Acetazolamide tablets for altitude travel
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Here is a thorough guide to acetazolamide (Diamox) for altitude travel, drawing from Harrison's Principles of Internal Medicine (2025), Goldman-Cecil Medicine, Rosen's Emergency Medicine, and a 2025 network meta-analysis:
Acetazolamide (Diamox) for Altitude Travel
What It Is and How It Works
Acetazolamide is a carbonic anhydrase inhibitor. At altitude, it causes a bicarbonate diuresis, which creates a mild metabolic acidosis. The body compensates by increasing ventilation - mimicking the acclimatisation response. This raises arterial oxygen saturation, particularly during sleep when ventilation naturally drops and hypoxia worsens. It does not mask symptoms the way dexamethasone does; it actually promotes acclimatisation.
Who Should Take It
The decision depends on risk stratification:
- Low risk (slow ascent, no prior AMS history) - prophylaxis generally not needed
- Moderate/high risk - prophylaxis recommended:
- Prior history of acute mountain sickness (AMS), HACE, or HAPE
- Rapid or unavoidable ascent (e.g. flying into Lhasa at 3658 m, Cusco at 3400 m)
- Ascent to sleeping altitude >3000 m without adequate acclimatisation time
- Dispatch of rescue personnel to altitude
Dosing
| Use | Adult Dose | Paediatric Dose |
|---|---|---|
| Prophylaxis (AMS/HACE prevention) | 125 mg orally twice daily | 2.5 mg/kg/dose (max 125 mg) twice daily |
| Treatment of established AMS | 250 mg orally twice daily | 2.5 mg/kg/dose twice daily |
When to start: Begin 24-48 hours before ascent
When to stop: Continue for the first 2 days at your target altitude (or until fully acclimatised)
The lower 125 mg prophylactic dose is equally effective as 250 mg with fewer side effects, per Rosen's Emergency Medicine. Harrison's 2025 confirms 125 mg q12h for prevention and 250 mg q12h for treatment.
Ascent Rate Guidelines (non-pharmacological, key context)
- Above 3000 m: limit sleeping altitude gain to ≤300 m/day from the previous night
- Take an extra rest day for every 3 days of altitude gain
- "Climb high, sleep low" - day excursions to higher altitude followed by descent to sleep
- First overnight sleeping altitude should ideally not exceed 2800 m (9200 ft)
Side Effects
Common (often unavoidable at therapeutic doses):
- Paraesthesias (tingling in hands, feet, lips) - very common
- Increased urination (diuretic effect)
- Altered taste of carbonated drinks (CO2 seems flat)
- Fatigue, nausea
Rare but serious:
- Aplastic anaemia (very rare)
- Stevens-Johnson syndrome (very rare)
Contraindications and Cautions
- Sulfa anaphylaxis: absolute contraindication - use dexamethasone (4 mg q12h) instead. Note: allergy to sulfonamide antibiotics is NOT automatically a contraindication; only prior anaphylaxis to sulfa drugs warrants avoidance.
- Pregnancy: generally avoided (teratogenic in animal studies)
- Severe renal impairment or hepatic failure
- Electrolyte imbalances (hyponatraemia, hypokalaemia)
- Concurrent use with high-dose aspirin (toxicity risk)
Alternatives if Acetazolamide Is Contraindicated
| Drug | Indication | Dose |
|---|---|---|
| Dexamethasone | AMS/HACE prevention and treatment | 4 mg q12h (prevention); 4 mg q6h (treatment) |
| Nifedipine SR | HAPE prevention/treatment | 30 mg SR q12h |
| Tadalafil | HAPE prevention | 10 mg twice daily |
| Ibuprofen | AMS headache prevention (comparable to acetazolamide for headache alone) | 400-600 mg three times daily |
When to Descend Regardless of Medication
Acetazolamide does not eliminate the need to descend. Immediate descent (plus oxygen, dexamethasone for HACE or nifedipine for HAPE) is mandatory for:
- HACE: ataxia, confusion, altered consciousness
- HAPE: breathlessness at rest, persistent cough, frothy/pink sputum, very low O2 saturation
- Any rapidly worsening symptoms
Recent Evidence
A 2025 network meta-analysis (PMID 40383249, Travel Medicine and Infectious Diseases) comparing pharmacological interventions for AMS prevention confirms acetazolamide remains the best-evidenced first-line prophylactic agent. A January 2026 WADA guideline also affirms it as "the only medication with well-established efficacy in facilitating acclimatisation."
Note: Acetazolamide is prohibited in-competition under WADA rules (it can mask diuretic use). Travellers who are competitive athletes need a Therapeutic Use Exemption (TUE).
Sources: Harrison's Principles of Internal Medicine 22e (2025); Goldman-Cecil Medicine; Rosen's Emergency Medicine; Goodman & Gilman's Pharmacological Basis of Therapeutics; WADA TUE Guideline Jan 2026; PMID 40383249.
Trigeminal neuralgia
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Trigeminal Neuralgia
Definition
Trigeminal neuralgia (TN) is a paroxysmal, excruciatingly painful condition involving one or more divisions of the trigeminal nerve (CN V). It is widely regarded as one of the most severe pain syndromes known in medicine.
Classification (ICHD-3)
| Type | Description |
|---|---|
| Classical TN | Vascular compression of the trigeminal nerve root, with MRI/surgical evidence of nerve atrophy or displacement |
| Secondary TN | Caused by an underlying disease (multiple sclerosis, tumour, vascular malformation) |
| Idiopathic TN | No causative lesion found and no clear morphological change at the nerve root |
Epidemiology
- Incidence: ~4 per 100,000 people
- Onset after age 40 in 90% of cases; incidence rises with age
- Slight female predominance (1.5:1 female:male)
- In younger patients, multiple sclerosis is an important associated cause
- Rare familial cases suggest a genetic contribution in some families
Pathophysiology
The most accepted mechanism involves neurovascular compression of the trigeminal nerve at the root entry zone near the pons - most commonly by the superior cerebellar artery, but also by the anterior/posterior inferior cerebellar arteries or the superior petrosal vein. Chronic pulsatile compression causes focal demyelination of primary trigeminal afferents. This demyelination produces focal hyperexcitability, leading to ectopic and repetitive neuronal discharges triggered by normally innocuous stimuli (ephaptic transmission).
In secondary TN (e.g. MS plaques in the pons), the same mechanism - demyelination at the root entry zone - is the likely pathway.
Clinical Features
Pain characteristics:
- Quality: Electric shock-like, shooting, lancinating, stabbing
- Duration: Each attack lasts seconds (up to 2 minutes); attacks can fire repeatedly and blur together
- Distribution: Almost always unilateral; V2 (cheek, upper lip, upper teeth) and V3 (chin, lower teeth, lower lip) are most commonly affected; V1 (around the eye) alone is very rare
- After many attacks within a few hours, a residual dull aching may persist between volleys
Trigger factors (stimuli that provoke attacks):
- Touching the face or nasolabial fold (trigger zone may be remote from pain site)
- Chewing, talking, teeth brushing
- Cool breeze on the face
- Swallowing, smiling
Inter-attack period: Most patients are pain-free between attacks
Associated features:
- No sensory loss or motor deficit in classical TN (their presence suggests secondary TN or trigeminal neuropathy)
- Attacks during sleep are uncommon but do occur
- Frequent attacks can cause weight loss, dehydration, and depression
- 3-fold higher risk of anxiety and depression compared to controls; ~30% develop PTSD symptoms from fear of attacks
Diagnosis
Diagnosis is primarily clinical, based on ICHD-3 criteria:
- Paroxysmal attacks of pain lasting from a fraction of a second up to 2 minutes
- Pain in the distribution of one or more trigeminal divisions
- Pain has at least one of: intense, sharp/shooting/stabbing quality OR triggered by innocuous stimuli
- Stereotyped, recurrent attacks
Investigations:
- MRI brain (mandatory for all new cases): to exclude secondary causes - MS plaques, posterior fossa tumours (meningioma, schwannoma), pontine lacunar infarcts, skull base malignancy, and vascular loops
- High-resolution MRI/MRA can identify neurovascular contact in some cases
- EMG and blink reflex studies: normal in classical TN
- Sensory loss, masticatory weakness, or other neurological signs = investigate for secondary cause
Differential diagnosis: Trigeminal autonomic cephalalgias (have autonomic features), atypical facial pain, idiopathic stabbing headache, Tolosa-Hunt syndrome, dental pathology (frequently misdiagnosed as dental pain - studies show up to 42% saw a dental specialist first)
Treatment
Medical (first-line)
| Drug | Class | Dose | Notes |
|---|---|---|---|
| Carbamazepine | Na-channel blocker | 600-1200 mg/day divided | First-line; ~70-90% response rate; start low (50-100 mg) and titrate slowly |
| Oxcarbazepine | Na-channel blocker | 300-1800 mg/day | Often better tolerated than CBZ; watch for hyponatraemia |
| Gabapentin | Gabapentinoid | 900-1800 mg/day | 2nd line; benign side-effect profile |
| Pregabalin | Gabapentinoid | As per neuropathic pain dosing | 2nd line |
| Baclofen | GABA-B agonist | 50-60 mg/day | 2nd line; useful add-on |
| Lamotrigine | Na-channel blocker | 100-400 mg/day | 2nd line; slow titration needed |
| Phenytoin | Na-channel blocker | 200-300 mg/day | 2nd/3rd line |
| Valproate | Multiple mechanisms | 500-1500 mg/day | 3rd line |
| Clonazepam | Benzodiazepine | 2-6 mg/day | 3rd line |
| Topiramate | Multiple | 50-200 mg/day | 3rd line |
| Botulinum toxin A | Neuromodulator | Injected into trigger zones | Emerging evidence; 2024 meta-analysis (PMID 38385501) confirms efficacy and safety |
Monitoring for carbamazepine/oxcarbazepine: Full blood count (agranulocytosis), liver function tests, and serum sodium at baseline, then in the first few months, then annually. Check HLA-B*1502 in patients of Han Chinese/Asian descent before starting carbamazepine (Stevens-Johnson risk).
Acute severe attack: IV fosphenytoin 15-20 mg PE/kg; topical ophthalmic anaesthetic (proparacaine) to the ipsilateral conjunctival sac can also abort attacks for hours to days.
Once pain is fully controlled, attempt dose tapering every few weeks to determine if remission has occurred.
Surgical (for refractory cases)
| Procedure | Mechanism | Best For | Key Points |
|---|---|---|---|
| Microvascular decompression (MVD) | Separates offending vessel from nerve; Teflon padding placed | Younger, fit patients | Posterior fossa craniotomy; 70% excellent pain relief at 10 years (Jannetta); preserves sensation; addresses the cause directly; mortality ~1%; CN IV/VII/VIII risk |
| Percutaneous radiofrequency thermocoagulation | Heat ablation of Gasserian ganglion | Elderly/medically unfit | Effective; risk of corneal anaesthesia (V1 lesion), dyaesthesia, anesthesia dolorosa |
| Percutaneous glycerol rhizolysis | Chemical nerve destruction | Elderly/medically unfit | Simpler than RF; higher recurrence |
| Percutaneous balloon compression | Mechanical ganglion compression | Elderly/medically unfit | Higher early recurrence (~2-3 years) |
| Gamma Knife stereotactic radiosurgery | Focused radiation to root entry zone | Patients unsuitable for open surgery | Less invasive; relatively high recurrence; risk of dysaesthesia in previously operated patients |
| Peripheral alcohol block | Nerve branch chemical ablation | Short-term/bridge | Relief in high proportion; relapse within 6-18 months in most; repeatable 1-2 times |
Patient selection principles (Bradley & Daroff):
- Young patient, medically fit, refractory to medications → MVD preferred
- Elderly or significant comorbidities → percutaneous ganglion procedures (RF thermocoagulation or balloon compression)
- Decisions must be individualised; no single surgical recommendation suits all patients
Course and Prognosis
- TN follows a relapsing-remitting pattern in many patients; spontaneous remissions can occur for months to years
- Over time, remissions may become shorter and attacks more refractory to medication
- Secondary TN (especially MS-related) tends to be more treatment-resistant
- With MVD, ~70% maintain excellent long-term pain control at 10 years
- TN significantly impairs quality of life; psychiatric comorbidity (anxiety, depression, PTSD) must be addressed
Recent Evidence
- A 2024 systematic review and meta-analysis (PMID 38385501, Clinical Journal of Pain) confirms botulinum toxin type A is effective and safe for TN, supporting its role as an option when standard medications fail or are not tolerated
- The European Academy of Neurology and Royal College of Surgeons of England have issued TN guidelines emphasising a multidisciplinary approach and recommending MRI for all patients at diagnosis
Sources: Bradley and Daroff's Neurology in Clinical Practice; Goldman-Cecil Medicine 2-Vol Set; Rosen's Emergency Medicine; Neuroanatomy through Clinical Cases 3e; Kaplan & Sadock's Comprehensive Textbook of Psychiatry; Harrison's Principles of Internal Medicine 22e (2025). Evidence update: PMID 38385501.
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