Carbidopa + Levodopa

What it treats and how it works

Levodopa with carbidopa is taken for the symptoms of Parkinson's disease — a brain condition that brings on shaking at rest, muscle stiffness and slowness of movement — and for Parkinson's-like symptoms that follow encephalitis (swelling of the brain) or nervous system damage from carbon monoxide or manganese poisoning. Levodopa is converted in the brain into dopamine, the messenger that helps movements run smoothly, and replacing it eases the tremor, stiffness and slowness. It controls symptoms rather than curing the condition, and it can be several months before the full benefit is felt.

Carbidopa's job in the tablet

Levodopa taken alone is mostly broken down in the gut and bloodstream, so little of it reaches the brain. Carbidopa holds back the enzyme doing that work, which leaves more levodopa for the brain. The upshot is that a smaller levodopa dose does the job, with less nausea and vomiting than levodopa alone, and that is why the two come as one tablet.

Fitting doses into the day

Most people settle into three or four doses spread across the day and keep to roughly the same times each day, so the effect stays even. A tablet can be swallowed with a meal or between meals. A very large, high-fat, high-calorie meal can slow the medicine down, and some people find lighter food easier around dose times. Tablets go down whole. Iron supplements can reduce how much levodopa is absorbed. At the start, doses are usually raised in steps over the first days and weeks rather than begun at the full amount.

What the first weeks can bring

Nausea, vomiting, loss of appetite, dizziness and trouble sleeping are the effects people notice most often at first, and many of them ease as the body adjusts. Dizziness on standing up is common too — low blood pressure is behind it. Urine and sweat may darken; that is harmless. Involuntary jerking or writhing movements (dyskinesia) can develop with long-term use, as can confusion, hallucinations, unusual urges and mood changes. Stopping the tablets abruptly can bring fever, rigid muscles, unusual movements and confusion, so the dose is reduced in steps rather than stopped all at once.

Strengths and the branded tablets

Every strength is written as carbidopa/levodopa: 10/100mg, 25/100mg, 25/250mg and 50/200mg, in packs of 30 to 360 tablets. The first number is the carbidopa, the second the levodopa. The same two ingredients also come as Sinemet, a brand-name tablet in 10/100mg, 25/100mg and 25/250mg. Keep the tablets in their pack somewhere cool and dry.