Tadalafil and vardenafil


In 2003, two inhibitors of phosphodiesterase 5 (PDE5) — tadalafil (Cialis; Lilly ICOS) and vardenafil hydrochloride (Levitra; Bayer/ GlaxoSmithKline) — were approved by the US FDA for the treatment of erectile dysfunction. Can they challenge the dominance of the first PDE5 inhibitor, sildenafil citrate (Viagra; Pfizer), which rapidly became a blockbuster following its market entry in the late 1990s?

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Figure 1: PDE5 inhibition.
Figure 2: Market for drugs to treat erectile dysfunction in US $ million.


  1. 1

    Lue, T. F. Erectile dysfunction. N. Engl. J. Med. 342, 1802–1813 (2000).

  2. 2

    NIH Consensus Conference. Impotence. NIH Consensus Development Panel on Impotence. JAMA 270, 83–90 (1993).

  3. 3

    Rotella, D. P. Phosphodiesterase 5 inhibitors: current status and potential applications. Nature Rev. Drug Disc. 1, 674–682 (2002).

  4. 4

    Terrett, N. K. et al. Sildenafil (Viagra), a potent and selective inhibitor of type 5 cGMP phosphodiesterase with utility for the treatment of male erectile dysfunction. Bioorg. Med. Chem. Lett. 6, 1819–1824 (1996).

  5. 5

    Daugan, A. et al. The discovery of tadalafil: a novel and highly selective PDE5 inhibitor. 1:5,6,11,11a-tetrahydro-1H-imidazo[1′,5′:1,6]pyrido[3,4-b]indole-1,3(2H)-dione analogues. J. Med. Chem. 46, 4525–4532 (2003).

  6. 6

    Daugan, A. et al. The discovery of tadalafil: a novel and highly selective PDE5 inhibitor. 2: 2,3,6,7,12,12a-hexahydropyrazino[1′,2′:1,6]pyrido[3,4-b]indole-1,4-dione analogues. J. Med. Chem. 46, 4533–4542 (2003).

  7. 7

    Haning, H. et al. Imidazo[5,1-f][1,2,4]triazin-4(3H)-ones, a new class of potent PDE 5 inhibitors. Bioorg. Med. Chem. Lett. 12, 865–868 (2002).

  8. 8

    FDA Drug Approvals List [online], (cited 10 Feb 2004), <http://www.fda.gov/cder/foi/label/2003/021368lbl.pdf> (2003).

  9. 9

    FDA Drug Approvals List [online], (cited 10 Feb 2004), <http://www.fda.gov/cder/foi/label/2003/021400lbl.pdf> (2003).

  10. 10

    Rajfer, J. et al. Nitric oxide as a mediator of relaxation of the corpus cavernosum in response to nonadrenergic, noncholinergic neurotransmission. N. Engl. J. Med. 326, 90–94 (1992).

Download references

Author information

Correspondence to Katherine Neumeyer.

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Neumeyer, K., Kirkpatrick, P. Tadalafil and vardenafil. Nat Rev Drug Discov 3, 295–296 (2004). https://doi.org/10.1038/nrd1362

Download citation

Further reading