パリカルシトール

パリカルシトール（化学的には19-ノル-1,25-(OH)₂-ビタミンD₂である。Abbott Laboratoriesからゼンプラールの商品名で販売されている）は、慢性腎不全に伴う二次性副甲状腺機能亢進症（副甲状腺ホルモンの過剰分泌）の予防と治療に用いられる医薬品である。ビタミンD₂（エルゴカルシフェロール）の活性型である1,25-ジヒドロキシエルゴカルシフェロールの類似体である。

Paricalcitol/ja

Clinical data
Trade names	Zemplar
Other names	(1R,3S)-5-[2-[(1R,3aR,7aS)-1-[(2R,5S)-6-hydroxy-5,6-dimethyl-3E-hepten-2-yl]-7a-methyl-2,3,3a,5,6,7-hexahydro-1H-inden-4-ylidene]ethylidene]-cyclohexane-1,3-diol
AHFS/Drugs.com	Monograph
MedlinePlus	a682335
Pregnancy category	AU: C
Routes of administration	Oral, Intravenous
ATC code	H05BX02 (WHO)
Legal status
Legal status	AU: S4 (Prescription only) CA: ℞-only UK: POM (Prescription only) US: ℞-only
Pharmacokinetic data
Bioavailability	72%
Protein binding	99.8%
Metabolism	Hepatic
Elimination half-life	14-20 hours
Excretion	Faeces (74%), urine (16%)
Identifiers
IUPAC name (1R,3R,7E,17β)-17-[(1R,2E,4S)-5-hydroxy-1,4,5-trimethylhex-2-en-1-yl]-9,10-secoestra-5,7-diene-1,3-diol
CAS Number	131918-61-1 Y
PubChem CID	5281104
IUPHAR/BPS	2791
DrugBank	DB00910 N
ChemSpider	4444552 Y
UNII	6702D36OG5
KEGG	D00930 N
ChEBI	CHEBI:7931 N
ChEMBL	ChEMBL1200622 Y
Chemical and physical data
Formula	C27H44O3
Molar mass	416.646 g·mol−1
InChI InChI=1S/C27H44O3/c1-18(8-9-19(2)26(3,4)30)24-12-13-25-21(7-6-14-27(24,25)5)11-10-20-15-22(28)17-23(29)16-20/h8-11,18-19,22-25,28-30H,6-7,12-17H2,1-5H3/b9-8+,21-11+/t18-,19+,22-,23-,24-,25+,27-/m1/s1 Y Key:BPKAHTKRCLCHEA-UBFJEZKGSA-N Y
NY (what is this?)  (verify)

1989年に特許を取得し、1998年に医療用として承認された。

医薬用途

医療における主な用途は、慢性腎臓病に伴う二次性副甲状腺機能亢進症の治療である。しかし、現在のところ、この適応症に対する非選択的ビタミンD誘導体に対するパリカルシトールの優位性を示す証拠は十分ではない。

副作用

頻度別の副作用：
非常に多い（頻度10％以上）:

• 吐き気

一般的（頻度1～10％）:

• 下痢^†
• 浮腫
• アレルギー反応
• 関節炎
• めまい^†
• 胃の不快感^†
• 胃食道逆流症^†
• ニキビ^†
• 高カルシウム血症^†
• 低カルシウム血症^†
• 高リン血症
• 食欲減退^†
• 頭痛
• 乳房圧痛^†
• 味覚変化
• 副甲状腺機能低下症
• めまい
• 発疹^‡</sup

Uncommon (0.1-1% frequency):

• Abnormal hepatic enzymes^‡
• Constipation^‡
• Dry mouth^‡
• Itchiness^‡
• Hives
• Hypersensitivity^‡
• Muscle spasms^‡
• Bleeding time prolonged
• Aspartate aminotransferase increased
• Laboratory test abnormal
• Weight loss
• Elevated blood creatinine
• Cardiac arrest
• Arrhythmia
• Atrial flutter
• Anaemia
• Leucopenia
• Lymphadenopathy
• Coma
• Stroke
• Transient ischemic attack
• Fainting
• Myoclonus
• Hypoaesthesia
• Paraesthesia
• Glaucoma
• Conjunctivitis
• Ear disorder
• Pulmonary oedema
• Asthma
• Shortness of breath
• Nose bleed
• Cough
• Rectal haemhorrhage
• Colitis
• Gastritis
• Indigestion
• Difficulty swallowing
• Gastrointestinal disorder
• Gastrointestinal haemorrhage
• Bullous dermatitis
• Hair loss
• Hirsutism
• Hyperhidrosis
• Joint pain
• Joint stiffness
• Back pain
• Muscle twitching
• Muscle aches
• Hyperparathyroidism
• Hyperkalaemia
• Hypocalcemia
• Breast cancer
• Sepsis
• Pneumonia
• Infection
• Pharyngitis
• Vaginal infection
• Influenza
• High blood pressure
• Hypotension
• Gait disturbance
• Injection site pain
• Fever
• Chest pain
• Condition aggravated
• Muscle weakness
• Malaise
• Thirst
• Breast pain
• Impotence
• Confusional state
• Delirium
• Depersonalization
• Agitation
• Insomnia
• Nervousness

^‡ These are adverse effects only seen in patients with grade 3 or 4 chronic kidney disease. ^† These are adverse effects only seen in patients with grade 5 chronic kidney disease.

Contraindications

Contraindications include:

• Vitamin D intoxication
• Hypercalcaemia
• Hypersensitivity to paricalcitol or any of its excipients

whereas cautions include:

• Impaired liver function
• It is also advised that physicians regularly monitor their patients' calcium and phosphorus levels.

Interactions

Drugs that may interact with paricalcitol include:

• Ketoconazole, as it may interfere with paricalcitol's metabolism in the liver.
• Digitoxin, hypercalcaemia due to any cause can exacerbate the toxicity of digitoxin.
• Thiazide diuretics or calcium supplements as hypercalcaemia may be induced by this combination
• Magnesium-containing products such as antacids may increase the risk of hypermagnesemia.
• Aluminium-containing products such as antacids may increase the risk of aluminium toxicity.
• Drugs that interfere with the absorption of fat-soluble vitamins, such as cholestyramine may interfere with the absorption of paricalcitol.

Overdose

Electrolyte abnormalities (e.g. hypercalcaemia and hyperphosphataemia) are common overdose symptoms. Treatment is mostly supportive, with particular attention being paid to correcting electrolyte anomalies and reducing intake of calcium in both the form of supplementation and diet. As it is so heavily bound to plasma proteins haemodialysis is unlikely to be helpful in cases of overdose.

Early symptoms of overdose can include:

• Weakness
• Headache
• Somnolence
• Nausea
• Vomiting
• Dry mouth
• Constipation
• Muscle pain
• Bone pain
• Metallic taste in the mouth.

It is worth noting, however, that may of these symptoms are also indicative of kidney failure and hence may be masked by the patient's condition.

Late symptoms of overdose include:

• Loss of appetite
• Weight loss
• Conjunctivitis (calcific)
• Pancreatitis
• Photophobia
• Rhinorrhoea
• Pruritus
• Hyperthermia
• Decreased libido
• Elevated BUN
• Hypercholesterolaemia
• Elevated AST and ALT
• Ectopic calcification
• Hypertension
• Cardiac arrhythmias
• Somnolence
• Death
• Psychosis (rare)

作用機序

パリカルシトールの3次元構造

1,25-ジヒドロキシエルゴカルシフェロールと同様に、パリカルシトールはビタミンD受容体でアゴニストとして作用し、それによって血中の副甲状腺ホルモン濃度を低下させる。

薬物動態

パリカルシトールの血漿中濃度は、初回静脈内投与後2時間以内に急速に対数直線的に減少する。したがって、パリカルシトールの投与頻度は通常1日おき（週3回）以下であるため、複数回の投与による蓄積は期待できない。