# 1) Receptor-level action → clinical effects
**Primary (dual mechanism):**
* **Weak μ-opioid receptor agonist.** Parent drug = weak; **O-desmethyltramadol (M1)** (via **CYP2D6**) = much **stronger μ agonist** → main opioid effect.
* **Monoamine reuptake inhibition (SNRI):** inhibits **serotonin (5-HT)** and **noradrenaline** reuptake in the dorsal horn → descending inhibitory pain pathway activation.
**Other effects / receptors (minor):**
* Very weak **NMDA modulation** described; not clinically dominant.
**Clinical effects from the above:**
* **Analgesia** (moderate) with **opioid-sparing** properties.
* **Less respiratory depression** than pure μ-agonists at usual doses—but still possible (esp. ultrarapid CYP2D6 metabolisers or with other sedatives).
* **Seizure threshold lowered** (monoaminergic component).
* **Serotonergic effects** → risk of **serotonin syndrome** with SSRIs/SNRIs/MAOIs/linezolid/triptans.
* **Nausea, dizziness**, sweating; **less constipation** than morphine but still present.
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# 2) Vial strength, preparation & basic pharmacokinetics (+ disadvantages)
**Forms:**
* **IV/IM**: 50 mg/mL (1 mL amp).
* **PO**: 50 mg immediate-release (IR); 100/150/200 mg extended-release (ER).
**PK (adult):**
* **Onset:** PO 30–60 min (peak 2–3 h); IV 5–10 min.
* **Duration:** ~6 h (IR).
* **Metabolism:** hepatic **CYP2D6 → M1 (active)**; **CYP3A4/2B6** → N-desmethyl (inactive).
* **Elimination:** renal (parent + metabolites).
* **Half-life:** parent ~6 h; **M1 ~7–9 h** (prolonged in renal impairment).
**Disadvantages from PK/PD:**
* **High inter-patient variability** (CYP2D6 phenotype).
* **Seizure risk**, **serotonin toxicity** potential.
* Accumulates in **renal**/severe **hepatic** impairment → prolonged sedation, respiratory depression.
* **Not reliable** for severe acute pain; ceiling effect.
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# 3) Practical dosing
## A. Peri-operative / ward analgesia (adult)
* **PO IR:** **50–100 mg** q6h PRN (usual max **400 mg/day**).
* **PO ER:** **100 mg once daily**, titrate by 100 mg every 3–7 days to **200–300 mg/day** (follow local max).
* **IV:** **50–100 mg** slow IV over ≥2–3 min, q6h PRN (avoid rapid pushes).
* **Post-anaesthetic shivering (alternative to pethidine):** **0.5–1 mg/kg IV** slowly (common practice).
## B. ICU
* **Not a first-line ICU analgesic** (variable effect, interactions).
* Consider **enteral tramadol** for step-down analgesia when extubating or reducing strong opioids: **50–100 mg PO q6–8h** (reduce in renal/hepatic impairment).
* **Avoid continuous IV infusions.**
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# 4) Special populations — dosing cautions
### Pregnancy
* Short courses may be used if benefits outweigh risks. **Chronic use** near term → neonatal respiratory depression/withdrawal. Prefer alternatives where possible.
### Lactation
* **Avoid**: risk of neonatal sedation/apnoea—especially if mother is a **CYP2D6 ultrarapid metaboliser** (higher M1 in milk).
### Hepatic impairment
* **Reduce dose/extend interval.** Severe hepatic failure: **50 mg PO/IV q12h** (or avoid); ER not recommended.
### Renal impairment
* **CrCl <30 mL/min:** **50–100 mg q12h**; **max 200 mg/day**. Avoid ER formulations. Monitor for accumulation.
### Obesity
* Dose clinically (no clear TBW scaling benefit). Start low; titrate to effect (sedation risk with co-depressants).
### Paediatrics
* **Contraindicated <12 years.**
* **Avoid 12–18 years** after **tonsillectomy/adenoidectomy** or in **OSA/obesity** (ultrarapid CYP2D6 → life-threatening respiratory depression).
* If used where allowed: specialist dosing only, with close monitoring.
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# 5) Drug interactions (clinically key)
* **Serotonergic agents** (**SSRIs/SNRIs/TCAs/MAOIs/linezolid/methylene blue/triptans**): ↑ **serotonin syndrome** risk → agitation, clonus, hyperreflexia, hyperthermia; **avoid MAOIs within 14 days**.
* **CYP2D6 inhibitors** (fluoxetine, paroxetine, bupropion, quinidine, duloxetine): ↓ M1 formation → **less analgesia** but **more serotonergic AEs**.
* **CYP3A4 inhibitors/inducers** (azoles, macrolides, protease inhibitors, rifampicin, carbamazepine): alter tramadol levels → monitor/titrate.
* **Seizure threshold-lowering drugs** (bupropion, clozapine, tramadol itself, TCAs): additive **seizure risk**.
* **CNS depressants** (benzos, opioids, alcohol, propofol): additive sedation/respiratory depression.
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# 6) Significant complications & management
| Complication | Mechanism / Features | What to do |
| ------------------------------ | ---------------------------------------------------------------------------- | ---------------------------------------------------------------------------------------------------------------------- |
| **Serotonin syndrome** | SNRI effect + serotonergic co-meds | Stop serotonergic agents, supportive care, **benzodiazepines**, active cooling; **cyproheptadine** if moderate–severe. |
| **Seizures** | Lowers threshold; higher risk with high doses/renal failure/CYP interactions | Airway, **benzodiazepine** IV, correct electrolytes; avoid further tramadol. |
| **Respiratory depression** | μ-agonism (notable in ultrarapid CYP2D6, co-depressants) | Airway/ventilation; **naloxone** titration (small increments; risk of precipitating pain/sympathetic surge). |
| **Hypoglycaemia (rare)** | Proposed insulin modulation | Monitor glucose in unexplained diaphoresis/confusion. |
| **Hyponatraemia/SIADH (rare)** | Serotonergic effect | Check Na⁺ if confusion/seizure; fluid management per SIADH. |
| **Nausea, dizziness** | Central effects | Ondansetron/metoclopramide; slow position changes. |
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## Pocket viva line
*Tramadol provides **dual-mechanism** analgesia (weak **μ-agonist** + **SNRI**). It has **variable efficacy** (CYP2D6 dependent), **less respiratory depression** than strong opioids at modest doses, but carries **seizure** and **serotonin-syndrome** risks and **accumulates** in renal/hepatic impairment. Typical adult dosing: **50–100 mg PO/IV q6h** (max **400 mg/day**; reduce to **200 mg/day** if **CrCl <30**).*
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