An 82-year-old woman has fallen twice since her medicines were changed. She is slower when walking and has recently complained of constipation, blurred vision and a dry mouth; her daughter also reports evening confusion. Her medicines are amlodipine, bisoprolol, oxybutynin, paracetamol and tamsulosin. Blood pressure is 126/70 mmHg sitting and 118/68 mmHg standing. Which one of the following medicines should be ceased first?