Creatinine blood levels reflect how well the kidneys are filtering waste products. In general, normal serum creatinine levels are less than 1.3 milligrams/deciliter for men and less than 1.1 milligrams/deciliter for women. However, a very muscular person or a person who is dehydrated may have a higher value, even though the kidneys are perfectly normal.

Many drugs can raise the creatinine level, and the reasons for the rise vary. Some drugs may:

• Be toxic to the kidney and cause damage that may or may not be reversible, such as the aminoglycoside antibiotics (gentamicin, amikacin, tobramycin), certain chemotherapy agents (cis-platinum, methotrexate) and the antifungal drug amphotericin.
• Cause a temporary decrease in blood flow to the kidney, such as diuretics.
• Alter the pressures within the kidney's small arteries, which can diminish the filtering function, as with the angiotensin converting enzyme inhibitors (ACE inhibitors, including captopril, enalapril, lisinopril, and others), and the angiotensin receptor blockers (or ARBs, including irbesartan, valsartan and others) that are used for high blood pressure and heart failure.
• Temporarily block the excretion of creatinine into the urine without really causing any kidney malfunction, such as the commonly prescribed antibiotic trimethoprim sulfamethoxazole (Bactrim, Septra).

These are just a few examples of the many drugs that can alter the creatinine level.

When a patient develops a new rise in serum creatinine level, all medications, including supplements and over-the-counter products, should be carefully reviewed. One or more of the products may be contributing to the rise. Many drugs that rarely cause kidney problems can be very damaging when used in combination with other drugs or in people with chronic medical conditions.