This patient has evidence of cerebellar dysfunction, most likely due to cerebellar hemorrhage. Many drugs (including ciprofloxacin) interact with warfarin, excessively prolong anticoagulation, and may result in spontaneous hemorrhage. Cerebellar lesions are typically associated with ataxia and dizziness. This patient's bleeding can be localized to the right cerebellar hemisphere since a focal lesion in one lobe of the cerebellum (e.g., a cerebellar tumor, hemorrhage or infarct) causes dyscoordination on the same side of the body (ipsilateral) as the lesion. Infarcts in the basal ganglia would cause extrapyramidal signs with rigidity and uncontrolled movements in addition to discoordination. Midline cerebellar lesions (most commonly alcoholic cerebellar degeneration) cause midline signs (especially gait ataxia) out of proportion to the findings in the extremities. Posterior column disease would cause sensory abnormalities (especially, loss of proprioception and vibratory sensation) rather than problems with coordination. Acute alcohol ingestion and narcotic overdose can cause dizziness and ataxia, often with nystagmus, but would not be expected to cause unilateral dysmetria.