BACKGROUND Anal fissure is perpetuated by high sphincter pressures and secondary local ischaemia. Pharmacological approaches include topical nitrates and botulinum toxin (BT) which act to reduce anal pressure. BT lowers anal pressure by preventing acetylcholine release from nerve terminals while topical nitrates act by donating nitric oxide (NO). The aims of the present study were to compare the therapeutic effect and lowering action on internal anal sphincter pressure of BT injection and local application of isosorbide dinitrate (ID) compared with BT given alone, in patients with chronic anal fissure (CAF) refractory to treatment with ID.

FINDINGS At six weeks the fissure healing rate was significantly higher in group A patients (10/15 (66%)) compared with group B (3/15 (20%)) (p=0.025). At eight and 12 weeks, no significant differences were seen: 11/15 (73%)v 11/15 (73%) and 9/15 (60%)v 10/15 (66%), group Av group B, respectively. Maximum anal resting pressure (MARP) was significantly lower two weeks after BT injection than baseline MARP (90 (4) v 110 (5) mm Hg; p<0.001). A significantly greater reduction in MARP following local application of ID was achieved after BT injection compared with that achieved before BT injection (p=0.037)

INTERPRETATION (1) Combined BT injection and local application of ID in patients with CAF who failed previous treatment with ID was more effective than BT alone. This treatment modality appears to be safe and promising. (2) ID application induced a greater reduction in MARP following BT injection compared with ID application before BT injection. The improved potency of ID on MARP after BT injection suggests a primary cholinergic tonus dominance in some patients and not, as previously claimed, anal sphincter insensitivity to nitrates.