Many medical disorders could have reasonably predictable effects on the pharmacokinetics of standard psychiatric drugs, but the transition from theoretical data to practical application is often not exact. In the case of kidney failure and lithium therapy, the facts are clear. If renal clearance is decreased, lithium excretion will be decreased in a reasonably proportionate manner. In patients with substantially elevated serum creatinine and blood urea nitrogen who are not in acute renal failure, very small doses of lithium (e.g., 150 mg/day) can be cautiously begun and titrated in the same way as in a healthy patient, but more cautiously and with smaller increments. In this situation, lithium citrate given in milliliter doses could give extra flexibility. Some patients on renal dialysis may be stabilized on lithium, with a single 300-mg dose after each episode of dialysis. This dose may maintain an adequate blood level until the next dialysis removes the lithium ions. Likewise, older patients experience a 30%–40% decrease in glomerular filtration and therefore require lower starting and maximum doses than younger patients.