{{위키데이터 속성 추적}}
'''생물학적 반감기'''(生物學的半減期, {{llang|en|biological half-life}})는 [[방사성 물질]]이나 [[약|약물]] 따위의 물질이 생물의 몸 속에서 절반으로 줄어드는 데 걸리는 시간이다. 일반적으로 물질의 [[혈장]] 농도가 최대혈장농도(C<sub>max</sub>)의 절반으로 줄어드는 시간을 통해 측정하며<ref>{{웹 인용|url=https://sites.google.com/site/pharmacologyinonesemester/2-drug-distribution-metabolism-and-elimination/2-5-blood-levels/2-5-2-elimination-half-life |title=Pharmacology in one semester |access-date=20 February 2020 |archive-date=22 October 2020 |archive-url=https://web.archive.org/web/20201022081736/https://sites.google.com/site/pharmacologyinonesemester/2-drug-distribution-metabolism-and-elimination/2-5-blood-levels/2-5-2-elimination-half-life |url-status=dead }}</ref><ref name="AIDSinfo 2020">{{웹 인용 | title=Half-Life (t½) Definition | website=AIDSinfo | date=2020-02-19 | url=https://aidsinfo.nih.gov/understanding-hiv-aids/glossary/286/half-life | access-date=2020-02-20 | archive-date=2020-02-20 | archive-url=https://web.archive.org/web/20200220040435/https://aidsinfo.nih.gov/understanding-hiv-aids/glossary/286/half-life | url-status= }}</ref><ref name="Curry 1993 pp. 127–144">{{서적 인용| last=Curry | first=Stephen H. | title=Antipsychotic Drugs and their Side-Effects | chapter=PHARMACOKINETICS OF ANTIPSYCHOTIC DRUGS | publisher=Elsevier | year=1993 | isbn=978-0-12-079035-7 | doi=10.1016/b978-0-12-079035-7.50015-4 | pages=127–144 | quote=The elimination half-life measures the kinetics of loss of drug from the body as a whole once all distribution equilibria have been achieved.}}</ref><ref name="Dasgupta Krasowski 2020 pp. 1–17">{{서적 인용| last1=Dasgupta | first1=Amitava | last2=Krasowski | first2=Matthew D. | title=Therapeutic Drug Monitoring Data | chapter=Pharmacokinetics and therapeutic drug monitoring | publisher=Elsevier | year=2020 | isbn=978-0-12-815849-4 | doi=10.1016/b978-0-12-815849-4.00001-3 | pages=1–17 | quote=The half-life of a drug is the time required for the serum concentration to be reduced by 50%. Once the half-life of the drug is known, the time required for clearance can be estimated. Approximately 97% of the drug is eliminated by 5 halflives, while ~99% is eliminated by 7 half-lives. }}</ref><ref>{{저널 인용| journal= Journal of Veterinary Pharmacology and Therapeutics| volume=27 | issue=6 | pages=427–439 | date=2004 | quote=Following i.v. administration, the terminal half-life is the time required for plasma/blood concentration to decrease by 50% after pseudo-equilibrium of distribution has been reached; then, terminal half-life is computed when the decrease in drug plasma concentration is due only to drug elimination, and the term ‘elimination half-life’ is applicable. Therefore, it is not the time necessary for the amount of the administered drug to fall by one half.| doi=10.1111/j.1365-2885.2004.00600.x | pmid=15601438 | title=Plasma terminal half-life | last1=Toutain | first1=P. L. | last2=Bousquet-Melou | first2=A. | archive-url=https://web.archive.org/web/20200220042629/http://physiologie.envt.fr/wp-content/uploads/2016/06/Plasma_terminal_half-life.pdf |url=http://physiologie.envt.fr/wp-content/uploads/2016/06/Plasma_terminal_half-life.pdf| archive-date=2020-02-20 }}</ref> 기호로는 <math>t_{\frac{1}{2}}</math>로 나타낸다.<ref name="AIDSinfo 2020"/><ref name="Dasgupta Krasowski 2020 pp. 1–17"/>

생물학적 반감기는 [[대사물질]], 약물, 신호전달물질 따위가 몸에서 얼마나 빨리 없어지는지 아는 데 쓰인다. 일반적으로 생물학적 반감기는 [[간]]의 대사작용과 대소변을 통한 배출 등 신체의 자연스러운 기능에 관한 것이다. 반감기의 개념은 물질의 양이 대략 [[지수함수]]적으로 감소할 때 쓰인다.<ref>{{GoldBookRef|title=Biological Half Life|file=B00658}}</ref>

의학의 맥락에서 생물학적 반감기는 어느 물질이 생명체의 혈액 전체를 순환하고 있을 때 물질의 [[혈장]] 속 농도가 절반으로 줄어드는 시간, 즉 '''혈장 반감기'''를 가리킨다. 이 측정값은 어떤 약물의 평균 혈중 농도를 일정하게 유지해야 할 때 약물을 얼마나 많이, 얼마나 자주 투여해야 할지 결정하는 데 도움을 주기 때문에 의학·[[약학]]·[[약물동태학]]에서 중요하게 쓰인다.

생물학적 반감기와 혈장 반감기의 관계는 약물의 특성에 따라 조직 내 축적(혈장단백결합), 활성 대사물질, 수용체 상호작용 등의 여러 요인이 개입하여 다소 복잡할 수 있다.<ref name="SCM">{{서적 인용|title=Spinal Cord Medicine|author1=Lin VW|author2=Cardenas DD|publisher=Demos Medical Publishing, LLC|page=251|url=https://books.google.com/books?id=3anl3G4No_oC&pg=PA251|year=2003|isbn=1-888799-61-7}}</ref>

== 예시 ==
=== 주요 처방약 ===
{| class="wikitable"
! 물질 !! 생물학적 반감기
|-
|[[아데노신]]||10초 미만(추정)<ref>{{서적 인용|title=Austria-Codex| veditors = Haberfeld H |at=Adenosin Baxter3 mg/ml Injektionslösung|publisher=Österreichischer Apothekerverlag|location=Vienna|year=2020|language=German}}</ref>
|-
|[[노르에피네프린]]||2분<ref>{{서적 인용|title=Austria-Codex| veditors = Haberfeld H |at=Noradrenalin Orpha 1 mg/ml Konzentrat zur Herstellung einer Infusionslösung|publisher=Österreichischer Apothekerverlag|location=Vienna|year=2020|language=German}}</ref>
|-
|[[옥살리플라틴]]||14분<ref>{{저널 인용|last=Ehrsson |first=Hans |url=http://journals.humanapress.com/index.php?option=com_opbookdetails&task=articledetails&category=humanajournals&article_code=MO:19:4:261 |title=Pharmacokinetics of oxaliplatin in humans |journal=Medical Oncology |volume=19 |issue=4 |pages=261–5 |date=Winter 2002 |access-date=2007-03-28 |display-authors=etal |url-status=dead |archive-url=https://web.archive.org/web/20070928104657/http://journals.humanapress.com/index.php?option=com_opbookdetails&task=articledetails&category=humanajournals&article_code=MO%3A19%3A4%3A261 |archive-date=2007-09-28 |pmid=12512920 |doi=10.1385/MO:19:4:261 |s2cid=1068099 }}</ref>
|-
|[[잘레플론]]||1시간<ref>Zaleplon {{Drugs.com|monograph|zaleplon}}. Accessed 15 April 2021.</ref>
|-
|[[모르핀]]||1.5 ~ 4.5시간<ref>Morphine {{Drugs.com|monograph|morphine}}. Accessed 15 April 2021.</ref>
|-
|[[플루라제팜]]
|2.3시간<ref name="flurazepam">Flurazepam {{Drugs.com|monograph|flurazepam}}. Accessed 15 April 2021.</ref>
활성 대사물질([[N-데살킬플루라제팜]]): 47 ~ 100시간<ref name="flurazepam" />
|-
|[[메토트렉세이트]]||3 ~ 10시간(저용량),
8 ~ 15시간(고용량)<ref>{{웹 인용|url=http://reference.medscape.com/drug/trexall-methotrexate-343201#showall|title=Trexall, Otrexup (methotrexate) dosing, indications, interactions, adverse effects, and more|website=reference.medscape.com}}</ref>
|-
|[[메타돈]]||15 ~ 72시간
드물게 최대 8일<ref>{{저널 인용 |last=Manfredonia |first=John |url=http://www.jaoa.org/cgi/content/full/105/3_suppl/18S |title=Prescribing Methadone for Pain Management in End-of-Life Care |journal=Journal of the American Osteopathic Association |volume=105 |date=March 2005 |issue=3 supplement |pages=S18-21 |access-date=2007-01-29 |pmid=18154194 |archive-date=2007-05-20 |archive-url=https://web.archive.org/web/20070520062222/http://www.jaoa.org/cgi/content/full/105/3_suppl/18S |url-status= }}</ref>
|-
|[[디아제팜]]||20 ~ 50시간<ref name="diazepam">Diazepam {{Drugs.com|monograph|diazepam}}. Accessed 15 April 2021.</ref>
활성 대사물질([[노르다제팜]]): 30 ~ 200시간<ref name="diazepam" />
|-
|[[페니토인]]||20 ~ 60시간<ref>{{서적 인용|title=Austria-Codex| veditors = Haberfeld H |at=Epilan D 100 mg-Tabletten|publisher=Österreichischer Apothekerverlag|location=Vienna|year=2020|language=German}}</ref>
|-
|[[부프레노르핀]]||28 ~ 35시간<ref>Buprenorphine {{Drugs.com|monograph|buprenorphine}}. Accessed 15 April 2021.</ref>
|-
|[[클로나제팜]]||30 ~ 40시간<ref>{{웹 인용 |url=https://www.gene.com/download/pdf/klonopin_prescribing.pdf |title=Klonopin (clonazepam) Prescribing Guide |date=October 2017 |publisher=Genetech USA, Inc. |access-date=2019-01-20 |archive-date=2018-05-26 |archive-url=https://web.archive.org/web/20180526034324/https://www.gene.com/download/pdf/klonopin_prescribing.pdf |url-status= }}</ref>
|-
|[[도네페질]]||3일(70시간)<ref name="Asiri Mostafa 2010 pp. 117–150">{{서적 인용| last1=Asiri | first1=Yousif A. | last2=Mostafa | first2=Gamal A.E. | title=Profiles of Drug Substances, Excipients and Related Methodology | volume=35 | chapter=Donepezil | publisher=Elsevier | year=2010 | isbn=978-0-12-380884-4 | issn=1871-5125 | doi=10.1016/s1871-5125(10)35003-5 | pmid=22469221 | pages=117–150 | quote=Plasma donepezil concentrations decline with a half-life of approximately 70 h. Sex, race, and smoking history have no clinically significant influence on plasma concentrations of donepezil [46–51].}}</ref>
|-
|[[플루옥세틴]]||4 ~ 6일(지속 투여시)<ref name="fluoxetine">Fluoxetine {{Drugs.com|monograph|fluoxetine}}. Accessed 15 April 2021.</ref>
활성 지용성 대사물질([[노르플루옥세틴]]): 4 ~ 16일<ref name="fluoxetine" />
|-
|[[아미오다론]]
|14 ~ 107일<ref>{{서적 인용|title=Austria-Codex| veditors = Haberfeld H |at=Sedacoron 200 mg-Tabletten|publisher=Österreichischer Apothekerverlag|location=Vienna|year=2020|language=German}}</ref>
|-
|[[반데타닙]]||19일<ref>{{웹 인용|title=Caprelsa (vandetanib) Tablets, for Oral Use. Full Prescribing Information |url=http://www.caprelsa.com/files/caprelsa-pi.pdf |publisher=Sanofi Genzyme, Cambridge, MA, Dec 2016. |access-date=24 February 2020}}</ref>
|-
|[[두타스테리드]]||21 ~ 35일(지속 투여시)<ref>{{서적 인용|title=Austria-Codex| veditors = Haberfeld H |at=Avodart 0,5 mg Weichkapseln|publisher=Österreichischer Apothekerverlag|location=Vienna|year=2020|language=German}}</ref>
|-
|[[베다퀼린]]||165일<ref>{{웹 인용|title=Sirturo (bedaquiline) Tablets. Full Prescribing Information |url=https://www.accessdata.fda.gov/drugsatfda_docs/label/2012/204384s000lbl.pdf |publisher=Janssen Products, Dec 2012. |access-date=24 February 2020}}</ref>
|}

== 같이 보기 ==
* [[반감기]]
* [[유효 반감기]]

== 각주 ==
{{각주}}

{{약리학}}

[[분류:약물동태학]]