Pharmacotherapeutic group: Analgesics, opioids, diphenylpropylamine derivatives
ATC code: N02AC03
Piritramide is a pure µ-opioid receptor agonist, which has a slightly less analgesic potency than morphine. Analgesia results from activation of the µ-opioid receptors in the spine and the higher pain centres such as the thalamus and cerebral cortex, thereby raising the pain threshold and the sensitivity to pain. At therapeutic doses, opioid-related undesirable effects e.g. respiratory depression, cardiovascular undesirable effects, disturbance of intestinal motility, nausea and vomiting are less severe.
Clinical studies have shown that piritramide rapidly takes effect. The analgesic effect occurs approx. 1 to 2 minutes after i.v. application, approx. 10 to 15 minutes after i.m. application. After s.c. application a maximum tissue concentration is observed after approx. 30 minutes. The duration of action is approx. 5 to 8 hours.
Peak plasma levels are achieved after 15 minutes following i.m. application.
The protein bond of piritramide is almost 95%. The initial distribution volume after a single bolus is 0.7–1.0 l/kg, and between 4.7 and 6 l/kg in steady-state. The distribution volume after prolonged administration rises to 11.1 l/kg in steady-state.
Piritramide is primarily metabolised in the liver. The structure of its metabolites has as yet to be determined
The plasma elimination half-life is between 4-10 hours. After prolonged administration it rises to 17.4 hours. Following an i.v. bolus clearance is almost 600 ml/min and rises to 1100 ml/min with prolonged administration. Renal clearance is 1.4% of total clearance.
In children aged between 2 months and 4 years the terminal elimination half-life is about 2.7 hours. The distribution volume is 1.7 l/kg in infants aged 2-4 months, rising to almost 7.0 l/kg in children aged 4 months to 4 years. Total clearance is 9.8 ml/kg/min in infants aged 2-4 months and 25 ml/kg/min in children aged 4 months to 4 years. The rise in elimination may necessitate adjustment of the dose.
In acute toxicity studies in rats and mice (i.v., s.c., p.o.) as well as in studies with repeated use up to 3 months in rats (s.c.) and dogs (s.c., i.m.) preclinical effects were only observed at dosages clearly above the maximal human therapeutic dose. In a battery of in-vitro studies piritramide did not show any potential to be mutagenic or clastogenic.
Animal studies are insufficient with respect to reproductive toxicity. It is unknown whether piritramide is crossing the placental barrier or passes into breast milk. Studies in rats and rabbits did not give any evidence for embryotoxic or teratogenic effects (NOAEL 2.5 mg/kg). Studies for peri-post-natal development and fertility are not available.
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