CLONIDINE
Clinical safety rating: safe
Animal studies have demonstrated safety
Selective alpha-2 adrenergic agonist in the brainstem, activating inhibitory neurons, reducing sympathetic outflow, leading to decreased peripheral vascular resistance, renal vascular resistance, heart rate, and blood pressure.
| Metabolism | Primarily hepatic via CYP2D6, with 50% metabolized; 50% excreted unchanged in urine. |
| Excretion | Renal: 40-60% unchanged; hepatic metabolism accounts for ~50%, with metabolites excreted renally. Fecal excretion <5%. |
| Half-life | Terminal elimination half-life: 6-20 hours (mean 12 hours), prolonged in renal impairment (up to 40 hours). |
| Protein binding | 20-40% bound to plasma proteins (primarily albumin). |
| Volume of Distribution | 2.1-3.5 L/kg, indicating extensive tissue distribution; lower in neonates (1.6 L/kg). |
| Bioavailability | Oral: 75-95% (immediate-release), 60-89% (extended-release); Transdermal: 60-70% (absorption rate-limited). |
| Onset of Action | Oral: 30-60 minutes; Transdermal: 2-3 days delayed onset; IV: 5-10 minutes; Epidural: 15-30 minutes. |
| Duration of Action | Oral: 6-10 hours (immediate-release), 12-24 hours (extended-release); Transdermal: 7 days (per patch). |
Adults: Initial 0.1 mg orally twice daily; maintenance 0.2-0.6 mg/day in divided doses. Transdermal: 0.1-0.3 mg/day patch applied every 7 days. Epidural infusion: 30-40 mcg/hour.
| Dosage form | SYSTEM |
| Renal impairment | eGFR 10-50 mL/min: Reduce dose by 25-50%. eGFR <10 mL/min: Reduce dose by 50-75% or extend interval. Not removed by hemodialysis. |
| Liver impairment | Child-Pugh Class B: Reduce dose by 50%. Child-Pugh Class C: Avoid use or reduce dose by 75%. |
| Pediatric use | Oral: Initial 5-10 mcg/kg/day in 2-3 divided doses; maximum 25 mcg/kg/day. Transdermal: Not recommended for children <12 years. |
| Geriatric use | Start with lowest dose (0.05 mg twice daily) due to increased sensitivity, risk of bradycardia, and orthostatic hypotension. Monitor renal function. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
CNS depressants may enhance sedative effects Abrupt discontinuation can cause rebound hypertension and nervousness.
| Breastfeeding | Clonidine is excreted into breast milk. Milk-to-plasma ratio (M/P) is approximately 1.5-2.0. Relative infant dose ~2-3% of maternal weight-adjusted dose. Monitor infant for hypotension, bradycardia, drowsiness, and poor feeding. Use with caution; benefits should outweigh risks. |
| Teratogenic Risk | Clonidine is FDA Pregnancy Category C. Animal studies have shown fetal harm (increased resorptions, reduced fetal weight, skeletal variations). There are no adequate human studies. First trimester: risk cannot be ruled out; use only if benefit outweighs risk. Second/third trimester: may cause neonatal hypertension, bradycardia, or irritability with chronic use; avoid abrupt discontinuation near term to prevent maternal rebound hypertension. |
■ FDA Black Box Warning
No FDA black box warning.
| Common Effects | ADHD |
| Serious Effects |
["Hypersensitivity to clonidine or any component","Concurrent use with monoamine oxidase inhibitors (MAOIs) or within 14 days of MAOI use"]
| Precautions | ["Rebound hypertension (severe) upon abrupt discontinuation","CNS depression","Bradycardia and heart block","Syncope","Sedation/drowsiness","Dry mouth","Orthostatic hypotension","Renal impairment (dose adjustment)","Use in pregnancy (Category C)"] |
| Food/Dietary | No significant food interactions reported. However, alcohol may potentiate central nervous system depression and should be avoided or limited. |
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| Fetal Monitoring | Monitor maternal blood pressure and heart rate regularly. Fetal monitoring: assess fetal heart rate and growth via ultrasound if chronic use. In third trimester, consider neonatal monitoring for transient hypertension or bradycardia after delivery. |
| Fertility Effects | Clonidine may affect reproductive function. In males, it can reduce libido and cause erectile dysfunction. In females, it may disrupt ovulatory cycles due to central alpha-2 agonism affecting GnRH secretion. No specific data on infertility reversal. Impairment is generally reversible upon discontinuation. |
| Clinical Pearls | Clonidine may cause rebound hypertension upon abrupt discontinuation; taper over 2-4 days. Monitor for bradycardia and sedation, especially in elderly. Transdermal patch efficacy may be reduced in patients with thick dermis or high body temperature. Use with caution in patients with pre-existing bradycardia or sick sinus syndrome. Clonidine can mask symptoms of hypoglycemia. For hypertensive urgencies, oral loading dose 0.1-0.2 mg can be repeated hourly until response (max 0.7 mg). |
| Patient Advice | Do not stop taking clonidine suddenly; ask your doctor about a gradual dose reduction to avoid a dangerous rise in blood pressure. · If you use the transdermal patch, apply it to a hairless area on the upper arm or chest, and rotate sites to avoid skin irritation. · This medication may cause drowsiness or dizziness; avoid driving or operating machinery until you know how it affects you. · Avoid alcohol, as it may increase the sedative effects of clonidine. · Inform your doctor if you experience a slow heart rate, fainting, or severe constipation. · If you have diabetes, clonidine may hide the warning signs of low blood sugar; monitor blood glucose regularly. |