Source: Health Products Regulatory Authority (IE) Revision Year: 2020 Publisher: Teofarma S.R.L., Valle Salimbene (PV), Via F. LLI Cervi, 8 CAP 27010, Italy
Paracodin is a centrally-acting anti-tussive. Dihydrocodeine works on the cough centre to lessen the incidence and intensity of coughing fits. Dihydrocodeine inhibits troublesome, unproductive cough but does not impair the expectoration of bronchial mucus. The analgesic action of DHC may be helpful in patients with painful cough. Dihydrocodeine also exerts dose-dependent sedative effects.
Opiates may cause depression of the respiratory centre and thereby reduce its sensitivity to normal respiratory stimuli (CO2 partial pressure in the blood). It depresses the respiratory centre in a dose-dependent fashion.
Opiates increase for instance the tone of gastrointestinal smooth muscle. Thus, the transit time of food through the gastrointestinal tract is prolonged and intestinal peristalsis reduced. Constipation occurs as a result of inhibited peristalsis and defaecation as well as an increase in the tone of the sphincter ani.
Dihydrocodeine is readily absorbed after oral administration, has a duration of action of 4 to 6 hours, is extensively metabolised in the liver and is excreted mainly via the kidney.
The biological availability of dihydrocodeine is three times higher than that of codeine. In comparative studies in healthy volunteers, 35% of the orally-applied dose of dihydrocodeine was eliminatedin the urine in the course of 24 hours. After oral administration of dihydrocodeine, the highest concentration was found in the plasma after 1.7 hours. The elimination half-life was 4 hours.
The metabolism of dihydrocodeine shows important similarities with metabolism of codeine. Dihydrocodeine is also a substrate of the polymorphic enzyme CYP2D6. This enzyme catalyses the conversion of dihydrocodeineto dihydromorphineby the O-demethylation pathway (see section 4.4).
The mean lethal dose (LD50) of dihydrocodeine hydrogen tartrate was determined on mice and rats after oral and
intraperitoneal administration.
The following 24-hour values, related to the base, were obtained:
| Animal | Route | Sex | Dihydrocodeine base LD50 (mg/kg bodyweight) |
|---|---|---|---|
| Mouse | Oral | m/f | 417/544 |
| Rat | Oral | m/f | 139/129 |
| Mouse | Intraperitoneal | m/f | 160/155 |
| Rat | Intraperitoneal | m/f | 69/73 |
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