Source: Medicines & Healthcare Products Regulatory Agency (GB) Revision Year: 2020 Publisher: Napp Pharmaceuticals Limited, Cambridge Science Park, Milton Road, Cambridge, CB4 0GW
Pharmacotherapeutic group: natural opium alkaloid
ATC code: NO2AA03
Like morphine, hydromorphone is an agonist of mu receptors. The pharmacological actions of hydromorphone and morphine do not differ significantly. The oral analgesic potency ratio of hydromorphone to morphine is approximately 5-10:1. Hydromorphone and related opioids produce their major effects on the central nervous system and bowel. The effects are diverse and include analgesia, drowsiness, changes in mood, respiratory depression, decreased gastrointestinal motility, nausea, vomiting and alteration of the endocrine and autonomic nervous system.
See section 4.4.
In vitro and preclinical studies indicate various effects of natural opioids, such as morphine, on components of the immune system: the clinical significance of these findings is unknown. Whether hydromorphone, a semisynthetic opioid, has immunological effects similar to morphine is unknown.
Hydromorphone is absorbed from the gastrointestinal tract and undergoes pre-systemic elimination resulting in an oral bioavailability of about 32%.
Plasma protein binding of hydromorphone is low (<10%). This percentage remains constant up to very high plasma levels of approximately 80 ng/ml, which are only very rarely achieved with very high hydromorphone doses.
Hydromorphone is metabolised by direct conjugation or reduction of the keto group with subsequent conjugation. Hydromorphone is primarily metabolised to hydromorphone-3-glucuronide, hydromorphone-3-glucoside and dihydroisomorphine-6-glucuronide. Smaller portions of the metabolites dihydroisomorphine-6-glucoside, dihydromorphine and dihydroisomorphine have also been found. Hydromorphone is metabolised via the liver; a smaller portion is excreted unchanged via the kidneys.
Hydromorphone metabolites were found in plasma, urine and human hepatocyte test systems. There are no indications to hydromorphone being metabolised in vivo via the cytochrome P 450 enzyme system. In vitro, hydromorphone has but a minor inhibition effect (IC50 > 50 ΞM) on recombinant CYP isoforms, including CYP1A2, 2A6, 2C8, 2D6 und 3A4. Hydromorphone is therefore not expected to inhibit the metabolism of other active substances which metabolise via these CYP isoforms.
Hydromorphone was non-genotoxic in a bacterial mutation test, in the in vitro human lymphocyte chromosome aberration assay and the in vivo mouse micronucleus assay but positive in the mouse lymphoma assay with metabolic activation. Similar findings have been reported with other opioid analgesics. Long term carcinogenicity studies have not been performed.
No effects have been observed on male or female fertility or sperm parameters in rats.
Hydromorphone was not teratogenic in pregnant rats nor rabbits given oral doses during the major period of organ development. Evidence of a teratogenic effect in mice and hamsters has been reported in the literature.
In a rat pre- and post-natal study, there was an increase in pup mortality and reduced body weight gain in the early postnatal period, associated with maternal toxicity. No effects on continued pup development or reproductive performance were observed.
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