Hydromorphone hydrochloride is a pure opioid agonist with the principal therapeutic activity of analgesia. A significant feature of the analgesia is that it can occur without loss of consciousness. Opioid analgesics also suppress the cough reflex and may cause respiratory depression, mood changes, mental clouding, euphoria, dysphoria, nausea, vomiting and electroencephalographic changes. Many of the effects described below are common to this class of mu-opioid agonist analgesics which includes morphine, oxycodone, hydrocodone, codeine and fentanyl. In some instances, data may not exist to distinguish the effects of hydromorphone hydrochloride tablets from those observed with other opioid analgesics. However, in the absence of data to the contrary, it is assumed that hydromorphone hydrochloride tablets would possess all the actions of mu-agonist opioids.
Central Nervous System
The precise mode of analgesic action of opioid analgesics is unknown. However, specific CNS opiate receptors have been identified. Opioids are believed to express their pharmacological effects by combining with these receptors.
Hydromorphone depresses the cough reflex by direct effect on the cough center in the medulla.
Hydromorphone depresses the respiratory reflex by a direct effect on brain stem respiratory centers. The mechanism of respiratory depression also involves a reduction in the responsiveness of the brain stem respiratory centers to increases in carbon dioxide tension.
Hydromorphone causes miosis. Pinpoint pupils are a common sign of opioid overdose but are not pathognomonic (e.g., pontine lesions of hemorrhagic or ischemic origin may produce similar findings). Marked mydriasis rather than miosis may be seen with hypoxia in the setting of hydromorphone hydrochloride tablets overdose.
Gastrointestinal Tract and Other Smooth Muscle
Gastric, biliary and pancreatic secretions are decreased by opioids such as hydromorphone. Hydromorphone causes a reduction in motility associated with an increase in tone in the gastric antrum and duodenum. Digestion of food in the small intestine is delayed and propulsive contractions are decreased. Propulsive peristaltic waves in the colon are decreased, and tone may be increased to the point of spasm. The end result is constipation. Hydromorphone can cause a marked increase in biliary tract pressure as a result of spasm of the sphincter of Oddi.
Hydromorphone may produce hypotension as a result of either peripheral vasodilation or release of histamine, or both. Other manifestations of histamine release and/or peripheral vasodilation may include pruritus, flushing, and red eyes.
Pharmacokinetics and Metabolism
The analgesic activity of hydromorphone hydrochloride is due to the parent drug, hydromorphone. Hydromorphone is rapidly absorbed from the gastrointestinal tract after oral administration and undergoes extensive first-pass metabolism. Exposure of hydromorphone (Cmax and AUC0-24) is dose-proportional at a dose range of 2 and 8 mg. In vivo bioavailability following single-dose administration of the hydromorphone hydrochloride tablet, 8 mg is approximately 24% (coefficient of variation 21%).
Absorption – After oral administration of hydromorphone hydrochloride tablets, 8 mg, peak plasma hydromorphone concentrations are generally attained within 1/2 to 1-hour
Food Effects – In a study conducted with a single 8 mg dose of hydromorphone (2 mg hydromorphone hydrochloride tablets), food lowered Cmax by 25%, prolonged Tmax by 0.8 hour, and increased AUC by 35%. The effects may not be clinically relevant.
Distribution – At therapeutic plasma levels, hydromorphone is approximately 8 to 19% bound to plasma proteins. After an intravenous bolus dose, the steady state of volume distribution [mean (%cv)] is 302.9 (32%) liters.
Metabolism – Hydromorphone is extensively metabolized via glucuronidation in the liver, with greater than 95% of the dose metabolized to hydromorphone-3-glucuronide along with minor amounts of 6-hydroxy reduction metabolites.
Elimination – Only a small amount of the hydromorphone dose is excreted unchanged in the urine. Most of the dose is excreted as hydromorphone-3-glucuronide along with minor amounts of 6-hydroxy reduction metabolites. The systemic clearance is approximately 1.96 (20%) liters/minute. The terminal elimination half-life of hydromorphone after an intravenous dose is about 2.3 hours.
Hepatic Impairment – After oral administration of hydromorphone at a single 4 mg dose (2 mg hydromorphone hydrochloride tablets), mean exposure to hydromorphone (Cmax and AUC∞) is increased 4-fold in patients with moderate (Child-Pugh Group B) hepatic impairment compared with subjects with normal hepatic function. Due to increased exposure of hydromorphone, patients with moderate hepatic impairment should be started at a lower dose and closely monitored during dose titration. Pharmacokinetics of hydromorphone in severe hepatic impairment patients has not been studied. Further increase in Cmax and AUC of hydromorphone in this group is expected. As such, starting dose should be even more conservative. Use of oral liquid is recommended to adjust the dose (see
DOSAGE AND ADMINISTRATION).
Renal Impairment – After oral administration of hydromorphone at a single 4 mg dose (2 mg hydromorphone hydrochloride tablets), exposure to hydromorphone (Cmax and AUC0-48) is increased in patients with impaired renal function by 2-fold in moderate (CLcr = 40 to 60 mL/min) and 3-fold in severe (CLcr less than 30 mL/min) renal impairment compared with normal subjects (CLcr > 80 mL/min). In addition, in patients with severe renal impairment hydromorphone appeared to be more slowly eliminated with longer terminal elimination half-life (40 hr) compared to patients with normal renal function (15 hr). Patients with moderate renal impairment should be started on a lower dose. Starting doses for patients with severe renal impairment should be even lower. Patients with renal impairment should be closely monitored during dose titration. Use of oral liquid is recommended to adjust the dose (see
DOSAGE AND ADMINISTRATION).
Pediatrics – Pharmacokinetics of hydromorphone have not been evaluated in children.
Geriatric – Age has no effect on the pharmacokinetics of hydromorphone.
Gender – Gender has little effect on the pharmacokinetics of hydromorphone. Females appear to have higher Cmax (25%) than males with comparable AUC0-24 values. The difference observed in Cmax may not be clinically relevant.
Pregnancy and Nursing Mothers – Hydromorphone crosses the placenta. Hydromorphone is also found in low levels in breast milk, and may cause respiratory compromise in newborns when administered during labor or delivery.
Analgesic effects of single doses of hydromorphone hydrochloride oral liquid administered to patients with post-surgical pain have been studied in double-blind controlled trials. In one study, both 5 mg and 10 mg of hydromorphone hydrochloride oral liquid provided significantly more analgesia than placebo. In another trial, 5 mg and 10 mg of hydromorphone hydrochloride oral liquid were compared to 30 mg and 60 mg of morphine sulfate oral liquid. The pain relief provided by 5 mg and 10 mg hydromorphone hydrochloride oral liquid was comparable to 30 mg and 60 mg oral morphine sulfate, respectively.