PYRILAMINE MALEATE
Clinical safety rating: caution
Comprehensive clinical and safety monograph for PYRILAMINE MALEATE (PYRILAMINE MALEATE).
Pyrilamine is a first-generation antihistamine that competitively antagonizes histamine at H1 receptors, thereby preventing histamine-mediated effects such as increased vascular permeability, vasodilation, and bronchoconstriction.
| Metabolism | Hepatic metabolism primarily via CYP450 enzymes, including CYP2D6 and CYP3A4. |
| Excretion | Primarily renal as metabolites; about 80-90% excreted in urine within 24 hours, with less than 5% unchanged; minor biliary/fecal elimination. |
| Half-life | Approximately 16-23 hours in healthy adults; may be prolonged in elderly or hepatic impairment. |
| Protein binding | Approximately 98-99% bound to serum proteins, primarily albumin. |
| Volume of Distribution | Approximately 5-10 L/kg; indicates extensive tissue distribution. |
| Bioavailability | Oral: approximately 70-90% due to first-pass metabolism; parenteral: 100%. |
| Onset of Action | Oral: 30-60 minutes; parenteral: 10-20 minutes. |
| Duration of Action | Oral: 4-6 hours; parenteral: 3-4 hours; clinical effects may last longer due to active metabolites. |
25-50 mg orally every 6-8 hours as needed, not to exceed 200 mg per day.
| Dosage form | TABLET |
| Renal impairment | eGFR 30-50 mL/min: administer every 12 hours; eGFR 15-29 mL/min: administer every 12-18 hours; eGFR <15 mL/min: administer every 24 hours or avoid use. |
| Liver impairment | Child-Pugh Class A: no adjustment needed; Child-Pugh Class B: reduce dose by 50%; Child-Pugh Class C: avoid use. |
| Pediatric use | Children 2-6 years: 6.25 mg (1/4 of 25 mg tablet) orally every 6 hours as needed; Children 6-12 years: 12.5 mg (1/2 of 25 mg tablet) orally every 6 hours as needed; maximum 75 mg per day for ages 6-12. |
| Geriatric use | Initiate at 12.5 mg orally every 12 hours; increase slowly as tolerated due to increased risk of sedation, confusion, and anticholinergic effects. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for PYRILAMINE MALEATE (PYRILAMINE MALEATE).
| Breastfeeding | Pyridoxine is excreted into breast milk; M/P ratio unknown. Use caution due to anticholinergic effects in infant; consider alternative antihistamines. |
| Teratogenic Risk | First trimester: No adequate human studies; animal studies not reported. Potential anticholinergic effects. Second and third trimesters: Limited data; theoretical risk of neonatal anticholinergic syndrome if used near term. Avoid use in pregnancy unless benefit outweighs risk. |
| Fetal Monitoring |
■ FDA Black Box Warning
None.
| Serious Effects |
["Hypersensitivity to pyrilamine or any component of the formulation","Newborns or premature infants","Lactation (excreted in breast milk)","Concurrent use with monoamine oxidase inhibitors (MAOIs)"]
| Precautions | ["CNS depressant effects: May cause drowsiness and impair mental/physical abilities; avoid concurrent use with alcohol or other CNS depressants.","Anticholinergic effects: Caution in patients with asthma, increased intraocular pressure, hyperthyroidism, cardiovascular disease, or urinary retention.","Use in elderly: Increased risk of dizziness, sedation, and confusion."] |
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| Monitor maternal heart rate, blood pressure, and urinary retention; fetal heart rate monitoring if used near term. |
| Fertility Effects | No specific studies on human fertility; anticholinergic effects may theoretically affect cervical mucus or sperm transport. |