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GABAPENTIN (NEURONTIN) AND PREGABALIN (LYPRALIN, LYRICA)

Description

Gabapentin and pregabalin are termed gabapentinoids and are used orally. They are useful for treating epilepsy, neuropathic pain (such as postherpetic neuralgia), alcohol withdrawal and for reducing postoperative pain when given preoperatively. These drugs act by affecting pre-synaptic voltage-gated calcium channels. They also increase the synthesis of GABBA. There is a limitation on gabapentin's oral bioavailability due to saturation of absorption pathways. Pregabalin oral absorption is not limited.

Dose

Adult

Neuropathic pain—gabapentin 300 mg PO q 8 h to a maximum of 3600 mg/day. Pregabalin 75 mg q 12 h, increase to 150 mg q 12 h after 3—7 days, to a maximum of 300 mg q 12 h.

Postoperative pain—preoperative gabapentin 600–1200 mg PO may significantly reduce postoperative pain and PCA use.1

Advantages

  1. Gabapentin and morphine have synergistic analgesic effects.2

  2. Eliminated unchanged in urine but is removed by haemodialysis.

  3. Extremely safe without serious toxicity, even after massive overdose.

Disadvantages

  1. May cause somnolence, dizziness, ataxia and fatigue.

  2. Use with caution in patients with renal impairment.

  3. May cause acute reversible kidney transplant dysfunction.3

  4. Can cause convulsions (although rarely).

  5. Not recommended for use while breast feeding as it is excreted in breast milk and the effects on the neonate are unknown.

  6. Gabapentinoids my cause depression, aggressive behaviour and suicidal ideation.

GAS EMBOLISM

Description

The term ‘gas embolism’ describes gas entering a vein or artery or gas forming in the blood stream. This can cause many adverse effects and/or death.

Causes of venous gas embolism

  1. Exposure of cut veins or venous sinuses to air when a pressure gradient favours the entry of air into the vein. This is particularly likely with neurosurgery and liver surgery.

  2. Gas entry into the vein through IV access devices—cannula, central line (including removal of a central line).

  3. Operations and procedures involving gas insufflation e.g. laparoscopy, colonoscopy.

  4. Trauma.

  5. Pulmonary barotrauma.

  6. Decompression sickness.

  7. Exposure to vacuum.

Causes of arterial gas embolism

  1. Paradoxical embolism—venous gas enters the arterial system via the lungs, patent foramen ovale or a heart defect such as ventricular septal defect (VSD).

  2. Decompression sickness.

  3. Trauma.

  4. Pulmonary barotrauma.

  5. Accidental injection of air into an artery during procedures such as a cervical plexus block.

  6. Exposure to vacuum.

Pathophysiology of venous and arterial gas embolism

  1. Arterial gas embolism causes obstruction of small vessels, causing ischaemia of the tissue beyond the bubble(s).

  2. Venous air embolus causes obstruction of flow from the heart and through the pulmonary vasculature.

  3. Venous air also causes an endothelial inflammatory response, which can lead ...

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