The analgesic effect is to make the cat’s pain disappear. At the same time, because the generation of pain can make the cat restless, behave abnormally, and even engage in aggressive behavior, analgesic drugs also have a sedative effect. The cause of pain may be inflammation of some organs. Lesion, or caused by trauma and collision, pain is mediated by nerves, so most analgesic drugs act on the central system.

Analgesics are divided into two types, mainly opioid analgesics and narcotic analgesics. Narcotic analgesics are drugs that can induce sleep or anesthesia while providing strong analgesia, while opioid analgesics Painkillers can cause sedation and euphoria in cats, and are addictive and dependent. They generally do not cause cats to lose consciousness. These medicines can also be used for analgesia, cough and diarrhea, etc. ​​​​​​

1. Pharmacokinetics

Analgesic drugs have lipophilic properties and quickly penetrate into most tissues. The concentration is higher in the parenchymal tissues of internal organs and lower in muscle and fat. They can be rapidly metabolized into polar metabolites by the liver and other enzyme systems. , most drugs have their maximum effect 30 to 60 minutes after injection, and the duration of action is less than 2 hours in most animals, and the analgesic time occasionally reaches 4 to 5 hours.

2. Pharmacological effects

For the central system, it mainly has an analgesic effect, which can change the feeling and response to pain, thereby relieving severe, especially dull and long-lasting pain. It can make animals sedated, lethargic and confused, but can wake them up. It has an inhibitory effect on the respiratory center and also has an inhibitory effect on the cough center. After taking the drug, the cat's pupils will dilate, and sometimes nausea and vomiting may occur.

Increased saliva secretion, vomiting and defecation, and constipation are often seen due to contracture of the gastrointestinal tract.

3. Some common analgesics

　1. Morphine

This product is commonly used as its hydrochloride, which is white, mercerized needle-like crystals or crystalline powder; odorless; and easily deteriorates when exposed to light. Soluble in water, slightly soluble in ethanol, almost insoluble in chloroform or ether.

Morphine is a powerful analgesic, suitable for acute sharp pain where other analgesics are ineffective, such as severe trauma, war injuries, burns and other pain. , the application of this product can calm animals and reduce the burden on the heart.

Because this product has a strong excitatory effect on smooth muscle, it cannot be used alone for visceral colic (such as biliary colic, etc.), but should be combined with effective antispasmodics such as atropine.

Morphine has a powerful central analgesic effect, a wide range of analgesia, and is effective for all kinds of pain. Morphine-like mania in cats can be avoided by administering small doses multiple times or giving diazepam at the same time.

Morphine also has a powerful antitussive effect and affects the body temperature regulation center, which can lower the cat’s body temperature.rise. Morphine is mainly administered by subcutaneous or intramuscular injection. The general dosage for cats is 0.5~1mg.

　2. Pethidine

Meperidine, also known as meperidine. The pharmacological effects are basically the same as those of morphine. Pethidine is a white crystalline powder, odorless, easily soluble in water or ethanol, soluble in chloroform, and almost insoluble in ether.

The analgesic effect is weaker than that of morphine, its potency is 1/7 to 1/10 of morphine, and its duration of action is shorter than that of morphine, ranging from 2 to 4 hours. The sedative, euphoric, respiratory depression and vasodilatory effects are equivalent to those of morphine.

It can also excite smooth muscles and increase the tension of smooth muscles and sphincter muscles. However, due to its short action time, it is less likely to cause constipation and urinary retention. Large doses of pethidine can also cause bronchial smooth muscle contraction.

It has the effect of slightly stimulating the uterus, but has no effect on the normal contraction of the uterus at the end of pregnancy, and does not oppose the effect of oxytocin, so it does not delay labor.

Pethidine is mainly used for sedative analgesia in cats or as pre-anesthesia administration in cats.

　3. Cyclic hydrohydroxymorphan

It is an agonist antagonist and can be injected intravenously, intramuscularly, subcutaneously and orally. When used in combination with other drugs such as acepromazine, ketamine and xylazine, cyclohydromorphan is more effective than morphine. More than 7 times, it has a very powerful analgesic effect on internal organs, while having a small inhibitory effect on the heart and lungs.

IV. Side effects of analgesics

After using this type of medicine, adverse reactions such as nausea, vomiting, constipation, lung and liver function damage, and urination may occur.