Ayurveda is a 5,000-year-old system of Hindu traditional medicine native to India. One of the concepts often being mentioned in Ayurveda is Yogvahi (synergism), which is a technique to increase bioavailability, tissue distribution and efficiency of medications.

A natural agent that is capable of enhancing drug bioavailabity upon its co-administration with the active pharmaceutical ingredient (API) is called bioenhancer or biopotentiator.

An example of this breakthrough is a fixed combination (Risorine) of rifampicin, isosoniazid and piperine, which contains only 40 percent of the regular dose rifampicin with the same effect due to increased bioavailability. This decreased effective dose in turn could prevent the drug resistance occurring with regular dose of the drug.

This concept is somewhat new to modern medicine. Many studies have shown drug bioavailability improvement when different bioenhancer herbs were co-administered. This has led to some promising approaches, such as advances in prodrugs, micronization, delayed-release drugs, Sustained-release capsules, absorption enhancers and permeability enhancer dosage forms (emulsions, liposomes).

Furthermore, there has been a great amount of interest in the area of improving oral drug delivery system by co-administration of therapeutic agents and natural bioenhancer compounds (piperine, Quercetin, naringin, genistein, lysergos, niazeridine, capmul, glycyrrhizin, callistemon rigidus, carum carvi (cuminum cyminum or jeera), nitrile glycoside and cow urine distillate (U.S. patented).

One highly studied herbal bioenhancer is piperine, which has up to 98 percent purity if obtained from botanical sources. It has been reported to be able to increase the bioavailability of antitubercular medications (200 mg rifampicin, 300 mg isoniazid and 10 mg piperine), antimicrobial agents (pefloxacin and trikatu; ampicillin and piperine; norfloxacin and piperine), analgesics (5 mg/kg diclofenac sodium and piperine; oentazocine and piperine), and several other drugs.

In the examples provided, piperine and trikatu have been used as herbal bioenhancers, which led to increased strength and potency of the dosage form along with reduced dose-dependent side effects. Piperine was found to be nontoxic as long as it is administered in doses less than 100 mg/kg.

Another group of natural bioenhancers are bioflavonoids, including quercetin, genistin and naringin. Quercetin is found in citrus fruits with a wide range of beneficial biological effects such as antiviral, antioxidant, radical scavenging, anti-inflammatory, antitumor and antiatherosclerotic effects.

The combination of quercetin (5-15 mg/kg) with verapamil (10 mg/kg), diltiazem, paclitaxel, digoxin, doxorubicin and tamoxifen has been reported to effectively increase the bioavailability of these drugs. Likewise, a co-administration of genistein (10 mg/kg), another flavonoid, with paclitaxel (30 mg/kg) was able to show the same increased bioavailabity of the drug. Similarly, co-administration of naringin (3-10 mg/kg), found in grapefruit, with paclitaxel (3 mg/kg) effectively increased the drug's bioavailability.

The specific mechanism of action of these natural bioenhancers varies from efflux transporter inhibition, DNA receptor binding and signal transduction modulation. On the other hand, there may be a few nonspecific mechanisms, such as increased gastrointestinal tract blood supply, decreased hydrochloric acid secretion, drug breakdown prevention and metabolic enzyme inhibition.

Considering that the origin of 75 percent of the antimicrobials and 60 percent of anticancer drugs approved for clinical use could be traced back to natural ingredients, this approach is nothing new. There is a need for more multicenter trials with a combination of new drugs and natural enhancers in order to take advantage of higher potency with a lower-dosage-form toxicity.