TAVIST
Clinical safety rating: caution
Comprehensive clinical and safety monograph for TAVIST (TAVIST).
Antihistamine; selective inverse agonist at histamine H1 receptors, blocking histamine-mediated allergic and inflammatory responses.
| Metabolism | Hepatic via CYP450 isoenzymes (primarily CYP3A4); extensive first-pass metabolism. |
| Excretion | Renal excretion of metabolites (approx. 60%) and unchanged drug (<5%); biliary/fecal elimination accounts for about 40%. |
| Half-life | Terminal elimination half-life is 12-15 hours in healthy adults; prolonged in renal/hepatic impairment. |
| Protein binding | Approximately 95% bound to plasma proteins (primarily albumin). |
| Volume of Distribution | Vd is about 2.5-4.0 L/kg, indicating extensive tissue distribution. |
| Bioavailability | Oral bioavailability is approximately 50-60% due to first-pass metabolism. |
| Onset of Action | Oral: 30-60 minutes; peak effect at 2-4 hours. |
| Duration of Action | Duration of antihistamine effect is 4-6 hours for oral administration; may be longer (up to 12 hours) in some individuals. |
| Molecular Weight | 310.8 |
1.34 mg orally twice daily; maximum 8.04 mg/day.
| Dosage form | TABLET |
| Renal impairment | CrCl <10 mL/min: contraindicated. CrCl 10-50 mL/min: reduce dose by 50% to 1.34 mg once daily. |
| Liver impairment | Child-Pugh class B or C: reduce dose by 50% to 1.34 mg once daily. Class A: no adjustment. |
| Pediatric use | Not recommended for children under 12 years. For ages 12-17: same as adult dosing. |
| Geriatric use | Initiate at 1.34 mg once daily due to increased anticholinergic sensitivity and risk of confusion, falls. |
| 1st trimester | Crosses placenta; animal studies show risk, but human data limited. Avoid unless benefit outweighs risk. |
| 2nd trimester | Crosses placenta; use only if clearly needed. Anticholinergic effects may affect fetal heart rate. |
| 3rd trimester | Crosses placenta; may cause uterine irritability or premature labor. Avoid near term. |
Clinical note
Comprehensive clinical and safety monograph for TAVIST (TAVIST).
| Placental transfer | Crosses placenta; extent not quantified but documented in animal and human studies. |
| Breastfeeding | Excreted into breast milk in low amounts; may cause drowsiness or irritability in infant. Use caution, especially in neonates or preterm infants. |
| Lactation Rating |
■ FDA Black Box Warning
None
| Serious Effects |
Hypersensitivity to clemastine or other antihistaminesMAOI therapy (concurrent or within 14 days)Narrow-angle glaucomaSymptomatic prostatic hypertrophyBladder neck obstructionStenosing peptic ulcerPyloroduodenal obstructionNewborn or premature infantsLactation (relative)
| Precautions | Drowsiness and sedation may impair ability to drive or operate machinery, Avoid concurrent use with CNS depressants (e.g., alcohol, benzodiazepines), Caution in patients with increased intraocular pressure, hyperthyroidism, cardiovascular disease, or hypertension, Use with caution in elderly patients due to increased sensitivity to anticholinergic effects |
| Food/Dietary | Avoid alcohol and grapefruit juice. Food may slightly delay absorption but does not affect overall bioavailability. No significant food interactions reported. |
Loading safety data…
| L3 - Probably Compatible (moderate risk) |
| Teratogenic Risk | Pregnancy Category C. In first trimester, case reports suggest possible association with fetal malformations (cleft palate, inguinal hernia), although animal studies show no teratogenicity at doses up 125 mg/kg/day. Second and third trimesters: No known specific risks; antihistamines may cause uterine contractions near term. |
| Fetal Monitoring | Monitor maternal blood pressure and heart rate; observe for sedation. Fetal monitoring if used late pregnancy due to potential oxytocin-like effects. Assess neonatal CNS and respiratory status after delivery if used near term. |
| Fertility Effects | No significant impact on fertility reported in animal studies. In humans, antihistamines like clemastine (active ingredient) have not been linked to impaired fertility. |
| Clinical Pearls | Tavist (clemastine fumarate) is a first-generation antihistamine with significant anticholinergic properties; use cautiously in elderly due to risk of confusion, urinary retention, and falls. It causes marked sedation, so avoid concurrent CNS depressants. Onset is 30-60 minutes, duration 12-24 hours. Not recommended for children under 6 years due to paradoxical excitation risk. |
| Patient Advice | Take exactly as prescribed; do not exceed recommended dose. · May cause drowsiness; avoid driving or operating machinery until you know how it affects you. · Avoid alcohol and other sedatives while taking this medication. · Use caution in hot weather as it may decrease sweating and increase risk of heat stroke. · If you miss a dose, skip it; do not double the next dose. · Report any signs of allergic reaction, confusion, or difficulty urinating to your doctor. |