Premedication principles and drug used for it
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Premedication - Principles and Drugs
Definition
Premedication refers to the administration of drugs before anesthesia and surgery to achieve specific therapeutic goals. The term is broader than simple sedation - it encompasses any medication given in the preoperative period, including anxiolytics, analgesics, antiemetics, antacids, and antisialagogues.
"Premedication should be given purposefully, not as a mindless routine." - Morgan and Mikhail's Clinical Anesthesiology, 7e
Goals / Principles of Premedication
| Goal | Rationale |
|---|---|
| Anxiolysis | Reduce preoperative fear and anxiety |
| Sedation | Calm the patient; reduce sympathetic stimulation |
| Amnesia (anterograde) | Prevent recall of unpleasant pre/intraoperative events |
| Analgesia | Pre-emptive pain control; reduce intraoperative analgesic requirement |
| Antisialagogue effect | Reduce oral/airway secretions (important for airway manipulation) |
| Vagolysis | Prevent reflex bradycardia |
| Antiemesis | Reduce postoperative nausea and vomiting (PONV) |
| Aspiration prophylaxis | Raise gastric pH and reduce gastric volume in at-risk patients |
| Reduction of anesthetic requirement | Decrease MAC of inhalational agents |
| Antibiotic prophylaxis | Reduce surgical site infection risk |
Note: Sedative premedication has become less common in modern practice, especially with same-day admission and day-case surgery. However, premedication for aspiration prophylaxis, antiemesis, and analgesic purposes remains standard. - Scott-Brown's Otorhinolaryngology, Vol. 1
Drug Classes Used for Premedication
1. Benzodiazepines (Most Commonly Used)
These are the most frequently used premedication drugs. They provide anxiolysis, sedation, anterograde amnesia, and some anticonvulsant effect. They do NOT affect retrograde memory.
| Drug | Route | Dose | Notes |
|---|---|---|---|
| Midazolam | Oral / IV | Adults: 7.5-15 mg oral; 1-2 mg IV. Children: 0.2-0.5 mg/kg oral | Most commonly used benzodiazepine for premedication in both adults and children. Rapid onset, shorter duration |
| Diazepam | Oral | 5-10 mg | Used for anxiolysis; longer duration |
| Lorazepam | Oral / IV | 2-4 mg oral (2 hours preop) | Used when prolonged intense anxiolysis is needed (e.g., cardiac surgery). Duration of amnesia is less predictable |
| Temazepam | Oral | 10-20 mg | Short-acting, popular in day surgery. Give 1 hour before surgery |
| Alprazolam | Oral | Comparable to midazolam | Reduces anxiety without causing amnesia; some psychomotor impairment |
Key point: Midazolam has minimal effects on respiration at standard doses. Benzodiazepines show synergistic respiratory depression when combined with opioids - use with care. Dose reduction needed in elderly patients. - Miller's Anesthesia, 10e
2. Opioids
Used to provide preoperative analgesia and to reduce intraoperative analgesic requirements. In current practice, their routine use has decreased but they remain useful in:
- Patients who are already in pain preoperatively
- Cardiac anesthesia (where heavy premedication was traditionally used)
- Anticipated difficult/awake intubation combined with an antisialagogue
| Drug | Route | Indication |
|---|---|---|
| Morphine | IM / IV | Classic premedication agent (historical); used in cardiac anesthesia |
| Fentanyl | IV | Used intraoperatively for blunting laryngoscopy response; midazolam + fentanyl common in cardiac surgery |
| Remifentanil | IV | For intraoperative analgesia in hypertensive patients |
3. Anticholinergics (Antisialagogues)
Historically combined with morphine derivatives. Now mainly used when excessive secretions are anticipated (e.g., before fiber-optic or difficult intubation).
| Drug | Main Action | Notes |
|---|---|---|
| Atropine | Antisialagogue, vagolytic, bronchodilator | Standard dose 0.01 mg/kg IV for prevention of bradycardia; given preoperatively in certain pediatric cases |
| Glycopyrrolate | Antisialagogue (no CNS penetration) | Preferred when CNS effects of atropine are undesirable |
| Scopolamine (Hyoscine) | Antisialagogue + sedation + antiemetic + amnesia | Used in combination with morphine; also a transdermal antiemetic patch |
4. Aspiration Prophylaxis Drugs
Important in at-risk patients: obesity, diabetes mellitus, renal impairment, GORD, hiatus hernia, pregnant patients, emergency surgery, and full stomach.
| Drug | Class | Mechanism | Notes |
|---|---|---|---|
| Ranitidine | H2 blocker | Reduces gastric acid secretion | Given the evening before and morning of surgery |
| Omeprazole | Proton pump inhibitor | Reduces gastric acid production | Given preoperatively |
| Sodium citrate | Gastric alkalinizer | Neutralizes existing gastric acid | Acts immediately; used for emergency/obstetric cases |
| Metoclopramide | Prokinetic + antiemetic | Increases gastric motility, raises LES tone, reduces gastric volume | Useful in diabetics (delayed gastric emptying) |
"In at-risk patients such as those with diabetes, renal impairment, obesity or GORD, H2 blockers (ranitidine), proton pump inhibitors (omeprazole), gastric alkalinizers (sodium citrate) or prokinetic agents (metoclopramide) may be used." - Scott-Brown's Otorhinolaryngology, Vol. 1
5. Antiemetics (PONV Prophylaxis)
| Drug | Class | Notes |
|---|---|---|
| Ondansetron | 5-HT3 antagonist | Highly effective; given at induction or preoperatively |
| Metoclopramide | D2 antagonist + prokinetic | Dual role: antiemetic + gastric motility |
| Dexamethasone | Corticosteroid | Single dose at induction; reduces PONV and postoperative pain |
| Scopolamine patch | Anticholinergic | Transdermal; applied night before surgery |
| Promethazine | Phenothiazine antihistamine | Older antiemetic agent |
6. Analgesics (Pre-emptive Analgesia)
Oral analgesics given preoperatively are cost-effective and well-absorbed. Evidence that pre-emptive analgesia (giving analgesics before surgical stimulus) is superior to postoperative initiation is weak, but it is widely practiced.
| Drug | Notes |
|---|---|
| Paracetamol (Acetaminophen) | Safe, effective; can be given orally or rectally preoperatively |
| NSAIDs (ibuprofen, diclofenac, celecoxib) | Used with caution - avoid in elderly, those with renal impairment, dyspeptic symptoms, or in surgeries with bleeding risk (altered platelet function) |
| Pregabalin / Gabapentin | Used in multimodal analgesia; reduces opioid consumption postoperatively |
7. Contrast Media Premedication (Special Context)
For patients with known allergy to contrast agents:
- Corticosteroids (e.g., methylprednisolone) + antihistamines - given as a premedication regimen 12-13 hours before the procedure
- No known regimen completely eliminates risk of severe reactions - Campbell Walsh Wein Urology
Special Considerations
Elderly patients:
- Benzodiazepine effects are more pronounced - reduce doses and titrate carefully
- Avoid over-sedation
Pediatric patients:
- Oral midazolam (0.5 mg/kg, 30 min before induction) is the most common premedication
- Non-pharmacological approaches (distraction, videos, parental presence) can be equally effective
Cardiac surgery patients:
- Heavier premedication traditionally used (lorazepam ± morphine)
- Midazolam + fentanyl used during arterial line placement before induction
- Caution in patients with low cardiac output / severe pulmonary hypertension - avoid oversedation
Day surgery / ambulatory patients:
- Sedative premedication now uncommon due to recovery concerns
- Meta-analyses show anxiolytic premedication does NOT significantly delay discharge
- Prefer intravenous midazolam given just before induction rather than long-acting oral agents
Summary Table: Premedication Drug Quick Reference
| Drug | Class | Goal |
|---|---|---|
| Midazolam | Benzodiazepine | Anxiolysis, amnesia, sedation |
| Lorazepam | Benzodiazepine | Prolonged anxiolysis (cardiac surgery) |
| Temazepam | Benzodiazepine | Short anxiolysis (day surgery) |
| Morphine / Fentanyl | Opioid | Analgesia, reduce anesthetic requirement |
| Atropine | Anticholinergic | Antisialagogue, vagolysis |
| Glycopyrrolate | Anticholinergic | Antisialagogue (no CNS effects) |
| Scopolamine | Anticholinergic | Antisialagogue + amnesia + antiemetic |
| Ranitidine / Omeprazole | Antacid | Aspiration prophylaxis |
| Sodium citrate | Antacid | Immediate acid neutralization |
| Metoclopramide | Prokinetic | Reduces gastric volume + antiemesis |
| Ondansetron | 5-HT3 antagonist | PONV prophylaxis |
| Dexamethasone | Corticosteroid | PONV + analgesia |
| Paracetamol / NSAIDs | Analgesics | Pre-emptive analgesia |
Sources:
- Miller's Anesthesia, 10e, Chapters 21 and 27
- Morgan and Mikhail's Clinical Anesthesiology, 7e, Chapters on Preoperative Assessment and Premedication
- Scott-Brown's Otorhinolaryngology Head & Neck Surgery, Vol. 1
- Katzung's Basic and Clinical Pharmacology, 16e, Chapter 25
- Barash, Cullen, and Stoelting's Clinical Anesthesia, 9e
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