Prevention of peripheral side‐effects of transdermal hyoscine by adjunctive therapy with low dosage of pyridostigmine.

1. The value of low dosage of pyridostigmine (30 mg three times daily) in preventing peripheral anti‐muscarinic side effects of a transdermal controlled‐release formulation of hyoscine, was tested in a double‐ blind placebo‐controlled study, involving 47 healthy subjects. 2. Salivary excretion was repeatedly measured during 48 h of combined therapy of two transdermal hyoscine patches with pyridostigmine and 14 h after its cessation. Blood acetylcholinesterase activity was also measured, serving as an index of pyridostigmine bioavailability. 3. The adjunctive therapy with pyridostigmine was highly effective in preventing the substantial impairment in salivary flow caused by the transdermal formulation. An associated 23% inhibition of blood acetylcholinesterase activity was observed. 4. Small doses of pyridostigmine may therefore have a role in increasing the tolerability of transdermal hyoscine therapy. In some patients this drug combination might also allow some increment of the hyoscine dose. 1992 The British Pharmacological Society