Ritonavir

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Ritonavir
Systematic (IUPAC) name
1,3-thiazol-5-ylmethyl N-[(2S,3S,5S)-3-hydroxy-5-[(2S)-3-methyl-2-{[methyl({[2-(propan-2-yl)-1,3-thiazol-4-yl]methyl})carbamoyl]amino}butanamido]-1,6-diphenylhexan-2-yl]carbamate
Clinical data
Trade names Norvir
AHFS/Drugs.com monograph
MedlinePlus a696029
Pregnancy cat. B (U.S.)
Legal status ℞-only (U.S.)
Routes oral
Pharmacokinetic data
Protein binding 98-99%
Half-life 3-5 hours
Excretion mostly fecal
Identifiers
CAS number 155213-67-5 YesY
ATC code J05AE03
PubChem CID 392622
DrugBank DB00503
ChemSpider 347980 YesY
UNII O3J8G9O825 YesY
KEGG D00427 YesY
ChEMBL CHEMBL163 YesY
NIAID ChemDB 028478
Chemical data
Formula C37H48N6O5S2 
Mol. mass 720.946 g/mol
 YesY (what is this?)  (verify)

Ritonavir, with trade name Norvir (Abbott Laboratories), is an antiretroviral drug from the protease inhibitor class used to treat HIV infection and AIDS.

Ritonavir is frequently prescribed with HAART, not for its antiviral action, but as it inhibits the same host enzyme that metabolizes other protease inhibitors. This inhibition leads to higher plasma concentrations of these latter drugs, allowing the clinician to lower their dose and frequency and improving their clinical efficacy.

Contents

History [edit]

Ritonavir is manufactured as Norvir by Abbott Laboratories. Research that led to the drug's development was financed by a $3,500,000 federal grant through the National Institutes of Health (NIH) and over $200,000,000 by Abbott Labs. Most of the $200,000,000 figure cited by Abbott paid for clinical trials—despite NIH offering to pay for them—because Abbott was concerned about "public interest" responses to the high prices they projected Norvir would command.[1] The Food and Drug Administration (FDA) approved ritonavir on March 1, 1996, making it the seventh approved antiretroviral drug in the United States. In 2003, Abbott raised the price of a Norvir course from USD $1.71 per day to $8.57 per day, leading to claims of price gouging by patients' groups and some members of Congress. Consumer group Essential Inventions petitioned the NIH to override the Norvir patent, but the NIH announced on August 4, 2004 that it lacked the legal right to allow generic production of Norvir.[2]

Mechanism of action [edit]

Ritonavir (center) bound to the active site of HIV protease.

Ritonavir was originally developed as an inhibitor of HIV protease. It is one of the most complex inhibitors. It is now rarely used for its own antiviral activity, but remains widely used as a booster of other protease inhibitors. More specifically, ritonavir is used to inhibit a particular liver enzyme that normally metabolizes protease inhibitors, cytochrome P450-3A4 (CYP3A4).[3] The drug's molecular structure inhibits CYP3A4, so a low dose can be used to enhance other protease inhibitors. This discovery, which has drastically reduced the adverse effects and improved the efficacy of PI's and HAART, was first communicated in an article published in the journal AIDS in 1997 by researchers at the University of Liverpool.[4] This effect does come with a price: it also affects the efficacy of numerous other medications, making it difficult to know how to administer them concurrently. In addition it can cause a large number of side-effects on its own.

Drug interactions [edit]

Concomitant therapy of ritonavir with a variety of medications may result in serious and sometimes fatal drug interactions.[5] Ritonavir induces CYP 1A2 and inhibits the major P450 isoforms (3A4 and 2D6).

The list of clinically significant interactions of ritonavir includes but is not limited to following drugs:

Side effects [edit]

The most common side effects of ritonavir therapy are:[6]

One of ritonavir's side effects is hyperglycemia. It appears that ritonavir directly inhibits the GLUT4 insulin-regulated transporter, keeping glucose from entering fat and muscle cells.[citation needed] This can lead to insulin resistance and cause problems for Type Ⅱ diabetics.

Appearance of a second crystal form and temporary withdrawal from the market [edit]

Norvir was originally dispensed as an ordinary capsule, which did not require refrigeration. This was as a crystal of what is now called form I.[7] However, like many drugs, ritonavir exhibits polymorphism, i.e., the same molecule crystallizes into more than one type of crystal. The different crystals, or polymorphs, are made of the same molecules but in different crystalline arrangements. The solubility and hence the bioavailability is very different in the two different arrangements.[8]

During development (it was introduced in 1996), only the polymorph now called form I was found, but in 1998, a lower free energy, more stable polymorph (form II) appeared. This more stable (and so less soluble) crystal form compromised the oral bioavailability of the drug. This caused the removal of the oral capsule formulation from the market.[8]

Even a trace of form II can catalyse the transformation from the more bioavailable form I to form II. Thus form II threatened existing supplies of ritonavir as the lower solubility polymorph caused the therapeutically effective polymorph to convert to form II. Form II, which was not therapeutically effective because of poor solubility and resulting much lower bioavailability, entered production lines and effectively halted production processes.[7]

After this discovery in the late 1990s, Abbott withdrew the original capsules from the market, and recommended patients switch to Norvir suspension while researchers worked to solve the problem. The capsules have been replaced with refrigerated gelcaps, to solve the crystallization problem of the original capsules.

References [edit]

  1. ^ James Love (2004-06-03). "How much has the public invested in ritonavir, and how much has Abbott?". Essential Inventions. Retrieved 2008-05-06. .
  2. ^ Ceci Connolly (2004-08-05). "NIH Declines to Enter AIDS Drug Price Battle". Washington Post. Retrieved 2006-01-16. 
  3. ^ Zeldin RK, Petruschke RA (2004). "Pharmacological and therapeutic properties of ritonavir-boosted protease inhibitor therapy in HIV-infected patients". Journal of Antimicrobial Chemotherapy 53 (1): 4–9. doi:10.1093/jac/dkh029. PMID 14657084. 
  4. ^ Merry, Concepta; Barry, Michael G.; Mulcahy, Fiona; Ryan, Mairin; Heavey, Jane; Tjia, John F.; Gibbons, Sara E.; Breckenridge, Alasdair M.; Back, David J. (1997). "Saquinavir pharmacokinetics alone and in combination with ritonavir in HIV-infected patients". AIDS 11 (4): F29–F33. doi:10.1097/00002030-199704000-00001. PMID 9084785. 
  5. ^ Ritonavir, Merck Manual
  6. ^ Norvir, rxlist.com
  7. ^ a b Bauer J, et al. (2004). "Ritonavir: An Extraordinary Example of Conformational Polymorphism". Pharmaceutical Research 18 (6): 859–866. doi:10.1023/A:1011052932607. PMID 11474792. 
  8. ^ a b S. L. Morisette, S. Soukasene, D. Levinson, M. J. Cima and O. Almarsson (2003). "Elucidation of crystal form diversity of the HIV protease inhibitor ritonavir by high-throughput crystallization". Proc. Natl. Acad. Sci. USA 100 (5): 2180–4. doi:10.1073/pnas.0437744100. PMC 151315. PMID 12604798. 

Further reading [edit]

  • Chemburkar, Sanjay R.; Bauer, John; Deming, Kris; Spiwek, Harry; Patel, Ketan; Morris, John; Henry, Rodger; Spanton, Stephen et al. (2000). "Dealing with the Impact of Ritonavir Polymorphs on the Late Stages of Bulk Drug Process Development". Organic Process Research & Development 4 (5): 413. doi:10.1021/op000023y. 

External links [edit]

Antiviral drugs: antiretroviral drugs used against HIV (primarily J05)
Entry/fusion inhibitors
(Discovery & development)
Reverse-transcriptase
inhibitors (RTIs)
Integrase inhibitors
Maturation inhibitors
Protease Inhibitors (PI)
(Discovery and development)
1st generation
2nd generation
Combined formulations
Experimental agents
Other
Failed agents
°DHHS preferred first-line agent. ◊Formerly or rarely used agent.
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