A doctor asks if it is possible to make bisoprolol in liquid form

There bisoprolol is not available in bulk you will have to assume a spécialité, which contains bisoprololfumarate. I suppose that if you write "the client takes 5 mg per day Bisoprolol", which you mean herewith bisoprololfumarate. All spécialités contain the fumarate.  

You will need to make some tablets fine, best with a small electric coffee grinder. After grinding   The obtained powder is sieved.   which stays behind on the sieve is further ground.   and then you can continue to work with follose composition

Bisoprolol Fumarate 100 mg; Nabenzate 100 mg; Nasaccharinate 150 mg; HPMC 4,000 100 mg; Phosphate buffer pH 4.0   to 100 ml.  

The composition of the phosphate buffer pH 4.0 reads:   61,5 ml 0.1 M citric acid. 1aq     and 38.5 ml 0.2 M NaH2PO 4.2 aq  

0.1 M Citric acid 1aq   contains 21 g/L   and 0.2 M NaH2PO 4.2 aq contains 35.8 G/L