Resumo: A thermodynamical formalism is developed for a system of interacting particles under overdamped motion, which is analyzed within the framework of nonextensive statistical mechanics. It amounts to express the interaction energy of the system in terms of a temperature theta, conjugated to a generalized entropy s_q, with q=2. Since theta assumes much higher values than those of typical room temperatures T«theta, the thermal noise can be neglected for this system (T/theta~=0). The introduction of a work term delta W which, together with the heat contribution (delta Q = theta ds_q), allows for the statement of a proper energy conservation law that is analogous to the first law of thermodynamics. These definitions lead to the derivation of an equation of state and to the characterization of s_q-adiabatic and theta-isothermic transformations. On this basis, a Carnot cycle is constructed, whose efficiency is shown to be \eta=1-(theta_2/theta_1), where theta_1 and theta_2 are the effective temperatures of the two isothermic transformations, with theta_1>theta_2. All results presented are consistent with those of standard thermodynamics for T>0, opening the possibility for further physical consequences.