['Flap necrosis is generally regarded as the result of vasospasm, thrombosis, and infection.', 'To improve skin flap survival and lower the risk of side effects due to systemic drug delivery, we formulated and evaluated compound gels for transdermal application. The transdermal delivery of 1% azithromycin (AZM), 0.5% amlodipine besylate (AB), and 300 IU/g low molecular weight heparin (LMWH) in compound gels, singly or in combinations, was measured across rat skin in vitro. The effects of AB and LMWH on flap blood circulation was investigated using fluorescein angiography, by transdermally applying the gel onto the surface of an in vivo ischaemic flap rat model; concentrations of the drugs were detected in both blood plasma and flap tissue at assigned timepoints. Finally, infected ischaemic flaps were treated to evaluate their anti-inflammatory effects and sizes of flap survival area.', 'Each drug efficiently penetrated the in vitro skin in a time-dependent manner. In the in vivo ischaemic flaps, AB or LMWH increased the blood supply. All gel formulations that included AZM were associated with less flap inflammation. The surviving areas after treatment with AZM+LMWH or AZM+AB were significantly larger than that treated with the AZM-only gel, and the largest surviving area was that treated with AZM+AB+LMWH. Gels containing no AZM could not decrease flap inflammation or increase flap survival.'] Does transdermal application of azithromycin-amlodipine-heparin gel enhance survival of infected random ischaemic flap?