Patients are given GCV intravenously for 14 days. Then the patient receives the same dose, but only once a day, for as long as therapy is tolerated. If the retinitis worsens during the maintenance phase, the patient may again be given GCV for 14 days. Long-term treatment with GCV usually requires the surgical placement of a catheter in a large central vein in the chest or groin that is left in place indefinitely. If this is required, the procedure will be explained to the patient.