Monoclonal antibodies. Administration of rabies virus–neutralizing monoclonal antibodies (e.g., monoclonal antibody 1112-1) has been shown to clear rabies virus infection from the CNS in a rodent model when administered before the onset of clinical signs, resulting in the survival of experimentally infected rats [23]. This suggests that therapy with ⩾1 monoclonal antibodies may prove to be effective therapeutically in the future. Human monoclonal antibodies or humanized mouse monoclonal antibodies would be preferable to mouse monoclonal antibodies. Evaluation of this strategy would require development of an investigational drug protocol.
Ribavirin. Ribavirin (1-β-D-Ribofuranosyl-1H-1,2,4-triazole-3-carboxamide) is a broad-spectrum antiviral agent with many intrinsic mechanisms that can influence its overall antiviral properties [19]. Ribavirin is a purine analogue and an RNA mutagen that induces mutations by acting as a template for incorporation of cytidine and uridine with equal efficiency [24]. Ribavirin also has immunomodulatory properties that may, in part, account for its antiviral properties in vivo [25]. Ribavirin has in vitro activity against rabies virus infection [26, 27], although efficacy was not demonstrated in a study that used animal models [28]. Ribavirin is typically administered intravenously with both loading and maintenance doses. There is limited information about its penetration across the intact blood-brain barrier, which may be marginal, because rapid uptake into CSF was not observed in rats and rhesus monkeys [29]. However, significant levels of ribavirin were observed in CSF after orally administered ribavirin therapy was given for several weeks to patients with AIDS and AIDS-related complex [30]. Intraventricular administration of ribavirin via an Ommaya reservoir, in addition to therapy by the intravenous route, would be a therapeutic option at the present time. One patient with rabies who was treated with a combination of intrathecal and intravenous ribavirin therapy demonstrated no apparent benefit [16].