Introduction

Black pepper is one of the oldest and best-known spices in the world. Belonged to Piperaceae family, which is cultivated in damp nutrient rich soil of South India, it is also found in Indonesia, Malaysia, and Brazil. In India it is called “kali mirchi”, which is a common household spice.

Its chief constituents are crystalline alkaloid piperine (5 -8.25 %), volatile oils (1-2.3 %) and a resin called Chavicin.₁ Black pepper was found to enhance intestinal absorption of methionine and calcium ions.₂ Piperine, the best-known compound of pepper was reported to inhibit fatty acid oxidation in rat liver microsomes.₃ It is also proved that it increases the bioavailability of theophylline, propanolol and nutrients.₄

The present study was planned to investigate whether Piper Nigrum extract has any analgesic activity and if so how does it interact with diclofenac sodium and pentazocine?

Materials And Methods

The study was carried out on albino mice (20-30 g), maintained under standard laboratory conditions of food and water before start of the experiment. All experiments were carried out between 0900 and 1700 hr according to the guidelines for the care of laboratory animals.₅ Animals were also kept under observation for 7 days, after the completion of experiment to observe acute or sub acute toxicity. The Piper nigrum extract was from Amsar (P) LTD, Indore, India containing 95 % piperine.

Drugs

Study design

Determination of analgesic activity

Statistical analysis

Results

Analgesic activity of individual drugs

(a) Piper nigrum extract

Piper nigrum extract at a dose of 10 mg/kg did not showed any significant effect on tail flick latency also failed to produce any decrease in the number of writhes (P>0.05). [Table 1 & 2]

(b) Diclofenac sodium

Diclofenac sodium at a dose of 5 mg/kg produced significant decrease in number of writhes (P<0.05).

Figure 1

Table 1: Effect of extract (PNE) in acetic acid induced writhings in mice

(c) Pentazocine

In tail flick test, with a dose of 5 mg/kg of pentazocine, significant antinociceptive effect was observed 0.5 hr after the treatment, reaching peak at 2 h and the effect persisted for the entire test period (P<0.05).

Figure 2

Table 2: Effect of (PNE) on tail flick latency in mice

Analgesic activity of Drug combinations

Discussion

Writhing and tail flick methods are the most common test for evaluating the analgesic efficacy of drugs/compound in rodents.

The abdominal constriction response induced by glacial acetic acid is a sensitive procedure to establish peripherally acting analgesics. This response is thought to involve local peritoneal receptors. The number of writhing observed during a 20 min period in control group was 51 ± 0.71 which correspond with the finding of other workers. Piper nigrum extract per se did not show any significant reduction in number of writhes at a dose of 10mg/kg, but when it was combined with diclofenac it significantly reduced the number of writhes greater than that was observed with diclofenac alone group (P< 0.001). We also observed that animals in combination group showed delayed onset of writhes (after 8 -9 min) as compared to other groups in which onset of writhes was within 5 min.

Tail flick method which is used for evaluating centrally acting analgesic effects of drugs showed no increase in latency when Piper nigrum extract alone was administrated. While in combination with pentazocine increased the pain threshold significantly (P <0.01) when compared to pentazocine alone group.

A previous study done with nimesulide in albino mice shows a better therapeutic index and increased effect of nimesulide when co administered with Piperine.₁₀

It is also claimed that piperine has some anti inflammatory activity ₁₁ and anti convulsant activity ₁₂.

Piperine has been reported to enhance the bioavailability of drugs like phenytoin, propanalol, rifampicin in humans.₁₃, ₁₄ This occurs as a result of a nonspecific and noncompetitive inhibitor of the metabolic enzymes.

The result of the present study showed that Piper nigrum extract in dose of 10 mg/kg when combined with diclofenac sodium and pentazocine significantly improves analgesic activity of both the drugs.

In our experiment piperine is enhancing the activity of diclofenac and pentazocine the probable mechanisms of this enhancement may be:

Inhibition of metabolism: Piperine may inhibit different cytochrome P450 isoforms, UDP-glucuronyltransferase, hepatic arylhydrocarbon hydroxylase and other enzymes involved in drug and xenobiotic metabolisms. Piperine has also been found to inhibit CYP3A4 an enzyme important for the metabolism and transport of xenobiotics.₁₅

Improvement in absorption: Piperine improving the absorption of drugs, perhaps by increasing GI blood flow ₁₆ or by increasing permeability of intestinal cells by stimulating gamma-glutamyl transpeptidase activity and increased amino acid uptake.₁₇ The absorption may also be enhanced due to its emulsifying action in the gut.₁₈

Inhibition of efflux: Piperine also inhibits the efflux mechanism perhaps by inhibiting p- glycoprotein, the ‘pump' protein that removes substances from cells. This efflux inhibition promotes the stay of drug within the target cells for a longer period.₁₉

Interference with solubilizer attachment: Some solubilizers such as glucuronic acid linked to the drug to enhance drug elimination. Piperine may inhibit this attachment as it has been shown to reduce the endogeneous UDP- glucuronic acid content of the cells.₂₀

Further studies are needed to reveal the exact mechanism of action responsible for the enhanced activity of diclofenac sodium and pentazocine. However the study adds to our concept that piperine can enhance the activity of diclofenac and pentazocine. So the addition of piperine may reduce the required dose of these drugs that may help in reduction of their toxicity. Hence we recommend further studies to acknowledge their facts.

Acknowledgements