NATPARA
Clinical safety rating: caution
Comprehensive clinical and safety monograph for NATPARA (NATPARA).
Recombinant human parathyroid hormone (PTH 1-84) that binds to PTH1 receptors, increasing serum calcium by enhancing renal calcium reabsorption, intestinal calcium absorption, and bone resorption.
| Metabolism | Metabolized in the liver via proteolytic cleavage, primarily by cathepsin D and other proteases. |
| Excretion | Primarily renal (≥95% as intact parathyroid hormone and metabolites); biliary/fecal elimination minimal (<5%) |
| Half-life | Terminal half-life approximately 2–5 minutes (subcutaneous); rapid clearance with clinical context: requires twice-daily dosing due to short half-life |
| Protein binding | Approximately 55–60% bound to plasma proteins, primarily albumin |
| Volume of Distribution | Approximately 0.1–0.2 L/kg; reflects limited extravascular distribution, primarily in plasma and interstitial space |
| Bioavailability | Subcutaneous: approximately 55% (relative to intravenous injection) |
| Onset of Action | Subcutaneous: serum calcium elevation begins within 15–30 minutes |
| Duration of Action | Subcutaneous: up to 6–8 hours; clinical note: serum calcium peaks at 2–4 hours post-dose, declines to baseline by 8 hours |
| Molecular Weight | 4117.8 |
Initial dose: 50 mcg subcutaneously once daily, titrate in 25 mcg increments every 2-4 weeks based on serum calcium and symptoms, maintenance dose range: 25-100 mcg once daily.
| Dosage form | INJECTABLE |
| Renal impairment | eGFR <30 mL/min/1.73 m2: initiate at 25 mcg daily, titrate cautiously; eGFR 30-59: no specific adjustment but monitor calcium; eGFR ≥60: no adjustment. |
| Liver impairment | No formal studies; use with caution in severe hepatic impairment (Child-Pugh C) with increased monitoring. |
| Pediatric use | Not approved for patients <18 years; safety and efficacy not established. |
| Geriatric use | No specific dose adjustment; consider age-related renal decline and lower starting dose (25 mcg). |
| 1st trimester | No adequate human data; animal studies not available for this formulation; theoretical risk based on PTH activity; avoid unless clearly needed. |
| 2nd trimester | No adequate human data; potential for altered calcium homeostasis during pregnancy; use only if benefit outweighs risk. |
| 3rd trimester | No adequate human data; may affect maternal calcium levels and fetal bone development; monitor serum calcium closely if used. |
Clinical note
Comprehensive clinical and safety monograph for NATPARA (NATPARA).
| Placental transfer | Parathyroid hormone (PTH) is known to cross the placenta; specific data for NATPARA are lacking. |
| Breastfeeding | Excretion into human milk is unknown; because many drugs are excreted in milk and potential for serious adverse reactions in breastfeeding infants, a decision should be made whether to discontinue nursing or discontinue the drug. |
■ FDA Black Box Warning
None.
| Serious Effects |
Hypersensitivity to parathyroid hormone or any excipientPaget's disease of boneUnexplained elevation of alkaline phosphatasePrior external beam or implant radiation therapy involving the skeletonBone metastases or malignant bone tumorsPre-existing hypercalcemiaMetabolic bone diseases other than osteoporosis
| Precautions | Risk of osteosarcoma (increased with duration of use; avoid in patients with increased baseline risk), Digitalis toxicity, Hypocalcemia exacerbation upon discontinuation, Hypercalcemia and hypercalciuria requiring monitoring, Hypomagnesemia, Hypotension with rapid IV administration (not approved IV), Laboratory test interference (unlikely) |
| Food/Dietary | Avoid excessive dietary calcium intake beyond prescribed supplements as it may increase risk of hypercalcemia. High-oxalate foods (e.g., spinach, rhubarb, beets) may reduce calcium absorption; separate intake from calcium supplements by at least 2 hours. Foods high in phosphorus (e.g., dairy, nuts, whole grains) may affect calcium balance; maintain consistent intake. Do not consume high-dose vitamin D or vitamin A without medical supervision. |
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| Lactation Rating | L3 (Moderately Safe) |
| Teratogenic Risk | NATPARA (parathyroid hormone) is classified as Pregnancy Category C. In animal studies, parathyroid hormone has been associated with reduced fetal weight and skeletal abnormalities when administered during organogenesis. There are no adequate and well-controlled studies in pregnant women. The risk is likely highest during the first trimester due to skeletal development. Exposure in the second and third trimesters may affect fetal calcium homeostasis, but specific human data are lacking. Use only if potential benefit justifies potential risk to the fetus. |
| Fetal Monitoring | Monitor serum calcium, phosphate, and parathyroid hormone levels at least monthly during pregnancy. Perform fetal ultrasound for skeletal development and growth monitoring. Assess maternal renal function and blood pressure regularly. Consider amniotic fluid assessment for polyhydramnios if high doses are used. |
| Fertility Effects | No human data on fertility effects. In animal studies, high-dose parathyroid hormone has demonstrated adverse effects on reproductive indices including decreased fertility and impaired embryonic survival. Clinical significance in humans is unknown but caution is warranted in women of childbearing potential. |
| Clinical Pearls | NATPARA (parathyroid hormone) is a recombinant human PTH(1-84) used as an adjunct to calcium and vitamin D in hypoparathyroidism. Monitor serum calcium closely after initiation; adjust concomitant calcium and vitamin D doses to avoid hypercalcemia. Discontinue if serum calcium exceeds 12 mg/dL. Patients with renal impairment are at increased risk of hypercalcemia. Not recommended in patients with Paget's disease or skeletal metastases due to risk of osteosarcoma (based on animal studies). Store at 2-8°C; do not freeze. Administer via subcutaneous injection into the thigh using the provided pen device. |
| Patient Advice | NATPARA is used to increase low calcium levels by replacing parathyroid hormone. · You must take calcium and vitamin D supplements as directed; do not stop them unless instructed. · Inject NATPARA into the thigh exactly as prescribed, using a new needle each time. · Store the pen in the refrigerator at 2-8°C; do not freeze or shake. · Common side effects include nausea, diarrhea, and injection site reactions. · Report symptoms of high calcium: nausea, vomiting, constipation, muscle weakness, or confusion. · Avoid taking thiazide diuretics (e.g., hydrochlorothiazide) without doctor approval as they can raise calcium levels. · Do not use if you have Paget's disease, bone cancer, or have had radiation to bones. · Keep all appointments for blood tests to monitor calcium and kidney function. |