Analgesic Drugs in Anesthesia

Study Notes

Analgesic drugs given pre-operatively reduce the required dose of anesthetic agent and improve patient comfort in the immediate postoperative period.
Options used include opioids, paracetamol, and non-steroidal anti-inflammatory drugs (NSAIDs).

Commonly used in the presence of acute severe pain.
Cause variable sedation and cardiorespiratory depression.
Can cause nausea and vomiting, which may outweigh any beneficial effects.
May precipitate bronchospasm or anaphylaxis.
Classifications of opioids:
- Natural Opium Alkaloids: Morphine and Codeine
- Semi-synthetic: Diacetylmorphine (Heroin) and Pholcodeine
- Synthetic Opioids: Pethidine (Mepiridine) and its congeners, Fentanyl and its congeners, and others

1/10th as potent as Morphine, but has similar efficacy.
Produces as much sedation, euphoria, and respiratory depression in equianalgesic dose and similar abuse potential.
Has less spasmodic action in smooth muscles, less miosis, constipation, and urinary retention.
Has a rapid but short duration of action (2-3 Hrs).
Has a vagolytic effect and tachycardia.
Devoid of antitussive action.
Less histamine releases, making it safer in asthmatics.
Pharmacokinetics:
- Well absorbed orally, with bioavailability of 50%.
- Effects appear in 10-15 min after oral absorption.
- On parenteral administration, action lasts for 2-3 Hrs.
- Metabolized in liver, excreted in urine.

Potent ultra-short-acting synthetic opioid.
Given to patients during surgery for pain relief and adjunctive to an anesthetic.
Specific mu-type-opioid receptor agonist, reducing sympathetic nervous system tone, and causing respiratory depression and analgesia.
Opioid activity is antagonized by opioid antagonists such as naloxone.
Analgesic effects are rapid in onset and offset, with effects and side effects being dose-dependent and similar to other opioids.
Most common side effect is hypotension.