From Academic Kids

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Chemical structure of pethidine.

Empiric formula C15H21NO2
Molecular weight 247.33
Bioavailability 50%
Metabolism Liver
Elimination half life 3-8 h
Excretion Urine
ATC code N02AB02
Pregnancy category ? (USA)
C (Aus)

Pethidine (INN) or meperidine (USAN) (also referred to as: isonipecaine; lidol; operidine; pethanol; piridosal; Algil®; Alodan®; Centralgin®; Demerol®; Dispadol®; Dolantin®; Dolestine®; Dolosal®; Dolsin®; Mefedina®) is a fast-acting opioid analgesic drug. It is used to deal with moderate to severe pain, and is delivered as hydrochloride as tablets, as a syrup or by intramuscular injection. Because pethidine has the potential to be both physically and psychologically habituating, it is important that it be used in only the doses prescribed, and that withdrawal from the drug be supervised by a physician to ensure there are no adverse reactions.


Mode of action

Main article: opioid

Pethidine has effects similar to morphine, but has very little effect on cough or diarrhea. It also tends to cause restlessness instead of sedation. Pethidine's analgesic effect is more rapid than morphine's, but shorter (2-4 hours). In addition, it has a slight antimuscarinic effect.


Pethidine is quickly hydrolysed in the liver to pethidinic acid and is also demethylated to norpethidine, which is more toxic than pethidine, due to its convulsant and hallucinogenic effects. Pethidine's metabolites are further conjugated with glucuronic acid and excreted into the urine.


Pethidine interacts with a number of other medications, including muscle relaxants, antidepressants, benzodiazepines, and alcohol. It is especially dangerous to use if the patient is using monoamine oxidase inhibitor (MAOI) type antidepressants. Such patients may suffer convulsions and hyperthermia. This may be due to inhibition of an alternative metabolic pathway, which leads to increased production of norpethidine. The patient using pethidine should not take any medicine not first cleared with a physician. Pethidine is also contraindicated for use when a patient is suffering from gallbladder, liver, or kidney disease, has a history of seizures or epilepsy, has an enlarged prostate or urinary retention problems, or suffers from hyperthyroidism, asthma, or Addison's disease.

Adverse effects

Main article: opioid

Users of pethidine may experience serious side effects. These include asthma, swelling of the mucous membranes of the nose and throat, swelling of the lips, tongue, or face, seizures, cold and clammy skin, or dizziness and possible unconsciousness. The presence of any of these side effects is an indicator to stop using pethidine immediately and seek immediate medical attention.

Less serious side effects include constipation, dry mouth, lightheadedness, itchiness, muscular twitches, and nausea.


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