Approximately 80mg of Blistex Relief Cream is applied to the lips at any one time. Blistex Relief Cream is a topical treatment with locally acting agents.
Any trace quantities of ammonia entering the blood system via Blistex Relief Cream would be so small compared to normal background concentrations of ammonia as to be inconsequential.
Ammonia in the body represents that which is liberated from the deamination of amino acids and the deamination of amides. Portal venous blood contains a high concentration of ammonia. Normally about 20% of the urea produced in the body diffuses into the gut, where it is converted by bacteria to ammonia and carbon dioxide. Intestinal bacteria also produce ammonia from dietary proteins. The ammonia is absorbed and converted back to urea in the liver, by way of the ornithine cycle. Another significant role of ammonia is in the synthesis of glutamine.
Renal excretion – Normal renal venous blood contains a high concentration of ammonia synthesised from glutamine and other amino acids in the kidney. The ammonia that is formed by the kidney is excreted when the urine is acidic, but is largely returned to the systemic circulation if the urine is alkaline. In an acidic urine, NH3 accepts a proton and exists almost entirely as NH4+. Under normal states of metabolism about 70mEq of non-volatile acid is generated per day: about one half of this is excreted in the urine in conjunction with NH4+, and the remainder is excreted as titratable acid. Renal production of ammonia is stimulated by acidosis: ammonia buffers urinary acid and allows further secretion of protons into the tabular fluid. Potassium depletion also results in a primary increase in the alkalinization of the urine (Tannen, 1977). This may increase the amount of ammonia that is returned to the circulation via the renal vein and have a deleterious effect when potassium depletion coexists with hepatic failure.
Normal physiological mechanisms are designed to keep the concentration of ammonia in the blood as low as possible. Thus, ammonia added to the venous circulation by the kidney or gastrointestinal tract is converted to urea by the liver.
Phenol – A paper published by JAMA in 1953 showed that phenol readily penetrates the human skin and that detoxification by conjugation is initiated immediately.
The pharmaceutical form of Blistex Relief Cream is similar to the aromatised liquid petrolatum of Camphor phenique. This being so, we would expect that after local application the amount of phenol in blood attributable to Blistex Relief Cream would be of the order of 0.0003 mg/100ml of blood.
According to the Journal of Clinical Pathology 12:129, 1942 the residual phenol content of blood in normal human beings varies from 0.0 to 0.08 mg/100ml free phenol and 0.0 to 0.08 mg/100ml conjugated phenol.
This suggests that residual phenol in normal humans can be anything up to 250 times greater than that which is likely to come from Blistex Relief Cream.
The results of the 1953 paper indicate that phenol from Blistex Relief Cream is rapidly absorbed through the skin and is rapidly detoxified due to its extremely low concentrations.