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Abiraterone; Uses, Dosage, Side Effects, Interactions

Abiraterone is an antiandrogen used to treat metastatic, castration-resistant prostate cancer. Abiraterone is associated with a not uncommon rate of serum enzyme elevation during therapy but has not been clearly linked to cases of clinically apparent liver injury with jaundice.

Abiraterone is a steroidal compound with antiandrogen activity. Abiraterone inhibits the enzymatic activity of steroid 17alpha-monooxygenase (17alpha-hydrolase/C17,20 lyase complex; CYP17A1), a member of the cytochrome p450 family that catalyzes the 17alpha-hydroxylation of steroid intermediates involved in testosterone synthesis. Administration of this agent may suppress testosterone production by both the testes and the adrenals to castrate-range levels.

Abiraterone acetate is a steroidal CYP17A1 inhibitor and by extension androgen synthesis inhibitor which is used in combination with prednisone in metastatic castration-resistant prostate cancer (previously called hormone-resistant or hormone-refractory prostate cancer) – i.e., prostate cancer not responding to androgen deprivation or treatment with androgen receptor antagonists. It is a prodrug to the active agent abiraterone.

Mechanism of action of Abiraterone

Abiraterone is an orally active inhibitor of the steroidal enzyme CYP17A1 (17 alpha-hydroxylase/C17,20 lyase). It inhibits CYP17A1 in a selective and irreversible manner via the covalent binding mechanism. CYP17A1 is an enzyme that catalyzes the biosynthesis of androgen and is highly expressed in testicular, adrenal, and prostatic tumor tissue. More specifically, abiraterone inhibits the conversion of 17-hydroxypregnenolone to dehydroepiandrosterone (DHEA) by the enzyme CYP17A1 to decrease serum levels of testosterone and other androgens.

Indications of Abiraterone

Prostate Cancer
Metastatic Castration-Resistant Prostate Cancer
Used in combination with prednisone for the treatment of metastatic, castration-resistant prostate cancer.

Contra-Indications of Abiraterone

Hyper sense. to drug/class/common.
Pregnancy
Uncontrolled or severe HTN
Hypokalemia
ALT >3x ULN and bilirubin >2x ULN
Hepatic impairment, Child-Pugh Class C
Hepatic impairment, Child-Pugh Class B
Cardiovascular dz or hx
Heart failure
Recent MI
Arrhythmias
Adrenal insufficiency

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Dosage of Abiraterone

Strengths: 250 mg; 500 mg

Prostate Cancer

1,000 mg orally once a day on an empty stomach (in combination with prednisone 5 mg orally 2 times a day)

Side Effects of Abiraterone

The most common

More common

Fast or irregular heartbeat
appetite loss
changes in nails
constipation
fatigue
fever
Back pain
dizziness
headache
increased cough
Acid or sour stomach
decreased appetite
Agitation
chest congestion
chest pain
cold sweats
confusion
decreased sexual ability or desire
stomach or abdominal cramps, gas, or pain
trouble sleeping

Less common

bleeding gums
blood in the urine or stools
chest pain
diarrhea
Burning, crawling, itching, numbness, prickling, “pins and needles“, or tingling feelings
difficulty in moving
muscle stiffness
redness of the face, neck, arms and occasionally, upper chest
lack or loss of strength
muscle spasm
difficult or labored breathing
dry mouth
headache
irritability
lack or loss of strength
loose stools
loss of interest or pleasure
muscle stiffness
night sweats
passing gas
stomach discomfort, upset, or pain
swollen joints
trouble concentrating
increased blood pressure

Drug Interactions of Abiraterone

Abiraterone acetate may interact with following drugs, supplements & may decrease the efficacy of the drug

alpha blockers (e.g., alfuzosin, doxazosin, silodosin, tamsulosin)
anticancer medications (e.g., cabazitaxel, docetaxel, doxorubicin, etoposide, ifosfamide, irinotecan, vincristine)
“azole” antifungal medications (e.g., fluconazole, itraconazole, ketoconazole)
beta-blockers (e.g., atenolol, propranolol, metoprolol)
barbiturates (e.g., butalbital, pentobarbital, phenobarbital)
benzodiazepines (e.g., chlordiazepoxide, clonazepam, diazepam, lorazepam)
calcium channel blockers (e.g., nifedipine, diltiazem, verapamil, amlodipine, felodipine)
carbamazepine
chloroquine
corticosteroids (e.g., dexamethasone, prednisone, methylprednisolone)
cyclosporine
dantrolene
“gliptin” diabetes medications (e.g., linagliptin, saxagliptin, sitagliptin)
HIV protease inhibitors (e.g., atazanavir, indinavir, ritonavir, saquinavir)
losartan
macrolide antibiotics (e.g., azithromycin, clarithromycin, erythromycin)
metronidazole
mirtazapine
montelukast
norfloxacin
ondansetron
carbamazepine
phenytoin
progestins (e.g., dienogest, levonorgestrel, medroxyprogesterone, norethindrone)
proton pump inhibitors (PPIs; e.g., esomeprazole, lansoprazole, omeprazole, pantoprazole, rabeprazole)
selective serotonin reuptake inhibitors (SSRIs; e.g., citalopram, duloxetine, fluoxetine,paroxetine, sertraline)
sildenafil
“statin” anticholesterol medications (e.g., atorvastatin, lovastatin, simvastatin)
tadalafil
tamoxifen
tetracycline
theophylline
tocilizumab
tolterodine
tramadol
other selective serotonin reuptake inhibitors (SSRIs; e.g., citalopram, fluoxetine, sertraline)
5-HT3 antagonists (e.g., granisetron, ondansetron)
tamsulosin
tapentadol
thiazide diuretics (e.g., hydrochlorothiazide, indapamide)
tramadol
tricyclic antidepressants (e.g., nortriptyline, amitriptyline, imipramine,
trimethoprim
other tyrosine kinase inhibitors (e.g., dasatinib, imatinib, nilotinib, sunitinib)
tetracycline
tocilizumab
vandetanib

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Pregnancy & Lactation of Abiraterone

FDA Pregnancy Category X

Pregnancy

Abiraterone should not be used by women. It is not known if abiraterone is found in semen. If you are engaged in sexual activity with a pregnant woman, a condom should be used. If you are engaged in sexual activity with a woman who may become pregnant, a condom and a second effective method of birth control should be used. Condoms must be used during treatment with abiraterone and for one week after treatment has ended.Due to the way that abiraterone works, it is possible that exposure to this medication during pregnancy may harm the developing baby. To prevent accidental exposure to abiraterone, women who handle these tablets should wear gloves.

Lactation

Abiraterone should not be used by women. It is not known if abiraterone passes into breast milk. To prevent accidental exposure to abiraterone, women who handle these tablets should wear gloves. The safety and effectiveness of using this medication have not been established for children.