Which drug is most likely causing the "pins and needles" sensation in a patient undergoing treatment for active pulmonary tuberculosis?

Isoniazid is known to cause peripheral neuropathy, which can present as a "pins and needles" sensation often referred to as paresthesia. This side effect occurs due to the drug's interference with vitamin B6 metabolism, which is crucial for the synthesis of neurotransmitters and the maintenance of healthy nerve function. Patients receiving isoniazid may require additional supplementation of vitamin B6 (pyridoxine) to mitigate this side effect and protect against neuropathy.

The other medications listed in the treatment of pulmonary tuberculosis have different side effect profiles. Rifampin can cause hepatotoxicity and orange discoloration of bodily fluids, while pyrazinamide can lead to joint pains and liver enzyme elevation. Ethambutol is primarily associated with optic neuritis, leading to visual disturbances rather than peripheral neurological symptoms. Therefore, among the options, isoniazid is the most likely to cause the "pins and needles" sensation experienced by the patient.