Injections for Giddiness (Vertigo)

1. Symptomatic Injections (Acute Vertigo Attack)

Ondansetron (IV) - First Line

• Dose: 4 mg IV
• A 5-HT3 serotonin receptor antagonist; used as the first-line IV agent for symptomatic vertigo in the emergency setting
• A randomized trial comparing IM promethazine vs IV ondansetron in acute peripheral vertigo showed excellent improvement in both groups, with fewer side effects with ondansetron
• • Rosen's Emergency Medicine, p. 3856

Promethazine (IM) - Highly Effective but Caution Needed

• Dose: 12.5-25 mg IM; also available as 25 mg suppository
• Likely the most effective parenteral vestibular suppressant, but the FDA has issued a boxed warning against IV use (risk of tissue necrosis); IM or oral routes are preferred
• Useful when vomiting prevents oral intake
• • Rosen's Emergency Medicine, p. 3854-3856

Prochlorperazine (IV/IM) - Dopamine Antagonist

• Dose: 5-10 mg IV or IM (Stemetil®)
• A phenothiazine dopamine antagonist that blocks the chemoreceptor trigger zone and vomiting centre, which receives afferent input from the vestibular apparatus
• Available as injection, tablets, suppositories, and buccal preparation (Buccastem®) - the non-oral forms are particularly useful since vomiting patients cannot absorb oral doses
• Notable side effects: extra-pyramidal effects (more pronounced than other phenothiazines), less sedating
• Do NOT use in dizziness caused by orthostatic hypotension
• • Scott-Brown's Otorhinolaryngology, p. 4545-4565

Diazepam (IV) - Benzodiazepine

• Dose: 5 mg IV
• Useful in prolonged, severe vertigo episodes; patients prefer lying still in a dark quiet room and this agent helps
• Benzodiazepines (e.g., lorazepam 1-2 mg IV) can be given when vertigo is intractable and unresponsive to antiemetics
• Caution: Not recommended for discharge prescriptions in vestibular neuritis/labyrinthitis as benzodiazepines interfere with vestibular habituation/compensation
• • Goldman-Cecil Medicine, p. 3564; Rosen's Emergency Medicine, p. 3856

Cyclizine (IM) - Antihistamine

• Dose: 50 mg three times a day, may be given parenterally
• H1-receptor antagonist; acts mainly on the vomiting centre
• Less sedating than promethazine
• • Scott-Brown's Otorhinolaryngology, p. 4581-4583

2. Specific / Disease-Modifying Injections

Intratympanic Gentamicin - Meniere's Disease

• Injected through the tympanic membrane (or via grommet/round window catheter) directly into the middle ear
• Exploits gentamicin's vestibulotoxic effect - destroys vestibular hair cell function ("chemical/partial labyrinthectomy")
• Highly effective for controlling recurrent vertigo attacks in refractory unilateral Meniere's disease
• Risk: Hearing loss (varies with dose and frequency)
• • Scott-Brown's Otorhinolaryngology, p. 4588-4595

Intratympanic Methylprednisolone / Dexamethasone - Meniere's Disease

• Injected intratympanically for refractory vertigo in Meniere's disease
• Intratympanic methylprednisolone is comparable to intratympanic gentamicin in reducing vertiginous attacks but preserves hearing - preferred when residual hearing needs to be protected
• Intratympanic dexamethasone achieved substantial vertigo control in ~61% of patients in one series
• • Goldman-Cecil Medicine, p. 3562; Scott-Brown's Vol 2, p. 6326

Methylprednisolone (systemic IV/IM) - Vestibular Neuritis

• Dose: 1 mg/kg/day for 5 days, then tapered over 15 days
• Effective (at least short-term) for vestibular neuritis; antiviral agents have NOT been shown to add benefit
• • Goldman-Cecil Medicine, p. 3562

3. Summary Table

Key Clinical Points

• Acute attacks: Start with IV ondansetron 4 mg; use IM promethazine if needed (avoid IV route)
• Intractable vertigo unresponsive to antiemetics: Add IV lorazepam 1-2 mg
• Vestibular neuritis: Systemic corticosteroids (methylprednisolone); avoid prolonged benzodiazepines
• Refractory Meniere's with good hearing: Intratympanic steroids preferred over gentamicin
• Refractory Meniere's, hearing already lost: Intratympanic gentamicin for definitive vestibular ablation
• Do not use prochlorperazine or chlorpromazine if dizziness is from orthostatic hypotension