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Pfizer's UK Viagra patent set to expire this month

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Sign up for a free trial of News Direct's animated news graphics at http://newsdirect.nma.com.tw/Reuters.aspx For story suggestions, please contact tips@nma.com.tw Pfizer, maker of blockbuster erectile dysfunction drug Viagra, is expected to face new competitors in the UK when its patent on the drug's process expires later this month. This animation explains the malfunctioning chemical process which Viagra's active ingredient treats. During sexual arousal, the brain signals nerves fibers in arteries. These fibers release nitric oxide which triggers a chemical reaction. Cyclic guanosine monophosphate (cGMP) is then released causing the arteries' walls to relax, increasing blood flow and producing an erection." Meanwhile, the enzyme phosphodiesterase-5, (PDE5) is counteracting the cGMP. As long arousal continues, the heightened blood flow and erection is maintained. In cases of erectile disfunction, insufficient cGMP is produced and is overwhelmed by PDE5. Viagra contains a PDE inhibitor which bonds with the enzyme and stops it from counteracting the cGMP. This allows enough of the chemical to accumulate and relax the artery walls, producing an erection.
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