Pethidine

Pethidine has one-tenth the analgesic potency of morphine. The duration of action is between 2 and 4 h. It has atropine-like actions and
relaxes smooth muscles.The principal metabolite is norpethidine, which can cause fits. In renal failure and after infusions this metabolite can accumulate and cause seizures.

Uses
It may be indicated in controlling pain from pancreatitis, secondary to gallstones, and after surgical procedure involving bowel anastomosis, where it is claimed to cause less increase in intraluminal pressure. It produces less release of histamine than morphine, and may be preferable in asthmatics.

Contraindications
Airway obstruction
Concomitant use of MAOI

Administration
• IV bolus: 10–50mg PRN
  Duration of action: 2–3 hours

• PCAS: 600 mg in 60 ml sodium chloride 0.9%
  IV bolus: 10 mg, lockout 5–10 min

How not to use pethidine
In combination with an opioid partial agonist, e.g.buprenorphine (antagonizes opioid effects)

Adverse effects
Respiratory depression and apnoea
Hypotension and tachycardia
Nausea and vomiting
Delayed gastric emptying
Reduce intestinal mobility
Constipation
Urinary retention
Histamine release
Tolerance
Pulmonary oedema

Cautions
Enhanced sedative and respiratory depression from interaction with:
• benzodiazepines
• antidepressants
• anti-psychotics

Avoid concomitant use of and for 2 weeks after MAOI discontinued (risk of CNS excitation or depression – hypertension, hyperpyrexia,
convulsions and coma) Head injury and neurosurgical patients (may exacerbate ↑ ICP as a result of ↑ PaCO2)

Organ failure
CNS: sedative effects increased
Respiratory: respiratory depression
Hepatic: enhanced and prolonged sedative effect. Can precipitate coma
Renal: increased cerebral sensitivity. Norpethidine accumulates

Renal replacement therapy
No further dose modification is required during renal replacement therapy