Inventory of several routes of drug excretion

 Usually, good pharmacokinetics properties are one of the criteria for judging a good or bad drug. Pharmacokinetics can explore the absorption, distribution, metabolism, and excretion of drugs in the body, as well as the pharmacological and toxicological significance, brought about in this process, to ensure the safe dose of rational clinical use of drugs, reduce the incidence of adverse reactions in the process of clinical use, and ultimately ensure the safety of human drug use. Among them, drug excretion is an essential component of drug elimination in vivo and is part of the pharmacokinetic study. Generally, drugs are excreted through the kidneys, bile, lungs, breast milk, salivary glands, bronchial glands, sweat glands, and intestines.

1、Renal

The kidney is an essential organ for drug excretion. The basic structure of the kidney is the renal unit, which consists of the glomerulus and the renal tubules, and there are about one million renal units in a kidney. The blood flow through the kidneys is enormous, mainly used to excrete the body's waste, regulate the body's water and osmolarity balance, maintain electrolyte concentration and acid-base balance, and secrete some valuable substances for the body. The drugs taken enter the bloodstream and pass through the circulatory system to all parts of the body, most of which eventually pass through glomerular filtration and are excreted in the urine as prototypes or metabolized into metabolites in the body.

The renal function directly affects the excretion of drugs, and it is because most drugs are excreted from the kidneys and are also most vulnerable to drug injury. Changes in pharmacokinetics can lead to changes in drug exposure and predispose patients to overdose or underdose and subsequent adverse effects or treatment failure. The kidney is an essential organ for drug metabolism and excretion, and the kinetics of drug metabolism can change significantly after the development of kidney disease. Therefore, it is sometimes necessary to consider the effect of renal factors on drug excretion when conducting studies on drug metabolism kinetics.

2、Bile

Drugs can be excreted from the bile, the principle of which is similar to renal excretion but is not the main route of drug excretion. When studying drug metabolism kinetics, the concentration of drugs and their metabolites in the bile needs to be tested. Drugs excreted from the bitterness need a specific chemical structure and a molecular weight of more than 300 to be eliminated. Large molecules or proteins with a molecular weight of more than 5000 are difficult to excrete from the bile. The transport of drugs from hepatocytes to bile is an active transport process, which requires a carrier and saturation. Hepatocytes have at least three transport systems: organic acid transport, organic base transport, and neutral compound transport. There is competitive inhibition of drugs belonging to the same transport system. After the medicine is excreted from the bile into the duodenum, some of it is excreted in the feces, and some of it can be absorbed into the blood by the intestinal epithelium, forming the "hepatic-intestinal circulation."

Pharmacokinetics can quantitatively study the absorption, distribution, metabolism, and excretion patterns of drugs in living organisms and is vital in developing innovative drugs. Medicilon Pharmacokinetics Lab has passed the GLP certification by NMPA/ NMPA. Following the guiding principles of ICH,NMPA and FDA. The lab offers in vivo and in vitro pharmacokinetic tests according to the needs of our clients and provides them with complete sets of pharmacokinetic evaluation and optimization services.

3、Lung

The lungs can excrete gas and volatile drugs with exhalation. Some substances with small molecular weight and low boiling points, such as inhaled anesthetics, dimethyl sulfoxide, and certain metabolic waste gases, can be excreted with pulmonary exhalation.

4、Lactation

The total amount of drugs excreted from breast milk is <2%. Some medicines passed in large amounts from breast milk, such as erythromycin, diazepam, carbamazepine, and sulfisoxazole, are prone to toxic side effects in infants. The drug's concentration gradient, lipid solubility, plasma, milk PH, and molecular weight can all affect the excretion of the drug from breast milk.

5. Salivary gland

Salivary excretion has no clinical significance on drug elimination. Still, the law of relative stability of the ratio of salivary drug concentration to plasma drug concentration can be used to study pharmacokinetics by replacing blood concentration with a salivary concentration of drugs.

In addition, bronchial glands, digestive glands, sweat glands, and intestines are also the excretion pathways of some drugs, and most of the medicines in the feces are drugs that have not been absorbed orally. The drugs that enter the body exert their effects on the organism. On the one hand, the organism constantly transports or changes the drugs. The drugs entering the human body, whether metabolized or not, will eventually leave the body in different forms. Only the excretion rate and excretion pathways are different.