The invention provides a compound for use in treating or preventing a
disease or condition selected from
cystic fibrosis, chronic obstructive
pulmonary disease (
COPD),
asthma, mild
pulmonary disease,
bronchitis,
bronchiectasis, idiopathic
bronchiectasis, allergic bronchopulmonary
aspergillosis,
sinusitis, rhinosinusitis, CFTR-related
metabolic syndrome (CRMS),
pancreatitis, idiopathic chronic
pancreatitis and Sjörgren'
s syndrome, or for use in preventing
male infertility caused by congenital absence of the
vas deferens, in a patient by modulating CFTR activity, which compound is 9,10-dimethoxy-2-(2,4,6-trimethylphenylimino)-3-(N-carbamoyl-2-aminoethyl)-3,4,6,7-tetrahydro-2H-pyrimido[6,1-a]isoquinolin-4-one or a pharmaceutically acceptable acid addition salt thereof. The invention also provides a composition comprising (i) 9,10-dimethoxy-2-(2,4,6-trimethylphenylimino)-3-(N-carbamoyl-2-aminoethyl)-3,4,6,7-tetrahydro-2H-pyrimido[6,1-a]isoquinolin-4-one or a pharmaceutically acceptable acid addition salt thereof and (ii) a
leukotriene receptor antagonist. The invention also provides a composition comprising (i) 9,10-dimethoxy-2-(2,4,6-trimethylphenylimino)-3-(N-carbamoyl-2-aminoethyl)-3,4,6,7-tetrahydro-2H-pyrimido[6,1-a]isoquinolin-4-one or a pharmaceutically acceptable acid addition salt thereof and (ii) a CFTR
potentiator or a CFTR corrector.