Is buclizine (antihistamine) suitable for an 18-year-old?

Buclizine Use in an 18-Year-Old

Buclizine is suitable for an 18-year-old, as 18 years is considered the adult threshold for medication use, and buclizine is a first-generation antihistamine approved for adults. 1, 2

Understanding Buclizine

Buclizine is a piperazine-derivative first-generation antihistamine with sedating, antimuscarinic, and moderate sedative properties, primarily used for its antiemetic effect in preventing motion sickness and migraine. 2

Age Appropriateness

• At 18 years of age, patients are considered adults for medication prescribing purposes, as FDA-approved labeling indicates this threshold for adult dosing. 1
• No specific age restrictions exist for buclizine use in adults, though pediatric safety data are limited. 3

Clinical Efficacy Considerations

Motion Sickness Prevention

• First-generation antihistamines (the class to which buclizine belongs) are probably effective at preventing motion sickness symptoms under natural conditions, with approximately 40% symptom prevention compared to 25% with placebo (RR 1.81,95% CI 1.23 to 2.66). 3
• The evidence for motion sickness treatment is moderate-certainty under natural conditions but very low-certainty under experimental conditions. 3

Mechanism of Action

• Antihistamines like buclizine may work primarily on a central level rather than through sensory-specific mechanisms, particularly affecting motion-sickness evoked by everyday activities. 4

Important Safety Warnings for Young Adults

Sedation Risk

• First-generation antihistamines like buclizine cause significantly more sedation than placebo (66% vs 44%; RR 1.51,95% CI 1.12 to 2.02). 3
• Sedating effects persist longer than plasma levels, causing next-day impairment even when taken at bedtime. 5
• Performance impairment can occur without subjective awareness of drowsiness. 5

Fall Risk

• Even in younger adults aged 18-64 years, antihistamines with anticholinergic properties are associated with increased fall risk (hazard ratio 2.94,95% CI 2.81-3.08). 6
• This risk applies to vestibular suppressants used for dizziness and may extend to other indications. 6

Anticholinergic Effects

• Buclizine has antimuscarinic properties that can cause dry mouth, dry eyes, constipation, and urinary retention. 2, 5
• These anticholinergic effects may worsen conditions in patients with intoxication from drugs with anticholinergic properties. 7

Cognitive Impairment

• First-generation antihistamines may result in impaired cognition (29% vs 33% placebo), though this difference was not statistically significant. 3
• Blurred vision occurs in approximately 14% of users versus 12.5% with placebo. 3

Safer Alternatives to Consider

Second-generation antihistamines are strongly preferred when chronic antihistamine therapy is needed, as they cause less sedation and fewer anticholinergic effects. 5

• Fexofenadine, loratadine, and desloratadine at recommended doses do not cause sedation and are safer options for young adults requiring antihistamine therapy. 5
• These alternatives should be considered first, reserving buclizine for situations where sedation is specifically desired or when second-generation agents have failed. 5

Special Populations

Renal Impairment

• In moderate renal impairment (creatinine clearance 10-20 mL/min), doses of sedating antihistamines should be halved. 7, 5
• Sedating antihistamines should be avoided in severe renal impairment (creatinine clearance <10 mL/min). 7

Hepatic Impairment

• Sedating antihistamines should be avoided in severe liver disease due to inappropriate sedating effects and risk of precipitating hepatic coma. 7, 5

Clinical Algorithm for Antihistamine Selection in 18-Year-Olds

1. Determine if an antihistamine is truly necessary for the specific indication (motion sickness, nausea, allergic symptoms). 5

2. If antihistamine therapy is indicated, first select a second-generation agent (fexofenadine, loratadine, or desloratadine) unless sedation is specifically desired. 5

3. Consider buclizine only if:

   • Sedation is therapeutically beneficial 5
   • Second-generation antihistamines have failed 5
   • Short-term use for acute motion sickness prevention is needed 3, 2

4. Counsel the patient about:

   • Increased sedation and next-day impairment risk 3, 5
   • Fall risk, even in young adults 6
   • Avoiding driving or operating machinery 5
   • Anticholinergic side effects 2, 5

5. Monitor for adverse effects including excessive sedation, falls, confusion, dry mouth, constipation, urinary retention, and blurred vision. 5, 3

Common Pitfalls to Avoid

• Do not assume young age eliminates fall risk with sedating antihistamines—the hazard ratio for falls remains elevated (2.94) even in adults aged 18-64 years. 6
• Do not use buclizine as routine first-line therapy when non-sedating alternatives are available and appropriate. 5
• Do not underestimate next-day impairment even when the medication is taken at bedtime. 5
• Avoid combining buclizine with other CNS depressants including benzodiazepines, alcohol, or other sedating medications without careful consideration. 7