Riociguat is the first of a new class of medicines called Guanylate Cyclase Stimulators. These open up blood vessels in the lungs by a similar mechanism to sildenafil and tadalafil. Riociguat has been developed to have theoretical advantages over the PDE5 inhibitors. Clinical trials will help to tell us whether these benefits are borne out in clinical practice.
Riociguat is a tablet which is taken three times a day, ideally with or after food. The tablets should be swallowed whole, but can be chewed or crushed if swallowing is difficult. In some patients riociguat causes a drop in blood pressure. For this reason, everyone takes a “test dose” at the hospital. Having started on this low strength tablet, the dose is increased slowly over a few weeks until the maximum tolerated dose is reached. Whilst this “up-titration” can be done at home, there is regular contact between patients and their PH centre to ensure this process is carried out safely. Patients are encouraged to increase to the dose where any side effects or low blood pressure are experienced, then be reviewed. Riociguat tablets come in a variety of strengths so patients can easily up-titrate their dose, until the appropriate strength can be prescribed as one tablet three times a day.
Do not take riociguat if you:
• Are already taking PDE5 inhibitors (such as sildenafil, tadalafil), nitrates or nitric oxide donors (such as amyl nitrite) in any form including recreational drugs called ‘poppers’.
• Have severe hepatic impairment (Child Pugh C).
• Have had an allergic reaction to riociguat in the past.
• Are pregnant.
• Have a systolic blood pressure less than 95 mm Hg at treatment initiation (this will be checked by the PH centre during the test dose).
• Have pulmonary hypertension associated with idiopathic interstitial pneumonias (a very rare lung condition).
Riociguat is usually well tolerated and the slow up-titration of the dose allows for careful management of side effects. The most frequent complaint from patients is around dyspepsia, and other GI side effects. However the other commonly reported adverse reactions, occurring in 10% of patients on Riociguat are headache, dizziness and peripheral oedema.
Riociguat is the first treatment to be licensed for both PAH and Chronic Thromboembolic Pulmonary Hypertension (CTEPH). If you forget to take a dose of riociguat, simply miss that one and wait until the next dose is due. Never take a double dose to make up for the missed one.