500 liters, and the average T1/2 from the plasma is 2-3 hours.
After absorption phenylephrine is subjected to intensive biotransformation in the intestinal wall. After oral administration, 24% of phenylephrine is deaminated, since most of the ingested drug is metabolized by sulphation even before it reaches the liver.