parathyroid hormone

General

**REMS Drug**

Pronunciation:
pa-ra-thye-royd hor-mone


Trade Name(s)

  • Natpara

Ther. Class.
electrolyte modifiers

Pharm. Class.
hormones

Indications

Adjunctive treatment (with calcium and vitamin D) in the management of hypocalcemia associated with hypoparathyroidism in patients who cannot be managed by calcium and active forms of Vitamin D alone.

Action

↑ serum calcium by ↑ renal tubular reabsorption, ↑ GI absorption of calcium (via activation of Vitamin D), and ↑ bone turnover (releases calcium).

Therapeutic Effect(s):

Normalization of serum calcium.

Pharmacokinetics

Absorption: Well absorbed (53%) following subcut administration.

Distribution: Unknown.

Metabolism and Excretion: Mostly metabolized by the liver, with some renal clearance.

Half-life: 2.8–3 hr.

TIME/ACTION PROFILE (↑ calcium)

ROUTEONSETPEAKDURATION
subcut2–3 hr10–12 hr> than 24 hr

Contraindication/Precautions

Contraindicated in:

  • Paget's disease of the bone, unexplained ↑alkaline phosphatase, children/young adults with open epiphyses, hereditary disorders predisposing to osteosarcoma, prior history of external beam/implant radiation therapy of the skeleton (may ↑ risk osteosarcoma)
  • Lactation: Discontinue parathyroid hormone or discontinue breastfeeding,

Use Cautiously in:

  • Concurrent use of digoxin
  • Severe hepatic or renal impairment
  • Geri: Initiate treatment at lower dose, consider age-related ↓ in renal, hepatic and cardiac function, concurrent disease states and drug therapies;
  • OB: Use during pregnancy only if potential benefit justifies potential risk to fetus
  • Pedi: Safe and effective use in children <18 yr has not been established.

Adverse Reactions/Side Effects

CNS: headache

CV: hypertension

GI: diarrhea, nausea, vomiting, upper abdominal pain

GU: hypercalciuria

F and E: HYPERCALCEMIA, HYPOCALCEMIA

MS: arthralgia, extremity pain, neck pain

Neuro: hypoaesthesia, paresthesia

Misc: potential risk of osteosarcoma

* CAPITALS indicate life-threatening.
Underline indicate most frequent.

Interactions

Drug-Drug

  • Hypercalcemia ↑ risk of digoxin toxicity; careful monitoring is recommended during concurrent use.
  • Concurrent doses of calcium supplements and active Vitamin D supplements will require adjustment during treatment.
  • Concurrent use with alendronate↓ calcium sparing effects and disrupts normalization of calcium; concurrent use is not recommended.

Route/Dosage

SC (Adults) 50 mcg once daily, frequent monitoring and adjustment may be necessary.

Availability

Lyophilized powder for subcutaneous injection (requires reconstitution) in dual chamber glass cartridges with diluent: 25 mcg, 50 mcg, 75 mcg, 100 mcg

Assessment

  • Monitor for signs and symptoms of hypercalcemia (nausea, vomiting, constipation, low energy, muscle weakness) or hypocalcemia (tingling of lips, tongue, fingers and feet, twitching of face muscles, cramping of feet and hands, seizures, depression, problems thinking or remembering) occur.

Lab Test Considerations: Prior to therapy, determine if 25-hydroxyvitamin D stores are sufficient; if not, replace to sufficient levels.

  • Prior to therapy, confirm serum calcium level is >7.5 mg/dL. Measure serum calcium within 3–7 days of starting therapy with parathyroid hormone.
  • Adjust doses of active vitamin D and/or calcium supplements based on serum calcium value and clinical assessments of hypocalcemia or hypercalcemia. If serum calcium level is >10.6 mg/dL (upper limit of normal), decrease or discontinue (if already at lowest dose) active form of vitamin D, then decrease calcium supplement. If serum calcium is >9 mg/dL and <10.6 mg/dL, decrease or discontinue (if already at lowest dose) active form of vitamin D, then no change to calcium supplement or decrease if active form of vitamin D has been discontinued. If serum calcium level is ≤9 mg/dL and >8 mg/dL, do not change either active form of vitamin D or calcium supplement dose. If serum calcium level is <8 mg/dL, increase active form of vitamin D, then increase calcium supplement. Continue to monitor serum calcium levels until target serum calcium levels are within lower half of normal range, active vitamin D has been discontinued and calcium supplementation is sufficient to meet daily requirements.
  • Parathyroid hormone doses may be ↑ in increments of 25 mcg every 4 wks to a maximum daily dose of 100 mcg if serum calcium cannot be maintained >8 mg/dL without active form of vitamin D and/or oral calcium supplementation. Parathyroid hormone dose can be ↓ as much as 25 mcg/day if total serum calcium level is >9 mg/dL and active form of vitamin D and calcium supplementation have been discontinued. Monitor clinical response as well as serum calcium following dose change. Monitor serum calcium and 24-hour urinary calcium once a maintenance dose is achieved.

Potential Diagnoses

Implementation

  • Parathyroid hormone is only available through a restricted program, NATPARA REMS Program. Only certified health care professionals can prescribe and certified pharmacies can dispense parathyroid hormone. Further information is available at www.natpararems.com or by calling 1-855-NATPARA or 1–855–628–7272.
    • When initiating parathyroid hormone, if patient is taking active form of vitamin D, decrease dose by 50% if serum calcium is >7.5 mg/dL.
    • If patient is taking calcium supplements, maintain calcium supplement dose when starting parathyroid hormone therapy.
  • SC Administer subcut into alternating thighs each day. Parathyroid hormone is supplied as a medication cartridge with powder and diluent for use with reusable mixing device and reusable Q-Cliq pen injector. Solution should be colorless but may contain small particles; do not administer discolored solutions. Cartridges can be stored in refrigerator for up to 14 days after reconstitution. Do not freeze or shake. Mixing device and empty Q-Cliq pen can be stored at room temperature.

Patient/Family Teaching

  • Instruct patient and caregiver in correct technique for subcut injection, use and disposal of equipment. Administer missed dose as soon as possible and take additional calcium supplementation if signs and symptoms of hypocalcemia occur. Advise patient to read Medication Guide before starting and with each Rx refill in case of changes.
  • Explain potential for developing hypocalcemia or hypercalcemia during dose adjustment. Instruct patient on signs and symptoms and advise to notify health care professional if signs and symptoms occur.
  • Inform patient of risk of osteosarcoma. Instruct patients to promptly notify health care professional if persistent localized pain or soft tissue masses tender to palpation occur; may signal osteosarcoma.
  • Advise patient to notify health care professional of all Rx or OTC medications, vitamins, or herbal products being taken and to consult with health care professional before taking other medications.
  • Advise female patient to notify health care professional if pregnancy is planned or suspected or if breastfeeding.

Evaluation/Desired Outcomes

Maintenance of total serum calcium (albumin-corrected) within lower half of the normal range (between 8 and 9 mg/dL) without need for active forms of vitamin D and with calcium supplementation sufficient to meet patient's daily requirements.

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