Oxycodone concentrations are not predictive of analgesic response, especially in patients previously treated with opioids. The minimum effective concentration varies widely and is influenced by a variety of factors, including the extent of previous opioid use, age and general medical condition. Effective doses in tolerant patients may be significantly higher than in opioid-naïve patients.

Effects on the Central Nervous System (CNS)

The principal therapeutic action of oxycodone hydrochloride is analgesia. Although the precise mechanism of the analgesic action is unknown, specific CNS opioid receptors for endogenous compounds with oxycodone hydrochloride-like activity have been identified throughout the brain and spinal cord and are likely to play a role in the expression and perception of analgesic effects. In common with other opioids, oxycodone hydrochloride causes respiratory depression, in part by a direct effect on the brainstem respiratory centers. Oxycodone and related opioids depress the cough reflex by direct effect on the cough center in the medulla.

Oxycodone causes miosis, even in total darkness.

Effects on the Gastrointestinal Tract And Other Smooth Muscle

Gastric, biliary and pancreatic secretions are decreased by Oxycodone hydrochloride. Oxycodone hydrochloride, like other opioid analgesics, produces some degree of nausea and vomiting which is caused by direct stimulation of the chemoreceptor trigger zone (CTZ) located in the medulla. The frequency and severity of emesis gradually diminishes with time. Oxycodone hydrochloride may cause a decrease in the secretion of hydrochloric acid in the stomach, may reduce motility, while increasing the tone in the antrum of the stomach and duodenum. Digestion of food in the small intestine is delayed and propulsive contractions are decreased. Propulsive peristaltic waves in the colon are decreased, while tone may be increased to the point of spasm. The end result may be constipation. Oxycodone hydrochloride may also cause spasm of the sphincter of Oddi and transient elevations in serum amylase.

Effects on the Cardiovascular System

In therapeutic doses, Oxycodone hydrochloride, produces peripheral vasodilatation (arteriolar and venous), decreased peripheral resistance, and inhibits baroreceptor reflexes. Manifestations of histamine release and/or peripheral vasodilatation may include pruritus, flushing, red eyes, sweating, and/or orthostatic hypotension. Caution should be used in hypovolemic patients, such as those suffering acute myocardial infarction, because oxycodone may cause or further aggravate their hypotension. Caution should also be used in patients with corpulmonale who have received therapeutic doses of opioids.

Endocrine System

Opioid agonists have been shown to have a variety of effects on the secretion of hormones. Opioids inhibit the secretion of ACTH, cortisol, and luteinizing hormone (LH) in humans. They also stimulate prolactin, growth hormone (GH) secretion, and pancreatic secretion of insulin and glucagon in humans and other species, rats and dogs. Thyroid stimulating hormone (TSH) has been shown to be both inhibited and stimulated by opioids.

Immune System

Opioids have been shown to have a variety of effects on components of the immune system in in-vitro and animal models. The clinical significance of these findings is unknown.