Riociguat 1 mg · Tablets

Riociguat is a stimulator of soluble guanylate cyclase (sGC), an enzyme in the cardiopulmonary system and the receptor for nitric oxide (NO).

When NO binds to sGC, the enzyme catalyzes synthesis of the signaling molecule cyclic guanosine monophosphate (cGMP). Intracellular cGMP plays an important role in regulating processes that influence vascular tone, proliferation, fibrosis and inflammation.

Pulmonary hypertension is associated with endothelial dysfunction, impaired synthesis of nitric oxide and insufficient stimulation of the NO-sGC-cGMP pathway.

Riociguat has a dual mode of action. It sensitizes sGC to endogenous NO by stabilizing the NO-sGC binding. Riociguat also directly stimulates sGC via a different binding site, independently of NO.

Riociguat stimulates the NO-sGC-cGMP pathway and leads to increased generation of cGMP with subsequent vasodilation.

The active metabolite (M1) of riociguat is 1/3 to 1/10 as potent as riociguat.

Riociguat pharmacokinetics are dose proportional from 0.5 to 2.5 mg. Inter-individual variability of riociguat exposure (AUC) across all doses is approximately 60%, and within-subject variability is approximately 30%.

The absolute bioavailability of riociguat is about 94%. Peak plasma riociguat concentrations were observed within 1.5 hours after tablet intake. Food does not affect the bioavailability of riociguat.

Bioavailability (AUC and Cmax) of riociguat administered orally as a crushed tablet suspended in applesauce or in water is similar to that of a whole tablet.

The volume of distribution at steady state is approximately 30 L. Plasma protein binding in humans is approximately 95%, with serum albumin and α1–acidic glycoprotein being the main binding components.

Riociguat is mainly cleared through metabolism by CYP1A1, CYP3A4, CYP3A5 and CYP2J2. Formation of the major active metabolite, M1, is catalyzed by CYP1A1, which is inducible by polycyclic aromatic hydrocarbons such as those present in cigarette smoke. M1 is further metabolized to the inactive N-glucuronide. Plasma concentrations of M1 in patients with PAH are about half those for riociguat.

Following oral administration of radiolabeled riociguat in healthy individuals, about 40 and 53% of the total radioactivity was recovered in urine and feces, respectively. There appears to be considerable variability in the proportion of metabolites and unchanged riociguat excreted, but metabolites were the major components of the dose excreted in most individuals.

Average systemic clearance of riociguat was about 1.8 L/h in patients with PAH and about 3.4 L/h in healthy subjects. The terminal elimination half-life is about 12 hours in patients and 7 hours in healthy subjects.

Specific Populations: The effect of intrinsic factors on riociguat and M1 are shown below in Figure 1. There are no clinically relevant effects of age, sex, weight, or race/ethnicity on the pharmacokinetics of riociguat or M1. No dose adjustment is warranted.

Drug interactions: The effect of extrinsic factors on riociguat and M1 were studied in healthy subjects and are shown in Figure 2.

*HIV protease inhibitors are strong CYP3A inhibitors and may increase riociguat plasma concentrations to levels similar to those seen with ketoconazole. ** AUC only, estimated using population pharmacokinetics methods *** AUC only for metabolite, estimated using population pharmacokinetics methods. **** Monitor for signs and symptoms of hypotension on initiation and on treatment with strong CYP and P-gp/BCRP inhibitors [see Dosage and Administration (2.4, 2.5), Warnings and Precautions (5.2) and Drug Interactions (7.2)].

Strong CYP3A inducers: Data are not available to inform dosing of riociguat when strong CYP3A inducers are co-administered [see Drug Interactions (7.2)].

Effects of Riociguat on other Drugs: Riociguat did not affect the pharmacokinetics of midazolam, warfarin, or sildenafil [see Contraindications (4.3) and Clinical Pharmacology (12.2)].

Riociguat (2.5 mg three times per day) did not affect the systemic exposure of combined oral contraceptives containing levonorgestrel and ethinyl estradiol when concomitantly administered to healthy female subjects.