Posted by: JJ | 2004/11/01

Combivir dosing

After an unfortunate possible HIV exposure I was prescribed Combivir twice daily to take for 28 days. I started this post exposure prophylaxis within 18 hours, and took the first dose at 6pm. As I was instructed to take one tablet twice daily, I have done this and not missed any doses, but took the second dose at about 9am the next day. I realised this is more than 12 hours (15 hours). Both the sticker on the medicine as well as the insert in the drug package say twice daily, rather than every 12 hours, but not I am hearing conflicting information stating these drugs need to be taken every 12 hours with regular intervals. Have I now jeapardised the use of these drugs by waiting so long between the first and second dose? I believe the 3TC component of the drug has a 15 hour or so intracellular half life, but apparently the AZT only has a 3 hour half life, meaning that from about 10 hours or so the AZT is nearly completely dimished. Why dont they specifically stipulate the need to take the drug every 12hours. This could be life threatening.


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Our expert says:
Expert ImagePharmacist

Zidovudine and lamivudine (Combivir) are antiretroviral medications that slow down the replication of the human immunodeficiency virus (HIV) and may therefore slow the progression of HIV disease. They do not cure HIV nor do they prevent HIV transmission. According to the manufacturer if you miss a dose of Combivir, or in your case, take it later than recommended, take it as soon as possible. However, if it is time for your next dose, do not double the dose, just carry on with your regular schedule. It is important to take Combivir on schedule (thus 12 hourly in future), to assure constant, proper blood levels of the drug.

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