Parathyroid Hormone

The dosing of Parathyroid Hormone must be highly individualized to maintain the patient's serum calcium in the lower half of the normal range. According to clinical guidelines, the starting dose is typically 50 mcg once daily, administered subcutaneously in the thigh.

Before starting treatment, your healthcare provider will ensure your 25-hydroxyvitamin D stores are sufficient and that your serum calcium is above 7.5 mg/dL. When starting Parathyroid Hormone, the doses of active vitamin D and oral calcium supplements are usually reduced by 50% to prevent hypercalcemia (excessively high blood calcium). Your doctor will monitor your blood calcium levels frequently (e.g., every 3 to 7 days) during the initial titration phase and adjust the hormone dose in increments of 25 mcg every 4 weeks if necessary. The maintenance range is generally 25 mcg to 100 mcg once daily.

Parathyroid Hormone is NOT approved for use in pediatric patients. The safety and effectiveness in children and adolescents have not been established. There is a specific concern regarding the risk of osteosarcoma in pediatric populations, as their bones are still growing (open epiphyses). In animal studies, increased bone turnover in young rats led to a higher incidence of bone tumors.

Renal Impairment

No specific dose adjustment is required for patients with mild to moderate renal impairment. However, because Parathyroid Hormone affects renal calcium and phosphate handling, patients with significant kidney disease require close monitoring of their calcium-phosphate product to prevent soft tissue calcification.

Hepatic Impairment

No dose adjustment is required for patients with mild to moderate hepatic impairment (Child-Pugh Class A or B). The drug has not been studied in patients with severe hepatic impairment.

Elderly Patients

Clinical trials did not include sufficient numbers of patients aged 65 and over to determine if they respond differently than younger patients. In general, dose selection for an elderly patient should be cautious, starting at the low end of the dosing range.

1. 1Preparation: The medication comes in a dual-chamber cartridge that must be mixed using the provided injection pen. Follow the manufacturer's 'Instructions for Use' carefully to ensure the powder is fully dissolved.
2. 2Administration: Inject the dose subcutaneously into the thigh. Rotate injection sites (left thigh vs. right thigh) each day.
3. 3Timing: Take the dose at the same time every day.
4. 4Storage: Before reconstitution, store the cartridges in the refrigerator (36°F to 46°F). After mixing, the cartridge must be kept in the refrigerator and used within 14 days. Do not freeze the medication.
5. 5Swallow vs. Crush: This is an injectable protein medication; it cannot be swallowed, crushed, or taken orally, as stomach acid would destroy the hormone before it could be absorbed.

If you miss a dose, take it as soon as you remember. However, if it is almost time for your next scheduled dose, skip the missed dose and return to your regular schedule. Do not take two doses on the same day. If you miss more than two consecutive doses, contact your healthcare provider, as your calcium levels may drop rapidly, requiring temporary increases in your oral calcium and vitamin D supplements.

Signs of overdose (hypercalcemia) include severe nausea, vomiting, constipation, muscle weakness, and confusion. In severe cases, it can lead to kidney stones or heart rhythm abnormalities. If an overdose is suspected, seek emergency medical attention immediately. Treatment typically involves vigorous hydration and discontinuation of the hormone until calcium levels stabilize.

> Important: Follow your healthcare provider's dosing instructions exactly. Do not adjust your dose or stop the medication without medical guidance, as sudden discontinuation can lead to life-threatening hypocalcemia.

In clinical trials, the most frequently reported side effects associated with Parathyroid Hormone therapy include:

• Paresthesia (Tingling sensations): Often felt in the hands, feet, or around the mouth. This is frequently a sign of fluctuating calcium levels.
• Hypocalcemia (Low blood calcium): Paradoxically, if a dose is missed or during the initial adjustment phase, calcium can drop, causing muscle cramps and 'pins and needles.'
• Headache: Usually mild to moderate and may diminish as the body adjusts to the hormone.
• Nausea: Some patients report mild stomach upset shortly after injection.
• Arthralgia (Joint pain): General aching in the joints is common during the first few months of therapy.

• Hypercalcemia (High blood calcium): This occurs if the dose is too high. Symptoms include increased thirst, frequent urination, and fatigue.
• Upper respiratory tract infections: Some patients may experience symptoms similar to a common cold.
• Abdominal pain: Discomfort in the stomach area.
• Injection site reactions: Redness, swelling, or itching where the needle entered the skin.

• Severe Hypercalciuria: Excess calcium in the urine, which can increase the risk of kidney stones.
• Hypomagnesemia: Low magnesium levels in the blood, which can exacerbate muscle spasms.
• Allergic Dermatitis: Skin rashes or hives related to the injection.

> Warning: Stop taking Parathyroid Hormone and call your doctor immediately if you experience any of these serious conditions:

• Severe Hypercalcemia: Symptoms include extreme thirst, confusion, 'brain fog,' severe constipation, and cardiac arrhythmias (irregular heartbeat). This is a medical emergency that can lead to kidney failure.
• Severe Hypocalcemia (Tetany): If you experience uncontrollable muscle spasms, seizures, or a 'choking' sensation (laryngospasm), seek emergency care immediately. This often occurs if the medication is stopped abruptly.
• Osteosarcoma Risk Signals: While not yet observed in humans during clinical trials, any new, persistent bone pain or unexplained lumps should be reported immediately, given the black box warning for bone cancer.
• Anaphylaxis: Though rare, signs of a severe allergic reaction include swelling of the face/tongue, difficulty breathing, and a rapid drop in blood pressure.

Long-term use of Parathyroid Hormone requires monitoring for bone health and kidney function. Because the hormone stimulates bone turnover, there is a theoretical risk of changing bone mineral density over many years. Additionally, chronic fluctuations in calcium and phosphate can lead to 'ectopic calcification' (calcium deposits in soft tissues like the kidneys or brain) if not managed precisely.

WARNING: POTENTIAL RISK OF OSTEOSARCOMA

In male and female rats, parathyroid hormone caused an increase in the incidence of osteosarcoma (a malignant bone tumor). The occurrence of osteosarcoma was dependent on the dose and the duration of treatment. Because the relevance of these rat findings to humans is unknown, Parathyroid Hormone should be prescribed only to patients with hypoparathyroidism who cannot be well-controlled on standard therapy and for whom the potential benefits outweigh the potential risk of osteosarcoma. Avoid use in patients who are at increased baseline risk for osteosarcoma, such as those with Paget’s disease of bone, open epiphyses (pediatric patients), or prior external beam or implant radiation therapy involving the skeleton.

Report any unusual symptoms or side effects to your healthcare provider immediately. Regular blood work is mandatory to ensure your safety while on this medication.

Parathyroid Hormone is a high-alert medication that requires diligent monitoring. It is not a simple 'vitamin' but a potent hormone that fundamentally changes how your body handles minerals. Patients must be committed to regular blood testing and must understand the signs of both high and low calcium.

No FDA black box warnings for Parathyroid Hormone?** No, this is incorrect. **There IS a Black Box Warning.

Full Text Summary: Parathyroid Hormone is associated with a potential risk of osteosarcoma. In animal studies (rats), the drug caused a significant increase in bone cancer. While this has not been confirmed in humans, the drug is only available through the Natpara REMS Program. Use is restricted to patients where the benefits clearly outweigh the risks of potential malignancy. It must be avoided in patients with Paget’s disease, unexplained elevations of alkaline phosphatase, or those who have had prior radiation therapy to the bones.

• Hypercalcemia Risk: The most significant acute risk is excessively high blood calcium. This can occur during dose escalation or if oral calcium/vitamin D doses are not reduced appropriately when starting the hormone. Severe hypercalcemia can cause permanent kidney damage and life-threatening heart rhythm issues.
• Hypocalcemia Risk: If the medication is stopped suddenly, or if a dose is missed, blood calcium can crash to dangerously low levels. This is because the body's own parathyroid glands are not working, and the 'external' source of hormone has been removed.
• Digoxin Toxicity: High calcium levels increase the risk of digitalis toxicity. Patients taking Digoxin (Lanoxin) must be monitored with extreme care.
• Concomitant Bone Disease: Patients with pre-existing bone conditions (other than hypoparathyroidism-related changes) must be evaluated for the risk of bone cancer before starting therapy.

While taking Parathyroid Hormone, you will need frequent laboratory tests, including:

• Serum Total Calcium: Initially every few days, then monthly, then every 3-6 months once stable.
• Serum Phosphorus: To ensure phosphate levels remain within a safe range.
• 25-hydroxyvitamin D: To ensure your body has enough 'raw material' for the hormone to work.
• Urinary Calcium: 24-hour urine collections may be needed to check for hypercalciuria (excess calcium in urine), which causes kidney stones.
• Creatinine/BUN: To monitor kidney function.

Parathyroid Hormone generally does not affect the ability to drive. However, if you experience symptoms of hypocalcemia (such as dizziness or muscle twitching) or hypercalcemia (such as confusion), you should avoid operating heavy machinery until your calcium levels are stabilized.

There is no direct chemical interaction between alcohol and Parathyroid Hormone. However, excessive alcohol consumption can interfere with calcium absorption and worsen dehydration, which increases the risk of kidney stones. It is best to limit alcohol intake to moderate levels.

NEVER stop taking Parathyroid Hormone abruptly. If you must stop the medication, your doctor will implement a 'taper-up' strategy for your oral calcium and vitamin D supplements. Without the hormone, your calcium levels will drop rapidly, often within 24 to 48 hours, which can lead to seizures or tetany.

> Important: Discuss all your medical conditions, especially any history of bone disease or radiation therapy, with your healthcare provider before starting Parathyroid Hormone.

There are no absolute 'never use' drug-drug contraindications listed in the FDA labeling; however, the use of Teriparatide (Forteo) or other PTH analogs alongside Parathyroid Hormone is contraindicated because it would lead to an unpredictable and dangerous additive effect on calcium levels.

• Digoxin (Lanoxin): This is the most critical interaction. Parathyroid hormone increases serum calcium. High calcium (hypercalcemia) predisposes the heart to the toxic effects of Digoxin, which can lead to fatal arrhythmias. If you take Digoxin, your doctor will monitor your calcium and ECG very closely.
• Thiazide Diuretics (e.g., Hydrochlorothiazide, Chlorthalidone): These 'water pills' reduce the amount of calcium excreted in the urine. When combined with Parathyroid Hormone, the risk of developing hypercalcemia is significantly increased.
• Lithium: Lithium can sometimes increase parathyroid hormone levels or interfere with calcium sensing. Combining it with rhPTH requires frequent monitoring of mineral levels.

• Alendronate and other Bisphosphonates: Some studies suggest that taking bisphosphonates (for bone density) at the same time as parathyroid hormone may slightly reduce the hormone's effectiveness in raising blood calcium. The clinical significance is still being debated.
• Systemic Corticosteroids (e.g., Prednisone): Steroids can deplete calcium levels and interfere with vitamin D metabolism, potentially requiring higher doses of Parathyroid Hormone to achieve the same effect.

• High-Calcium Foods: While you need calcium, a sudden, massive increase in dietary calcium (e.g., suddenly eating large amounts of cheese or yogurt) can cause a spike in blood calcium when combined with the hormone.
• Caffeine: Excessive caffeine can slightly increase calcium excretion in the urine, though this is usually not clinically significant for most patients.
• Hydration: It is vital to stay well-hydrated. Dehydration increases the concentration of calcium in the blood and kidneys, raising the risk of toxicity and stones.

• Vitamin D Supplements: You will likely be taking Vitamin D as part of your regimen. However, taking 'extra' high-dose Vitamin D supplements without your doctor's knowledge can lead to vitamin D toxicity and severe hypercalcemia.
• Calcium Carbonate/Citrate: These are necessary, but the timing and dosage must be strictly controlled by your doctor. Changing brands or doses can disrupt your calcium balance.
• Magnesium Supplements: Low magnesium can prevent Parathyroid Hormone from working correctly. Your doctor may recommend a magnesium supplement, but it must be balanced.

Parathyroid Hormone treatment will naturally affect the results of several lab tests:

• Alkaline Phosphatase: May increase as bone turnover increases.
• 1,25-dihydroxyvitamin D: Levels will rise because the hormone stimulates its production.
• Serum Phosphate: Levels should decrease as the hormone promotes renal excretion.

> Important: Tell your doctor about ALL medications, supplements, and herbal products you are taking. Even 'natural' supplements can have profound effects on your mineral balance.

Parathyroid Hormone must NEVER be used in the following circumstances:

1. 1Hypersensitivity: Patients with a known severe allergy to recombinant human parathyroid hormone or any of the excipients in the injection (such as mannitol or metacresol). Anaphylaxis is a rare but absolute contraindication.
2. 2Pediatric Patients: Due to the risk of osteosarcoma in growing bones, the drug is absolutely contraindicated in children and adolescents with open epiphyses.
3. 3Paget’s Disease of Bone: This condition involves abnormal bone recycling. Patients with Paget’s are at a much higher risk for developing bone cancer (osteosarcoma) when exposed to parathyroid hormone.
4. 4Prior Bone Radiation: Anyone who has received external beam or implant radiation therapy involving the skeleton should not use this drug, as radiation is a known risk factor for osteosarcoma.
5. 5Bone Malignancies: Patients with existing bone cancer or cancer that has spread (metastasized) to the bone.

These conditions require a careful risk-benefit analysis by a specialist:

• Pregnancy and Lactation: Because the effects on the fetus and nursing infant are not well-understood, use is only recommended if the benefit to the mother clearly outweighs the risk to the child.
• Severe Renal Impairment: While not an absolute contraindication, the risk of mineral imbalances and soft tissue calcification is much higher.
• Active Nephrolithiasis (Kidney Stones): Since the hormone changes how calcium is excreted, it may worsen active stone disease.

There is a potential for cross-sensitivity with other parathyroid hormone analogs like Teriparatide (Forteo) or Abaloparatide (Tymlos). If you have had a severe allergic reaction to those drugs, you should not use Parathyroid Hormone (rhPTH 1-84).

> Important: Your healthcare provider will evaluate your complete medical history, including any history of cancer or radiation, before prescribing Parathyroid Hormone.

Parathyroid Hormone is classified as Pregnancy Category C (under the older FDA system). There are no adequate and well-controlled studies in pregnant women. Animal studies have shown some developmental delays in offspring when mothers were given high doses. In clinical practice, if a woman with hypoparathyroidism becomes pregnant, her calcium needs will change significantly, especially in the third trimester. Most experts recommend managing calcium with active vitamin D and calcium supplements rather than the hormone during pregnancy unless the condition is otherwise unmanageable.

It is unknown whether Parathyroid Hormone is excreted in human milk. Because many drugs are excreted in milk and because of the potential for serious adverse reactions in nursing infants (including effects on the infant's own calcium regulation), a decision should be made whether to discontinue nursing or discontinue the drug, taking into account the importance of the drug to the mother.

Safety and effectiveness have not been established in patients less than 18 years of age. The drug is strictly avoided in this population due to the risk of osteosarcoma during periods of active bone growth. If a child has hypoparathyroidism, they are typically managed with conventional therapy (calcium and calcitriol) rather than rhPTH 1-84.

Clinical studies of Parathyroid Hormone did not include enough subjects aged 65 and over to determine whether they respond differently than younger subjects. In general, elderly patients have a higher prevalence of decreased renal function and are more likely to be taking concurrent medications like Digoxin or diuretics. Therefore, dose titration should be slower, and monitoring of calcium and kidney function should be more frequent.

For patients with mild to moderate renal impairment (Creatinine Clearance 30 to 80 mL/min), no specific starting dose adjustment is needed. However, these patients are at a higher risk for 'calcium-phosphate product' elevation, which can lead to calcification of the kidneys (nephrocalcinosis). For patients with severe renal impairment or those on dialysis, the drug should be used with extreme caution, as the pharmacokinetics have not been fully studied in this group.

In patients with mild to moderate hepatic impairment, the peak concentration and total exposure to the drug are slightly lower, but not enough to require a dose adjustment. There is no data available for patients with severe hepatic impairment (Child-Pugh Class C). Since the liver is a site of peptide cleavage, these patients should be monitored closely if the drug is initiated.

> Important: Special populations require individualized medical assessment and frequent lab monitoring to ensure the safety of both the patient and, in the case of pregnancy, the developing fetus.

Parathyroid Hormone (rhPTH 1-84) is a bone-active agent that serves as a potent agonist at the PTH1 Receptor (PTH1R), a G-protein coupled receptor. Upon binding to PTH1R in bone and kidney tissues, it triggers two primary intracellular signaling pathways: the adenylate cyclase/cyclic AMP (cAMP) pathway and the phospholipase C/inositol triphosphate pathway.

In the kidney, this activation leads to increased expression of calcium transporters in the distal tubule (enhancing reabsorption) and down-regulation of phosphate transporters in the proximal tubule (enhancing excretion). In the bone, the hormone stimulates the RANKL pathway, which regulates the balance between bone resorption and formation. Unlike Teriparatide (which is only the 1-34 fragment), rhPTH 1-84 is the full-length molecule, which may have additional effects mediated by C-terminal PTH receptors, though the clinical significance of this is still being researched.

Following a single subcutaneous injection, serum calcium levels begin to rise within 2 hours and reach a peak effect at approximately 10 to 12 hours. The effect on calcium typically lasts for 24 hours, which is why once-daily dosing is standard. The drug also causes a rapid decrease in serum phosphorus levels. Over time, chronic administration helps stabilize the 'calcium-sensing' mechanism of the body, though it does not cure the underlying parathyroid gland failure.

| Parameter | Value |

|---|---|

| Bioavailability | ~53% (Subcutaneous) |

| Protein Binding | Low (primarily circulates freely) |

| Half-life | ~3 hours (Terminal) |

| Tmax | 5 to 30 minutes |

| Metabolism | Hepatic and systemic proteolysis |

| Excretion | Minimal renal excretion of intact protein |

• Molecular Formula: C408H674N126O126S2
• Molecular Weight: Approximately 9425 Daltons
• Structure: A single-chain polypeptide consisting of 84 amino acids. It is produced using recombinant DNA technology in a modified strain of Escherichia coli.
• Solubility: Soluble in water and aqueous buffers at physiological pH.

Parathyroid Hormone is the flagship member of the Parathyroid Hormone [EPC] class. It is distinct from 'bisphosphonates' (which inhibit bone breakdown) and 'calcimimetics' (which lower PTH). It is a true hormone replacement therapy, similar in concept to using insulin for diabetes or levothyroxine for hypothyroidism.